Download Chapter 4 Forces and fluids

Chapter 4 Forces and fluids

1.What two things must you know to calculate the pressure exerted on a surface?

A.
B.
C.
D.
the force and the weight of the object
the force and the area over which it is applied
the force that is applied and the density of the surface
the area over which a force is applied and the mass of the object
applying the pressure
Feedback: Sometimes the force exerted is the weight of an object, which is the object's
mass multiplied by its acceleration due to gravity.

2.A __________ is any substance that has no definite shape and can flow.
A. solid
B. plasma
C.
fluid
D. gas
Feedback: A fluid takes the shape of its container.

3.Which is the SI unit of pressure?
A. Newton
B. watt
C. ampere
D.
Pascal
Feedback: One Pascal (Pa) is a small unit, so pressure is sometimes expressed in
units of kPa, which is 1,000 Pa.

4.In which direction is pressure by a fluid exerted on an object that is submerged in it?
A.
B.
C.
D.
upward
downward
perpendicular to all surfaces of the object
parallel to the vertical surfaces, perpendicular to the horizontal
surfaces
Feedback: The pressure on each side of a submerged object is perpendicular to the
surface of the object, and the size of the pressure depends only on the object's depth in
the fluid.

5.As the height of a fluid above a surface __________, the pressure exerted by the fluid
on that surface __________.
A.
B.
C.
D.
increases, increases
increases, decreases
decreases, increases
The pressure exerted by a fluid on a surface is unaffected by the
height of the fluid.
Feedback: Assuming the container is unchanged, increasing the height of the fluid is
accomplished by adding more fluid, and therefore more weight, to the container.
Because P = F ÷ A, increasing the weight of the fluid (which increases the force that the
fluid applies) also increases the pressure that the fluid exerts on the bottom of the
container.

6.What is the approximate pressure exerted on your body by the atmosphere at sea
level?
A. 100 Pa
B. 1,000 Pa
C. 10,000 Pa
D.
100,000 Pa
Feedback: Your body is filled with fluids that exert pressure outward and balance the
pressure exerted by the atmosphere.

7.The supporting force exerted by a fluid on an object immersed in it is called
__________.
A. lift
B. density
C. viscosity
D.
buoyant force
Feedback: The amount of buoyant force on an object in a fluid determines whether it
will sink or float.

8.What determines whether an object will sink or float?
A. whether a buoyant force acts on the object
B.
whether the buoyant force is larger than the object's weight
C. the direction of the buoyant force on the object
D. whether gravity acts on the object in the fluid
Feedback: Whether an object sinks or floats depends on whether the buoyant force is
larger than its weight. The buoyant force is greater when the surface of the object that is
in contact with the fluid is greater.

9.Archimedes' principle states that __________.
A.
the buoyant force on an object is equal to the weight of the fluid it
displaces
B. the buoyant force on an object is greater than the weight of the fluid it
displaces
C. when the speed of a fluid increases, the pressure exerted by the fluid
decreases
D. pressure applied to a fluid is transmitted unchanged throughout the
fluid
Feedback: If an ice cube is placed in a full glass of water and causes it to overflow, the
weight of the displaced water would be equal to the buoyant force on the ice cube.

10.The __________ of an object is the mass of an object divided by the volume it
occupies.
A. weight
B.
density
C. malleability
D. conductivity
Feedback: Any object that has a density greater than the density of a fluid it is placed in
will sink.

11.According to Pascal, pressure applied to a fluid __________.
A. decreases as it moves through the fluid
B. increases as it moves through the fluid
C.
is transmitted unchanged throughout the fluid
D. fluctuates as it is transmitted throughout the fluid
Feedback: According to Pascal, pressure applied to a fluid is transmitted unchanged
throughout the fluid. The force can be increased by increasing the area.

12.The area of the small piston in a hydraulic system is 1 m2. The area of the larger
piston is 4 m2. If a force of 10 N is applied to the small piston, what is the force available
in the large piston?
A. 4 N
B. 10 N
C.
40 N
D. 400 N
Feedback: According to Pascal, pressure applied to a fluid is transmitted unchanged
throughout the fluid. Therefore, the ratio of force to area must be the same in both
pistons.

13.A(n) __________ uses a fluid to increase an applied force.
A. simple machine
B. compound machine
C. wheel and axle
D.
hydraulic system
Feedback: The fluid enclosed in a hydraulic system transfers force from one piston to
another.

14.Bernoulli's principle states that as the velocity of a fluid __________, the pressure
exerted by the fluid __________ .
A. increases, increases
B.
increases, decreases
C. decreases, decreases
D. decreases, increases
Feedback: This property of fluids enables airplanes to rise into the air.

15.How does Bernoulli's principle explain how airplanes fly?
A.
B.
C.
Air pressure is greater below the wings, creating lift.
Air pressure is greater on the top of the wings, creating lift.
The air pressure on top of the wing is equal and opposite to the air
pressure on the bottom, creating a balanced upward force.
D. The backward force exerted by an engine creates an equal and
opposite push, resulting in lift.
Feedback: According to Bernoulli's principle, when the speed of a fluid increases, the
pressure exerted by the fluid decreases. In an airplane wing, air flows faster over the
top than the bottom, decreasing the pressure on the top of the wing. This produces an
unbalanced upward force, creating lift.