ACT Science : How to find conflicting viewpoints in physics

Study concepts, example questions & explanations for ACT Science

varsity tutors app store varsity tutors android store varsity tutors ibooks store

Example Questions

Example Question #21 : How To Find Conflicting Viewpoints In Physics

In a physics class, students conducted a series of experiments by placing different objects into a beaker of water. They conducted twenty trials for each object. For each trial, they recorded whether or not the object floated.

First, they placed a steel paper clip into the water. They observed that the paper clip usually sank; however, they also saw that occasionally, the paper clip stayed afloat if it was placed very gently on top of the water. Next, they repeated the the same procedure using a cork, a toy boat made of aluminum, and a glass marble. They observed that both the cork and the toy boat always stayed afloat in the water, but that the glass marble always sank.

Below, three students give their explanations for these observations.

 

Student 1:

Objects float when they are less dense than the liquid in which they are immersed. For example, when immiscible liquids of varying densities are mixed together in a container, the most dense liquid will sink to the bottom of the container, while the least dense liquid will rise to the top. This same principle applies to solid objects. Because the cork and the aluminum toy boat always float, cork and the aluminum of the boat must be less dense than water. Because the glass marble always sinks, the glass of the marble must be more dense than water.

Objects that are more dense than water can also float due to surface tension. Surface tension occurs because molecules of a liquid are more attracted to each other more than they are to other objects. Molecules on the surface of water are attracted to the molecules around them and below them. This attraction causes a liquid's surface to behave if it were covered by a thin film, which resists penetration by other objects. Therefore, small objects such as paper clips can sometimes float on water when the upward force of water's surface tension exceeds the force of gravity pulling such objects down. Because the paper clips often sink and only float sometimes, we can conclude that they are indeed more dense than water, and that their floating is due to surface tension.

 

Student 2:

Objects float in two different cases: when they are buoyed by a liquid's surface tension or when their average density is less than that of the liquid in which they are immersed. The average density of cork is less than that of water. This is why the cork floats. In contrast, the density of glass is more than that of water. This is why the glass marble sinks.

However, the densities of aluminum and of steel are greater than that of water. Thus, density cannot be used to explain why the aluminum toy boat and the paper clip float. Both of these objects float because of surface tension. Because the paper clip does not have much mass, the normal upward force created by water's surface tension can be enough to allow it to float. Other objects with greater mass, like the toy boat, employ a particular shape to magnify the force of surface tension. The curved shape of the boat's bottom both stabilizes the boat and increases the amount of the boat's surface area that touches the water, maximizing the force due to surface tension that the boat receives.

 

Student 3:

In this experiment, the paper clip floats because of surface tension; however, the cork, toy boat, and marble float or sink because of their relationship to a buoyant force. All objects immersed in a liquid experience a buoyant force, which pushes them upward. The strength of this force is equal to the weight of the liquid displaced, or pushed aside, by an object. Every object also experiences a downward force due to gravity, which is measured as the object's weight, and which is directly proportional to the object's mass. When the buoyant force acting on an object is greater than the downward force due to gravity, the object floats. However, when the buoyant force is less than the force due to gravity, the object sinks. Both the cork and the aluminum toy boat are able to displace enough water to create a buoyant force that exceeds the force due to gravity, so they float. However, the glass marble does not displace enough water to create a sufficient buoyant force, so it sinks.

Given that Student2's explanation is correct, which of the following objects is most likely to float?

Possible Answers:

An object with a mass of 100 g and a volume of 100 cm3

An object with a mass of 50 g and a volume of 50 cm3

An object with a mass of 50 g and a volume of 100 cm3

An object with a mass of 100 g and a volume of 50 cm3

Correct answer:

An object with a mass of 50 g and a volume of 100 cm3

Explanation:

According to Student 2, objects will definitely float if their average density is less than that of water. So, we have to find out which of the objects described in the answer choices has the least density. The least dense object is the one that contains the least mass (50 g) in the greatest volume (100 cm3).

Example Question #152 : Physics

In a physics class, students conducted a series of experiments by placing different objects into a beaker of water. They conducted twenty trials for each object. For each trial, they recorded whether or not the object floated.

First, they placed a steel paper clip into the water. They observed that the paper clip usually sank; however, they also saw that occasionally, the paper clip stayed afloat if it was placed very gently on top of the water. Next, they repeated the the same procedure using a cork, a toy boat made of aluminum, and a glass marble. They observed that both the cork and the toy boat always stayed afloat in the water, but that the glass marble always sank.

Below, three students give their explanations for these observations.

