AP Physics 2 : Turbulence
Study concepts, example questions & explanations for AP Physics 2
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Example Questions
Example Question #1 : Fluid Dynamics
Turbulent flow is characterized by __________.
low flow rates
irregular and chaotic flow
regular streamlines
All of these
irregular and chaotic flow
Turbulent flow is caused by sufficiently high flow rates, and is characterized by chaotic and irregular flow patterns. Streamlines represent the curves tangent to the point of the direction of flow; thus, if a flow is turbulent the streamlines will be chaotic as well.
Example Question #1 : Turbulence
Which of the following is an example of turbulent flow?
The flow of water through a hose
Pouring olive oil into a pan
The flow of water in the center of a calm stream
The wisps of smoke from a blown-out candle
The wisps of smoke from a blown-out candle
The wisps of smoke from a blown out candle start out a smooth, but eventually swirl and become chaotic and turbulent. The other examples can be intuitively thought of as smooth flow, and thus are laminar.
Example Question #4 : Fluid Dynamics
Methanol is traveling through a cylindrical tube with a diameter of 
We will use the expression for Reynold's number for this problem:
Where 
Rearranging for velocity:
For laminar flow:
Plugging in our values into the expression, we get:
Methanol has a relatively low viscosity, so it only has a very small range for laminar flow and quickly becomes turbulent
Example Question #3 : Fluid Dynamics
What is the Reynold's number of water flowing through a circular tube of diameter 
Assume 
We will use the expression for Reynold's number for this problem:
Where 
Plugging in our values, we get:
Example Question #2 : Turbulence
What is the Reynold's number of water flowing through a fully filled rectangle duct that is 
Assume 
None of the other answers
We will use the expression for Reynold's number for this problem:
For a fully filled rectangular duct, the hydraulic diameter is:
Plugging in values:
Now we can plug our values into the original expression:
Example Question #1 : Turbulence
Honey is flowing through a rectangular duct with width 
We will use the expression for Reynold's number for this problem:
Rearranging for hydraulic diameter, we get:
For a partially filled rectangular duct, the expression for hydraulic diameter is:
Rearranging for height:
Example Question #1 : Turbulence
By what factor does the Reynolds's number change for water flowing through a circular tube as the cross-sectional area of the tube gradually triples?
Let's begin with the expression for Reynold's number:
Dividing the second expression by the first, we get:
From the problem statement, we are told:
Also, for a circular tube:
Therefore:
Now we need to determine the change in velocity. From the law of continuity, we know that:
Rearranging:
Where:
Thus:
Plugging in expressions (2) and (3) into (1), we get:
Example Question #1 : Turbulence
A baseball is thrown at a catcher with a high velocity and the ball passes right by the glove of the catcher. Which of the following scenarios will occur because of this?
The ball will be pulled toward the glove because of the decreased air pressure.
None of these situations will occur.
The ball will be pulled toward the glove because of the increased air pressure.
The ball will be pushed away from glove because of the increased air pressure.
The ball will be pushed away from glove because of the decreased air pressure.
The ball will be pulled toward the glove because of the decreased air pressure.
As the baseball passes by the glove, the air surrounding the glove increases in velocity. The increase in air velocity will cause a decrease in pressure. The decrease in pressure causes the ball to be pulled towards the glove.
Therefore the correct answer is that the ball will be pulled toward the glove because of the decreased air pressure.
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