Net Force and Motion - Middle School Physical Science
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What is the formula to compute acceleration from net force and mass?
What is the formula to compute acceleration from net force and mass?
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$a = \frac{F_{net}}{m}$. Rearrange $F_{net} = ma$ by dividing both sides by $m$.
$a = \frac{F_{net}}{m}$. Rearrange $F_{net} = ma$ by dividing both sides by $m$.
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Identify the direction of acceleration relative to the direction of $F_{net}$.
Identify the direction of acceleration relative to the direction of $F_{net}$.
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Acceleration is in the same direction as $F_{net}$. Newton's Second Law: force and acceleration vectors align.
Acceleration is in the same direction as $F_{net}$. Newton's Second Law: force and acceleration vectors align.
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What is the SI unit of force, and what base units equal it?
What is the SI unit of force, and what base units equal it?
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Newton; $1\ \text{N} = 1\ \text{kg}\cdot\text{m}/\text{s}^2$. Force unit honors Isaac Newton; derived from $F=ma$.
Newton; $1\ \text{N} = 1\ \text{kg}\cdot\text{m}/\text{s}^2$. Force unit honors Isaac Newton; derived from $F=ma$.
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Which quantity changes when a nonzero net force acts on an object: speed, velocity, or both?
Which quantity changes when a nonzero net force acts on an object: speed, velocity, or both?
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Velocity (speed and/or direction) changes. Force changes velocity; speed is just magnitude of velocity.
Velocity (speed and/or direction) changes. Force changes velocity; speed is just magnitude of velocity.
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What happens to an object's motion when $F_{net} = 0$?
What happens to an object's motion when $F_{net} = 0$?
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No acceleration; velocity stays constant (may be $0$). Newton's First Law: no net force means no change in motion.
No acceleration; velocity stays constant (may be $0$). Newton's First Law: no net force means no change in motion.
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What is the best definition of net force on an object?
What is the best definition of net force on an object?
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The vector sum of all forces acting on the object. Net force combines all individual forces as vectors.
The vector sum of all forces acting on the object. Net force combines all individual forces as vectors.
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Which option describes unbalanced forces on an object?
Which option describes unbalanced forces on an object?
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Forces do not cancel so $F_{net} \ne 0$. Unequal forces produce a nonzero net force.
Forces do not cancel so $F_{net} \ne 0$. Unequal forces produce a nonzero net force.
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What is the formula for Newton's Second Law relating net force, mass, and acceleration?
What is the formula for Newton's Second Law relating net force, mass, and acceleration?
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$F_{net} = ma$. Newton's Second Law: force equals mass times acceleration.
$F_{net} = ma$. Newton's Second Law: force equals mass times acceleration.
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Calculate $F_{net}$ when a $10\ \text{N}$ force right and $6\ \text{N}$ force left act on an object.
Calculate $F_{net}$ when a $10\ \text{N}$ force right and $6\ \text{N}$ force left act on an object.
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$4\ \text{N}$ to the right. Subtract opposing forces: $10-6=4$ N rightward.
$4\ \text{N}$ to the right. Subtract opposing forces: $10-6=4$ N rightward.
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Which calculation finds average acceleration from velocity data over a time interval?
Which calculation finds average acceleration from velocity data over a time interval?
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$a = \frac{\Delta v}{\Delta t}$. Acceleration is change in velocity over time.
$a = \frac{\Delta v}{\Delta t}$. Acceleration is change in velocity over time.
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Identify the best conclusion if data show $a$ increases linearly as $F_{net}$ increases for the same cart.
Identify the best conclusion if data show $a$ increases linearly as $F_{net}$ increases for the same cart.
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$a$ is directly proportional to $F_{net}$ for constant $m$. Linear relationship confirms Newton's Second Law.
$a$ is directly proportional to $F_{net}$ for constant $m$. Linear relationship confirms Newton's Second Law.
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From data: $F_{net}=8\ \text{N}$ gives $a=2\ \text{m}/\text{s}^2$. What is the mass?
From data: $F_{net}=8\ \text{N}$ gives $a=2\ \text{m}/\text{s}^2$. What is the mass?
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$4\ \text{kg}$. Rearrange $F_{net} = ma$: $m = \frac{8}{2} = 4$.
$4\ \text{kg}$. Rearrange $F_{net} = ma$: $m = \frac{8}{2} = 4$.
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Two trials use the same net force: mass doubles. What happens to $a$?
Two trials use the same net force: mass doubles. What happens to $a$?