 

Student 1:

Objects float when they are less dense than the liquid in which they are immersed. For example, when immiscible liquids of varying densities are mixed together in a container, the most dense liquid will sink to the bottom of the container, while the least dense liquid will rise to the top. This same principle applies to solid objects. Because the cork and the aluminum toy boat always float, cork and the aluminum of the boat must be less dense than water. Because the glass marble always sinks, the glass of the marble must be more dense than water.

Objects that are more dense than water can also float due to surface tension. Surface tension occurs because molecules of a liquid are more attracted to each other more than they are to other objects. Molecules on the surface of water are attracted to the molecules around them and below them. This attraction causes a liquid's surface to behave if it were covered by a thin film, which resists penetration by other objects. Therefore, small objects such as paper clips can sometimes float on water when the upward force of water's surface tension exceeds the force of gravity pulling such objects down. Because the paper clips often sink and only float sometimes, we can conclude that they are indeed more dense than water, and that their floating is due to surface tension.

 

Student 2:

Objects float in two different cases: when they are buoyed by a liquid's surface tension or when their average density is less than that of the liquid in which they are immersed. The average density of cork is less than that of water. This is why the cork floats. In contrast, the density of glass is more than that of water. This is why the glass marble sinks.

However, the densities of aluminum and of steel are greater than that of water. Thus, density cannot be used to explain why the aluminum toy boat and the paper clip float. Both of these objects float because of surface tension. Because the paper clip does not have much mass, the normal upward force created by water's surface tension can be enough to allow it to float. Other objects with greater mass, like the toy boat, employ a particular shape to magnify the force of surface tension. The curved shape of the boat's bottom both stabilizes the boat and increases the amount of the boat's surface area that touches the water, maximizing the force due to surface tension that the boat receives.

 

Student 3:

In this experiment, the paper clip floats because of surface tension; however, the cork, toy boat, and marble float or sink because of their relationship to a buoyant force. All objects immersed in a liquid experience a buoyant force, which pushes them upward. The strength of this force is equal to the weight of the liquid displaced, or pushed aside, by an object. Every object also experiences a downward force due to gravity, which is measured as the object's weight, and which is directly proportional to the object's mass. When the buoyant force acting on an object is greater than the downward force due to gravity, the object floats. However, when the buoyant force is less than the force due to gravity, the object sinks. Both the cork and the aluminum toy boat are able to displace enough water to create a buoyant force that exceeds the force due to gravity, so they float. However, the glass marble does not displace enough water to create a sufficient buoyant force, so it sinks.

In an experiment, an apple is attached to a spring scale. The reading on the scale shows how much upward force is exerted by the spring to keep the apple suspended in place. If Student 3's explanation is correct, how will the reading on the scale change when the apple is placed partway in water? The reading on the scale will be __________.

Possible Answers:

less, because a buoyant force decreases the amount of upward force needed to keep the apple in place

the same, because the mass of the apple does not change when it is placed partway in water

more, because a buoyant force increases the amount of upward force needed to keep the apple in place

less, because a force due to surface tension decreases the amount of upward force needed to keep the apple in place

more, because a force due to surface tension increases the amount of upward force needed to keep the apple in place

Correct answer:

less, because a buoyant force decreases the amount of upward force needed to keep the apple in place

Explanation:

This question involves making some inferences. Student 3 says that when objects are in water, they experience an upward buoyant force. So, when the apple is placed partway in water, it experiences an upward buoyant force that it did not experience when it was out of the water. Because of this additional buoyant force from the water, the spring scale needs to exert less force to keep the apple suspended where it is. So, the reading on the scale will be less when the apple is partway in water.

Example Question #1274 : Act Science

In a physics class, students conducted a series of experiments by placing different objects into a beaker of water. They conducted twenty trials for each object. For each trial, they recorded whether or not the object floated.

First, they placed a steel paper clip into the water. They observed that the paper clip usually sank; however, they also saw that occasionally, the paper clip stayed afloat if it was placed very gently on top of the water. Next, they repeated the the same procedure using a cork, a toy boat made of aluminum, and a glass marble. They observed that both the cork and the toy boat always stayed afloat in the water, but that the glass marble always sank.

Below, three students give their explanations for these observations.

 

Student 1:

Objects float when they are less dense than the liquid in which they are immersed. For example, when immiscible liquids of varying densities are mixed together in a container, the most dense liquid will sink to the bottom of the container, while the least dense liquid will rise to the top. This same principle applies to solid objects. Because the cork and the aluminum toy boat always float, cork and the aluminum of the boat must be less dense than water. Because the glass marble always sinks, the glass of the marble must be more dense than water.

