Physical Science II
Fluid Physics Review
Name_____________________
Period ____________________
Conceptual Questions
1. What are the three common states of matter?
Solid, Liquid and Gas
2. Which state of matter has a definite volume and shape?
Solid
3. Which state of matter has a definite volume, but takes on the shape of its container?
Liquid
4. Which state of matter takes on both the shape and volume of its container?
Gas
5. What is considered a fluid?
Liquids and Gasses
6. Why is it more comfortable to sit on a chair versus gymnasium bleachers?
The chair has a larger surface area to support your body, so it reduces the amount of pressure
that is exerted on your body.
7. What are the units of Pressure?
Pascal’s (can be written as Pa)
8. As you travel higher in the Earth’s atmosphere, what happens to the air pressure?
The air pressure gets lower as you travel higher in the Earth’s atmosphere.
9. As a submarine dives deeper in the ocean, what happens to the pressure?
The pressure gets larger as you dive deeper in a fluid.
10. Why can you survive the 100,000 Pa of air pressure that is currently pressing on your body?
Your body is exerting an equal outward pressure to balance against the inward pressure of the
atmosphere.
11. What device is used to measure air pressure?
Barometer.
12. How can a barometer be used to predict the weather?
If the barometer is reading a changing air pressure it indicates that the weather is changing.
When the barometer reading is rising, the weather is generally going to be clear. If the reading
is falling, then it is likely that a rain or thunderstorm is approaching.
13. What does Pascal’s Principle say about the pressure in a fluid?
The fluid pressure in a closed container is transmitted equally throughout the entire fluid and
also against the walls of the container.
14. What is a buoyant force?
It is the upward force that acts on an object that is immersed in a fluid.
15. How does the buoyant force affect your body when you are in a swimming pool?
The buoyant force acts upward against your body weight, so it seems that you are lighter
when in the pool.
16. How can you determine the buoyant force acting on an object?
1) Collect the water that is displaced by the object and measure the weight of that displaced
water. The buoyant force is equal to the weight of the displaced water.
2) Use a force sensor to measure the weight of an object in the air and then to measure the
weight of the object in the fluid. The difference in those two weights is the buoyant force.
17. What determines whether or not an object will sink or float?
The density of the object compared to the density of the fluid. If the object is more dense, it
will sink. If the fluid is more dense, it will float.
18. If an object is floating on the surface of a liquid, what can you determine about the buoyant force?
The buoyant force must be exactly the same as the weight in order for the object to float.
19. Why can a plane fly on Earth, but it would not be able to fly on the moon?
The flight of a plane depends on the motion of the air (a fluid) around the wings. There is no air
on the moon, so flight would not be possible.
20. What are the four forces that act on an airplane during flight?
Lift, Thrust, Drag and Weight
21. Explain what lift is and how it affects an airplane.
Lift is an upward force that pushes the plane into the sky. The lifting force is what allows the
plane to travel upwards, away from the Earth’s surface.
22. What is thrust and how does it affect the motion of an airplane?
Thrust is the forward force that is provided by the engines of the plane. The thrust is responsible
for moving the plane at a high enough speed to generate lift under the wings.
23. Explain how drag affects an airplane.
Drag is also known as air resistance and it acts against the forward motion of the plane, trying to
slow it down.
24. How is the weight of the plane related to its ability to fly?
The weight of the plane is pulling it toward the ground. In order for the plane to fly, the thrust
must be great enough to generate a lifting force that is larger than the weight. As long as lift is
larger than weight the plane will be able to fly.
25. How do lift and thrust interact with one another during flight?
The thrust is what creates the airspeed to generate lift. Without any thrust, there could be no lift.
Problems
26. The wind is blowing into a 2.0m × 1.25m glass window with a force of 150 N. How much pressure is
being applied to the window by the wind?
𝑃=
𝐹
𝐴
𝑃=
150𝑁
(2.0𝑚 ×1.25𝑚)
𝑃 = 60 𝑃𝑎
27. A boat with a surface area of 10m2 is exerting a pressure of 150 Pa on the water. How much does
this boat weigh?
𝑃=
𝐹
𝐴
150 𝑃𝑎 =
𝐹
10𝑚2
𝐹 = 1,500 𝑁
28. What is the area of a piston that is exerting a 5,000 Pa of pressure with a force of 1000 N?
𝑃=
𝐹
𝐴
5,000 𝑃𝑎 =
1000𝑁
𝐴
𝐴 = 0.2 𝑚2
29. A hydraulic system is operated by two pistons. Piston 1 has an area of 0.005 m2. Piston 2 has an area
of 0.50 m2. What force would need to be exerted on Piston 1 in order for Piston 2 to lift a 10,000 N
weight?
𝐹1
𝐴1
=
𝐹2
𝐹1
𝐴2
0.005𝑚2
=
10,000𝑁
0.50𝑚2
𝐹1 = 100𝑁
30. A hydraulic lift in an auto body shop uses 500 N of force on a 0.05m2 cylindrical piston to lift a
30,000 N car. What is the area of the piston that is lifting the car?
𝐹1
𝐴1
=
𝐹2
500𝑁
𝐴2
0.05𝑚2
=
30,000𝑁
𝐴2
𝐴2 = 3𝑚2