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Acceleration is cut in half. From $a = \frac{F_{net}}{m}$: doubling $m$ halves $a$.
Acceleration is cut in half. From $a = \frac{F_{net}}{m}$: doubling $m$ halves $a$.
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A graph shows $a$ vs. $F_{net}$ for constant mass. What does the slope represent?
A graph shows $a$ vs. $F_{net}$ for constant mass. What does the slope represent?
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$\frac{1}{m}$. From $a = \frac{F_{net}}{m}$, slope equals $\frac{1}{m}$.
$\frac{1}{m}$. From $a = \frac{F_{net}}{m}$, slope equals $\frac{1}{m}$.
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Two trials use the same object: $F_{net}$ doubles. What happens to $a$ if mass stays constant?
Two trials use the same object: $F_{net}$ doubles. What happens to $a$ if mass stays constant?
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Acceleration doubles. From $a = \frac{F_{net}}{m}$: doubling $F_{net}$ doubles $a$.
Acceleration doubles. From $a = \frac{F_{net}}{m}$: doubling $F_{net}$ doubles $a$.
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A graph shows $F_{net}$ vs. $a$ for constant mass. What does the slope represent?
A graph shows $F_{net}$ vs. $a$ for constant mass. What does the slope represent?
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$m$. From $F_{net} = ma$, slope equals mass.
$m$. From $F_{net} = ma$, slope equals mass.
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Calculate acceleration for $m = 2\ \text{kg}$ and $F_{net} = 10\ \text{N}$.
Calculate acceleration for $m = 2\ \text{kg}$ and $F_{net} = 10\ \text{N}$.
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$5\ \text{m}/\text{s}^2$. Apply $a = \frac{F_{net}}{m} = \frac{10}{2} = 5$.
$5\ \text{m}/\text{s}^2$. Apply $a = \frac{F_{net}}{m} = \frac{10}{2} = 5$.
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Calculate net force for $m = 3\ \text{kg}$ and $a = 4\ \text{m}/\text{s}^2$.
Calculate net force for $m = 3\ \text{kg}$ and $a = 4\ \text{m}/\text{s}^2$.
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$12\ \text{N}$. Apply $F_{net} = ma = 3 \times 4 = 12$.
$12\ \text{N}$. Apply $F_{net} = ma = 3 \times 4 = 12$.
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Which option describes balanced forces on an object?
Which option describes balanced forces on an object?
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Forces cancel so $F_{net} = 0$. Equal and opposite forces result in zero net force.
Forces cancel so $F_{net} = 0$. Equal and opposite forces result in zero net force.
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Identify the direction of acceleration compared with the direction of $F_{net}$.
Identify the direction of acceleration compared with the direction of $F_{net}$.
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Acceleration is in the same direction as $F_{net}$. Force and acceleration are vectors pointing the same way.
Acceleration is in the same direction as $F_{net}$. Force and acceleration are vectors pointing the same way.
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What does it mean if the net force on an object is $0\ \text{N}$?
What does it mean if the net force on an object is $0\ \text{N}$?
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No acceleration; velocity is constant (may be $0$). Zero net force means no change in motion per Newton's first law.
No acceleration; velocity is constant (may be $0$). Zero net force means no change in motion per Newton's first law.
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Find the net force: $6\ \text{N}$ east and $6\ \text{N}$ west act on an object.
Find the net force: $6\ \text{N}$ east and $6\ \text{N}$ west act on an object.
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$0\ \text{N}$. Equal opposite forces cancel out completely.
$0\ \text{N}$. Equal opposite forces cancel out completely.
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What is the formula for net force when forces act along one line?
What is the formula for net force when forces act along one line?
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$F_{net} = \sum F$. Sum all forces acting in the same line to find the net force.
$F_{net} = \sum F$. Sum all forces acting in the same line to find the net force.
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Find the net force: $8\ \text{N}$ right and $3\ \text{N}$ left act on an object.
Find the net force: $8\ \text{N}$ right and $3\ \text{N}$ left act on an object.
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$5\ \text{N}$ right. Subtract opposing forces: $8-3=5$ N in the right direction.
$5\ \text{N}$ right. Subtract opposing forces: $8-3=5$ N in the right direction.
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What is the formula for net force in terms of mass and acceleration?
What is the formula for net force in terms of mass and acceleration?
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$F_{net} = ma$. Newton's second law states net force equals mass times acceleration.
$F_{net} = ma$. Newton's second law states net force equals mass times acceleration.
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