Objects that are more dense than water can also float due to surface tension. Surface tension occurs because molecules of a liquid are more attracted to each other more than they are to other objects. Molecules on the surface of water are attracted to the molecules around them and below them. This attraction causes a liquid's surface to behave if it were covered by a thin film, which resists penetration by other objects. Therefore, small objects such as paper clips can sometimes float on water when the upward force of water's surface tension exceeds the force of gravity pulling such objects down. Because the paper clips often sink and only float sometimes, we can conclude that they are indeed more dense than water, and that their floating is due to surface tension.

 

Student 2:

Objects float in two different cases: when they are buoyed by a liquid's surface tension or when their average density is less than that of the liquid in which they are immersed. The average density of cork is less than that of water. This is why the cork floats. In contrast, the density of glass is more than that of water. This is why the glass marble sinks.

However, the densities of aluminum and of steel are greater than that of water. Thus, density cannot be used to explain why the aluminum toy boat and the paper clip float. Both of these objects float because of surface tension. Because the paper clip does not have much mass, the normal upward force created by water's surface tension can be enough to allow it to float. Other objects with greater mass, like the toy boat, employ a particular shape to magnify the force of surface tension. The curved shape of the boat's bottom both stabilizes the boat and increases the amount of the boat's surface area that touches the water, maximizing the force due to surface tension that the boat receives.

 

Student 3:

In this experiment, the paper clip floats because of surface tension; however, the cork, toy boat, and marble float or sink because of their relationship to a buoyant force. All objects immersed in a liquid experience a buoyant force, which pushes them upward. The strength of this force is equal to the weight of the liquid displaced, or pushed aside, by an object. Every object also experiences a downward force due to gravity, which is measured as the object's weight, and which is directly proportional to the object's mass. When the buoyant force acting on an object is greater than the downward force due to gravity, the object floats. However, when the buoyant force is less than the force due to gravity, the object sinks. Both the cork and the aluminum toy boat are able to displace enough water to create a buoyant force that exceeds the force due to gravity, so they float. However, the glass marble does not displace enough water to create a sufficient buoyant force, so it sinks.

Which of the following, if found, provides the strongest evidence against Student 3's explanation?

Possible Answers:

When two toy boats with the same mass and shape are placed in water, the toy boat with a greater volume sinks, while the object with the smaller volume floats.

The buoyant force experienced by objects changes slightly with the temperature of the water they are in.

While a glass marble weighs 30 g, the volume of water displaced by the marble only weighs 20 g.

When a plastic baggie is filled completely with water, sealed, and placed in a container of water, it neither sinks nor floats to the surface, but stays suspended in the water.

Correct answer:

When two toy boats with the same mass and shape are placed in water, the toy boat with a greater volume sinks, while the object with the smaller volume floats.

Explanation:

According to Student 3's explanation, objects that displace more water will experience a greater buoyant force. If two objects have the same mass and shape, bigger object should displace more water, and therefore experience a greater buoyant force and be more likely to float. So, when the mass and shape of two toy boats are the same, we should expect the bigger toy boat (the one with a bigger volume) to be more likely to float; however, if the toy boat with the bigger volume actually sinks, while a toy boat with a smaller volume floats, this would weaken Student 3's argument.

Example Question #162 : Physics

In a physics class, students conducted a series of experiments by placing different objects into a beaker of water. They conducted twenty trials for each object. For each trial, they recorded whether or not the object floated.

First, they placed a steel paper clip into the water. They observed that the paper clip usually sank; however, they also saw that occasionally, the paper clip stayed afloat if it was placed very gently on top of the water. Next, they repeated the the same procedure using a cork, a toy boat made of aluminum, and a glass marble. They observed that both the cork and the toy boat always stayed afloat in the water, but that the glass marble always sank.

Below, three students give their explanations for these observations.

 

Student 1:

Objects float when they are less dense than the liquid in which they are immersed. For example, when immiscible liquids of varying densities are mixed together in a container, the most dense liquid will sink to the bottom of the container, while the least dense liquid will rise to the top. This same principle applies to solid objects. Because the cork and the aluminum toy boat always float, cork and the aluminum of the boat must be less dense than water. Because the glass marble always sinks, the glass of the marble must be more dense than water.

Objects that are more dense than water can also float due to surface tension. Surface tension occurs because molecules of a liquid are more attracted to each other more than they are to other objects. Molecules on the surface of water are attracted to the molecules around them and below them. This attraction causes a liquid's surface to behave if it were covered by a thin film, which resists penetration by other objects. Therefore, small objects such as paper clips can sometimes float on water when the upward force of water's surface tension exceeds the force of gravity pulling such objects down. Because the paper clips often sink and only float sometimes, we can conclude that they are indeed more dense than water, and that their floating is due to surface tension.

 

Student 2:

Objects float in two different cases: when they are buoyed by a liquid's surface tension or when their average density is less than that of the liquid in which they are immersed. The average density of cork is less than that of water. This is why the cork floats. In contrast, the density of glass is more than that of water. This is why the glass marble sinks.

However, the densities of aluminum and of steel are greater than that of water. Thus, density cannot be used to explain why the aluminum toy boat and the paper clip float. Both of these objects float because of surface tension. Because the paper clip does not have much mass, the normal upward force created by water's surface tension can be enough to allow it to float. Other objects with greater mass, like the toy boat, employ a particular shape to magnify the force of surface tension. The curved shape of the boat's bottom both stabilizes the boat and increases the amount of the boat's surface area that touches the water, maximizing the force due to surface tension that the boat receives.

 

Student 3:

In this experiment, the paper clip floats because of surface tension; however, the cork, toy boat, and marble float or sink because of their relationship to a buoyant force. All objects immersed in a liquid experience a buoyant force, which pushes them upward. The strength of this force is equal to the weight of the liquid displaced, or pushed aside, by an object. Every object also experiences a downward force due to gravity, which is measured as the object's weight, and which is directly proportional to the object's mass. When the buoyant force acting on an object is greater than the downward force due to gravity, the object floats. However, when the buoyant force is less than the force due to gravity, the object sinks. Both the cork and the aluminum toy boat are able to displace enough water to create a buoyant force that exceeds the force due to gravity, so they float. However, the glass marble does not displace enough water to create a sufficient buoyant force, so it sinks.

Given that all of the following are true, which of the following, if found, provides the strongest evidence against Student 1's explanation?

Possible Answers:

Fresh water has a density of 1.00 g/cm3, while salt water has a density of 1.03 g/cm3.

Fresh water has a density of 1.00 g/cm3, while aluminum has a density of 2.70 g/cm3.

Fresh water has a density of 1.00 g/cm3, while glass has a density of 2.61 g/cm3.

Fresh water has a density of 1.00 g/cm, while cork has a density of 0.23 g/cm3.

Correct answer:

Fresh water has a density of 1.00 g/cm3, while aluminum has a density of 2.70 g/cm3.

Explanation:

Student 1 states that the cork and aluminum toy boat both float because cork and aluminum are less dense than water; however, if the density of water is 1.00 g/cm3, while the density of aluminum is 2.70 g/cm3, aluminum is actually more dense than water, which contradicts Student 1's explanation.

Example Question #21 : How To Find Conflicting Viewpoints In Physics

In a physics class, students conducted a series of experiments by placing different objects into a beaker of water. They conducted twenty trials for each object. For each trial, they recorded whether or not the object floated.

First, they placed a steel paper clip into the water. They observed that the paper clip usually sank; however, they also saw that occasionally, the paper clip stayed afloat if it was placed very gently on top of the water. Next, they repeated the the same procedure using a cork, a toy boat made of aluminum, and a glass marble. They observed that both the cork and the toy boat always stayed afloat in the water, but that the glass marble always sank.

Below, three students give their explanations for these observations.

 

Student 1:

Objects float when they are less dense than the liquid in which they are immersed. For example, when immiscible liquids of varying densities are mixed together in a container, the most dense liquid will sink to the bottom of the container, while the least dense liquid will rise to the top. This same principle applies to solid objects. Because the cork and the aluminum toy boat always float, cork and the aluminum of the boat must be less dense than water. Because the glass marble always sinks, the glass of the marble must be more dense than water.

Objects that are more dense than water can also float due to surface tension. Surface tension occurs because molecules of a liquid are more attracted to each other more than they are to other objects. Molecules on the surface of water are attracted to the molecules around them and below them. This attraction causes a liquid's surface to behave if it were covered by a thin film, which resists penetration by other objects. Therefore, small objects such as paper clips can sometimes float on water when the upward force of water's surface tension exceeds the force of gravity pulling such objects down. Because the paper clips often sink and only float sometimes, we can conclude that they are indeed more dense than water, and that their floating is due to surface tension.

 

Student 2:

Objects float in two different cases: when they are buoyed by a liquid's surface tension or when their average density is less than that of the liquid in which they are immersed. The average density of cork is less than that of water. This is why the cork floats. In contrast, the density of glass is more than that of water. This is why the glass marble sinks.

However, the densities of aluminum and of steel are greater than that of water. Thus, density cannot be used to explain why the aluminum toy boat and the paper clip float. Both of these objects float because of surface tension. Because the paper clip does not have much mass, the normal upward force created by water's surface tension can be enough to allow it to float. Other objects with greater mass, like the toy boat, employ a particular shape to magnify the force of surface tension. The curved shape of the boat's bottom both stabilizes the boat and increases the amount of the boat's surface area that touches the water, maximizing the force due to surface tension that the boat receives.

 

Student 3:

In this experiment, the paper clip floats because of surface tension; however, the cork, toy boat, and marble float or sink because of their relationship to a buoyant force. All objects immersed in a liquid experience a buoyant force, which pushes them upward. The strength of this force is equal to the weight of the liquid displaced, or pushed aside, by an object. Every object also experiences a downward force due to gravity, which is measured as the object's weight, and which is directly proportional to the object's mass. When the buoyant force acting on an object is greater than the downward force due to gravity, the object floats. However, when the buoyant force is less than the force due to gravity, the object sinks. Both the cork and the aluminum toy boat are able to displace enough water to create a buoyant force that exceeds the force due to gravity, so they float. However, the glass marble does not displace enough water to create a sufficient buoyant force, so it sinks.

All objects made of low-density polypropylene (LDPE) always float in water. According to Student 2, this is most likely due to which of the following reasons?

Possible Answers:

LDPE repels water effectively.

Objects made of LDPE have a shape that allows them to magnify the upward force due to surface tension that they experience.

LDPE is less dense than water.

Objects made of LDPE always displace an amount of water whose weight exceeds their own weight. 

LDPE is more dense than water.

Correct answer:

LDPE is less dense than water.

Explanation:

Student 2 says that objects can float either because their average density is less than that of water, or because they are buoyed by water's surface tension. If LDPE is less dense than water, it should always float. According to Student 2's explanation, it is also possible that objects made of LDPE are actually more dense than water, but have a shape that allows them to magnify the upward force of water's surface tension. However, the question states that all objects made of LDPE always float. If LDPE is actually more dense than water, it is very unlikely that every object made of LDPE has a shape that allows it to float. Therefore, the best explanation is more simple: “LDPE is less dense than water.”

Example Question #164 : Physics

In a physics class, students conducted a series of experiments by placing different objects into a beaker of water. They conducted twenty trials for each object. For each trial, they recorded whether or not the object floated.

First, they placed a steel paper clip into the water. They observed that the paper clip usually sank; however, they also saw that occasionally, the paper clip stayed afloat if it was placed very gently on top of the water. Next, they repeated the the same procedure using a cork, a toy boat made of aluminum, and a glass marble. They observed that both the cork and the toy boat always stayed afloat in the water, but that the glass marble always sank.

Below, three students give their explanations for these observations.

 

Student 1:

Objects float when they are less dense than the liquid in which they are immersed. For example, when immiscible liquids of varying densities are mixed together in a container, the most dense liquid will sink to the bottom of the container, while the least dense liquid will rise to the top. This same principle applies to solid objects. Because the cork and the aluminum toy boat always float, cork and the aluminum of the boat must be less dense than water. Because the glass marble always sinks, the glass of the marble must be more dense than water.

Objects that are more dense than water can also float due to surface tension. Surface tension occurs because molecules of a liquid are more attracted to each other more than they are to other objects. Molecules on the surface of water are attracted to the molecules around them and below them. This attraction causes a liquid's surface to behave if it were covered by a thin film, which resists penetration by other objects. Therefore, small objects such as paper clips can sometimes float on water when the upward force of water's surface tension exceeds the force of gravity pulling such objects down. Because the paper clips often sink and only float sometimes, we can conclude that they are indeed more dense than water, and that their floating is due to surface tension.

 

Student 2:

Objects float in two different cases: when they are buoyed by a liquid's surface tension or when their average density is less than that of the liquid in which they are immersed. The average density of cork is less than that of water. This is why the cork floats. In contrast, the density of glass is more than that of water. This is why the glass marble sinks.

However, the densities of aluminum and of steel are greater than that of water. Thus, density cannot be used to explain why the aluminum toy boat and the paper clip float. Both of these objects float because of surface tension. Because the paper clip does not have much mass, the normal upward force created by water's surface tension can be enough to allow it to float. Other objects with greater mass, like the toy boat, employ a particular shape to magnify the force of surface tension. The curved shape of the boat's bottom both stabilizes the boat and increases the amount of the boat's surface area that touches the water, maximizing the force due to surface tension that the boat receives.

 

Student 3:

In this experiment, the paper clip floats because of surface tension; however, the cork, toy boat, and marble float or sink because of their relationship to a buoyant force. All objects immersed in a liquid experience a buoyant force, which pushes them upward. The strength of this force is equal to the weight of the liquid displaced, or pushed aside, by an object. Every object also experiences a downward force due to gravity, which is measured as the object's weight, and which is directly proportional to the object's mass. When the buoyant force acting on an object is greater than the downward force due to gravity, the object floats. However, when the buoyant force is less than the force due to gravity, the object sinks. Both the cork and the aluminum toy boat are able to displace enough water to create a buoyant force that exceeds the force due to gravity, so they float. However, the glass marble does not displace enough water to create a sufficient buoyant force, so it sinks.

When a canoe is right-side up, it floats in water; however, if the canoe is overturned so that it fills with water, it sinks. Student 3 would most likely explain this observation by giving which of the following reasons?

Possible Answers:

When the canoe is right-side up, its shape allows it to displace a volume of water whose weight is greater than its own weight. When the canoe is overturned and filled with water, it no longer displaces enough water to create a sufficient buoyant force.

When the canoe is right-side up, it does not experience a downward force due to gravity. When the canoe is overturned and filled with water, a force due to gravity causes it to sink.

When the canoe is right-side up, its shape allows it to magnify the upward force due to surface tension that it experiences. When the canoe is overturned and filled with water, surface tension no longer plays a role in keeping it afloat.

When the canoe is right-side up, the buoyant force that it experiences is less than the force due to gravity that pulls it downward. When the canoe is overturned and filled with water, the buoyant force increases and exceeds the force due to gravity.

Correct answer:

When the canoe is right-side up, its shape allows it to displace a volume of water whose weight is greater than its own weight. When the canoe is overturned and filled with water, it no longer displaces enough water to create a sufficient buoyant force.

Explanation:

Student 3 says that the toy boat floats because it displaces enough water to generate a buoyant force that exceeds the force due to gravity pulling the boat down. According to Student 3, the strength of the buoyant force is equal to the weight of the water displaced by the boat. For the boat to float, the buoyant force also has to exceed the boat's weight.

We can apply this same idea to explain why the canoe floats. When the canoe is upright, the air inside the canoe helps it to displace a lot of water. When the canoe is overturned and filled with water, it no longer displaces enough water to generate enough of a buoyant force to allow it to float.

Example Question #1281 : Act Science

In a physics class, students conducted a series of experiments by placing different objects into a beaker of water. They conducted twenty trials for each object. For each trial, they recorded whether or not the object floated.

First, they placed a steel paper clip into the water. They observed that the paper clip usually sank; however, they also saw that occasionally, the paper clip stayed afloat if it was placed very gently on top of the water. Next, they repeated the the same procedure using a cork, a toy boat made of aluminum, and a glass marble. They observed that both the cork and the toy boat always stayed afloat in the water, but that the glass marble always sank.

Below, three students give their explanations for these observations.

 

Student 1:

Objects float when they are less dense than the liquid in which they are immersed. For example, when immiscible liquids of varying densities are mixed together in a container, the most dense liquid will sink to the bottom of the container, while the least dense liquid will rise to the top. This same principle applies to solid objects. Because the cork and the aluminum toy boat always float, cork and the aluminum of the boat must be less dense than water. Because the glass marble always sinks, the glass of the marble must be more dense than water.

Objects that are more dense than water can also float due to surface tension. Surface tension occurs because molecules of a liquid are more attracted to each other more than they are to other objects. Molecules on the surface of water are attracted to the molecules around them and below them. This attraction causes a liquid's surface to behave if it were covered by a thin film, which resists penetration by other objects. Therefore, small objects such as paper clips can sometimes float on water when the upward force of water's surface tension exceeds the force of gravity pulling such objects down. Because the paper clips often sink and only float sometimes, we can conclude that they are indeed more dense than water, and that their floating is due to surface tension.

 

Student 2:

Objects float in two different cases: when they are buoyed by a liquid's surface tension or when their average density is less than that of the liquid in which they are immersed. The average density of cork is less than that of water. This is why the cork floats. In contrast, the density of glass is more than that of water. This is why the glass marble sinks.

However, the densities of aluminum and of steel are greater than that of water. Thus, density cannot be used to explain why the aluminum toy boat and the paper clip float. Both of these objects float because of surface tension. Because the paper clip does not have much mass, the normal upward force created by water's surface tension can be enough to allow it to float. Other objects with greater mass, like the toy boat, employ a particular shape to magnify the force of surface tension. The curved shape of the boat's bottom both stabilizes the boat and increases the amount of the boat's surface area that touches the water, maximizing the force due to surface tension that the boat receives.

 

Student 3:

In this experiment, the paper clip floats because of surface tension; however, the cork, toy boat, and marble float or sink because of their relationship to a buoyant force. All objects immersed in a liquid experience a buoyant force, which pushes them upward. The strength of this force is equal to the weight of the liquid displaced, or pushed aside, by an object. Every object also experiences a downward force due to gravity, which is measured as the object's weight, and which is directly proportional to the object's mass. When the buoyant force acting on an object is greater than the downward force due to gravity, the object floats. However, when the buoyant force is less than the force due to gravity, the object sinks. Both the cork and the aluminum toy boat are able to displace enough water to create a buoyant force that exceeds the force due to gravity, so they float. However, the glass marble does not displace enough water to create a sufficient buoyant force, so it sinks.

Alcohol is less dense than water. Suppose that students test a piece of wood to determine if it floats in water. Then, they test it again to determine if it floats in alcohol. If Student 1's explanation is correct, the wood is __________.

Possible Answers:

equally likely to float in water and in alcohol

more likely to float in water than in alcohol

float or sink more consistently in water, and float or sink less consistently in alcohol

less likely to float in water than in alcohol

Correct answer:

more likely to float in water than in alcohol

Explanation:

According to Student 1, objects float if they are less dense than the liquid in which they are placed. We know from this question that alcohol is less dense than water. A piece of wood might be less dense than water, but it might be more dense than alcohol. So, it is possible that the wood will float in water, but sink in alcohol.

Example Question #161 : Physics

In a physics class, students conducted a series of experiments by placing different objects into a beaker of water. They conducted twenty trials for each object. For each trial, they recorded whether or not the object floated.

First, they placed a steel paper clip into the water. They observed that the paper clip usually sank; however, they also saw that occasionally, the paper clip stayed afloat if it was placed very gently on top of the water. Next, they repeated the the same procedure using a cork, a toy boat made of aluminum, and a glass marble. They observed that both the cork and the toy boat always stayed afloat in the water, but that the glass marble always sank.

Below, three students give their explanations for these observations.

 

Student 1:

Objects float when they are less dense than the liquid in which they are immersed. For example, when immiscible liquids of varying densities are mixed together in a container, the most dense liquid will sink to the bottom of the container, while the least dense liquid will rise to the top. This same principle applies to solid objects. Because the cork and the aluminum toy boat always float, cork and the aluminum of the boat must be less dense than water. Because the glass marble always sinks, the glass of the marble must be more dense than water.

Objects that are more dense than water can also float due to surface tension. Surface tension occurs because molecules of a liquid are more attracted to each other more than they are to other objects. Molecules on the surface of water are attracted to the molecules around them and below them. This attraction causes a liquid's surface to behave if it were covered by a thin film, which resists penetration by other objects. Therefore, small objects such as paper clips can sometimes float on water when the upward force of water's surface tension exceeds the force of gravity pulling such objects down. Because the paper clips often sink and only float sometimes, we can conclude that they are indeed more dense than water, and that their floating is due to surface tension.

 

Student 2:

Objects float in two different cases: when they are buoyed by a liquid's surface tension or when their average density is less than that of the liquid in which they are immersed. The average density of cork is less than that of water. This is why the cork floats. In contrast, the density of glass is more than that of water. This is why the glass marble sinks.

However, the densities of aluminum and of steel are greater than that of water. Thus, density cannot be used to explain why the aluminum toy boat and the paper clip float. Both of these objects float because of surface tension. Because the paper clip does not have much mass, the normal upward force created by water's surface tension can be enough to allow it to float. Other objects with greater mass, like the toy boat, employ a particular shape to magnify the force of surface tension. The curved shape of the boat's bottom both stabilizes the boat and increases the amount of the boat's surface area that touches the water, maximizing the force due to surface tension that the boat receives.

 

Student 3:

In this experiment, the paper clip floats because of surface tension; however, the cork, toy boat, and marble float or sink because of their relationship to a buoyant force. All objects immersed in a liquid experience a buoyant force, which pushes them upward. The strength of this force is equal to the weight of the liquid displaced, or pushed aside, by an object. Every object also experiences a downward force due to gravity, which is measured as the object's weight, and which is directly proportional to the object's mass. When the buoyant force acting on an object is greater than the downward force due to gravity, the object floats. However, when the buoyant force is less than the force due to gravity, the object sinks. Both the cork and the aluminum toy boat are able to displace enough water to create a buoyant force that exceeds the force due to gravity, so they float. However, the glass marble does not displace enough water to create a sufficient buoyant force, so it sinks.

A surfactant is a substance that reduces the surface tension of the liquid to which it is added. Laundry detergent is a surfactant. If Student 3's explanation is correct, how likely will a paper clip placed in water with laundry detergent be to float, compared to a paper clip placed in water without laundry detergent? The paper clip in water with laundry detergent is __________.

Possible Answers:

more likely to float, because it experiences a greater buoyant force

less likely to float, because it experiences less upward force due to surface tension

less likely to float, because it experiences less buoyant force

more likely to float, because it experiences a greater upward force due to surface tension

Correct answer:

less likely to float, because it experiences less upward force due to surface tension

Explanation:

According to Student 3, the paper clip floats due to water's surface tension. We also know from this question that laundry detergent reduces surface tension. So, if laundry detergent is added to water, this water will have a lower surface tension. The upward force generated by surface tension will be lower, so the paper clip will be less likely to float.

Example Question #161 : Physics

With regards to the properties of different gases, two scientists present the following statements. 

Scientist 1: Besides weight, gases' physical properties are not affected by their mass or size. All gases have the same physical properties, except under extreme conditions. For example, one million molecules of helium (a light gas) will take up as much space as one million molecules of radon (a heavy gas). This is because there is so much space between each molecule of gas that gas molecules hardly ever interact with other gas molecules in a way that is significant, causing the individual physical properties of each molecule to be irrelevant to the overall properties of the gas. 

Scientist 2: Gases will appear to have the same properties despite mass and size of individual molecules, but in fact, they do not have the exact same physical properties. While a quantity of a light gas may take up as much space as a heavy gas, the molecules of the light gas will be moving faster than the molecules of the heavier gas. Therefore, if the quantities of gases just described are allowed to flow into a new container, the lighter gas will move into that container much more quickly. Furthermore, at extremely low volumes, the space taken up by each individual molecule becomes significant enough to make a lighter gas take up a different amount of volume than a heavier gas (one with larger molecules). 

On which of the following statements would both scientists most likely agree?

Possible Answers:

Different gases occupy the same volume regardless of differences in physical properties except for in cases of very small volumes.

Without measuring weight, a heavier gas is indistinguishable from a lighter gas.

In all cases, gases of different physical properties occupy the same volume.

The speed of gas molecules depends only on mass.

The size of gas molecules affects the speed of those molecules.

Correct answer:

Different gases occupy the same volume regardless of differences in physical properties except for in cases of very small volumes.

Explanation:

The answer is "Different gases occupy the same volume regardless of differences in physical properties except for in cases of very small volumes." It is clear that Scientist 2 would agree with this claim as it was included in the statement provided by Scientist 2. Scientist 1, however, may also agree with this claim, since Scientist 1 indicates that under extreme conditions (one may consider extremely low volume to be an extreme condition) gases indeed do display different volumes. The other answers are certainly not points that both scientists can agree upon.

Example Question #163 : Physics

With regards to the properties of different gases, two scientists present the following statements. 

Scientist 1: Besides weight, gases' physical properties are not affected by their mass or size. All gases have the same physical properties, except under extreme conditions. For example, one million molecules of helium (a light gas) will take up as much space as one million molecules of radon (a heavy gas). This is because there is so much space between each molecule of gas that gas molecules hardly ever interact with other gas molecules in a way that is significant, causing the individual physical properties of each molecule to be irrelevant to the overall properties of the gas. 

Scientist 2: Gases will appear to have the same properties despite mass and size of individual molecules, but in fact, they do not have the exact same physical properties. While a quantity of a light gas may take up as much space as a heavy gas, the molecules of the light gas will be moving faster than the molecules of the heavier gas. Therefore, if the quantities of gases just described are allowed to flow into a new container, the lighter gas will move into that container much more quickly. Furthermore, at extremely low volumes, the space taken up by each individual molecule becomes significant enough to make a lighter gas take up a different amount of volume than a heavier gas (one with larger molecules). 

A gas is placed in chamber connected to another chamber by a closed valve. The valve is opened and the gas is allowed to seep into the second chamber. Which of the following gases would Scientist 2 argue would take the longest to shift into the second chamber.

Possible Answers:

Nitrogen (Atomic weight = 28 amu)

Carbon Dioxide (Atomic weight = 44 amu)

Oxygen (Atomic weight = 32 amu)

Hydrogen (Atomic weight = 1 amu)

Xenon (Atomic weight = 131 amu)

Correct answer:

Xenon (Atomic weight = 131 amu)

Explanation:

The correct answer is xenon. As Scientist 2 states, the heavier the molecule of gas, the slower the speed. Therefore, xenon, the heaviest in the answers provided, would move the slowest and therefore take the longest to move into the second chamber.

Learning Tools by Varsity Tutors