Physical Science Lesson 6 and Quiz 6

Archimedes' Principle

An object immersed in a fluid experiences an upward buoyant force caused by constant interactions with the surrounding fluid. The strength of this force equals the weight of the displaced fluid.

Pressure

How much force is applied to a certain area or, in mathematical terms, P = F/A, where P is the pressure, F is the force, and A is the area over which the force acts.

a. The pressures are all the same

In the picture below, there are 4 containers. The pressure is measured at the bottom of each container. If you put them in order of increasing pressure (smallest first, largest last) what is the correct order? a. The pressures are all the same b. 4, 3, 2, 1 c. 1, 2, 3, 4 d. 4 is smallest, but the others are the same. e. You cannot tell without knowing the volumes of the containers.

Pressure at a given depth is independent of _____. (Rules for unbounded fluids)

Pressure at a given depth is independent of direction.

Pressure depends on ___ and is greater at greater ____. (Rules for unbounded fluids)

Pressure depends on depth and is greater at greater depth.

Pressure is always _______ to the surface of a submerged object (Rules for unbounded fluids)

Pressure is always perpendicular to the surface of a submerged object

Pressure is the same for all points at the ____ ____. (Rules for unbounded fluids)

Pressure is the same for all points at the same depth.

A

Which picture best shows the direction of the force the water exerts on the side of a swimming pool:

buoyant force

a force pushing upward on objects immersed in a fluid

How big was the buoyant force on the cylinder? _____ Newtons a. 9 newtons b. 20 newtons c. 29 newtons d. 49 newtons

a. 9 newtons

How much did the displaced water weigh? ______Newtons a. 9 newtons b. 20 newtons c. 29 newtons d. 49 newtons

a. 9 newtons

What happens if you change the shape of the container? a. Nothing b. The pressure is higher when the width of the fluid is wider c. The pressure is lower when the width of the fluid is wider d. It depends

a. Nothing

What will happen if you replace the woman with a man who weighs twice as much? a. The pressure will increase b. The pressure will remain the same c. The pressure will decrease

a. The pressure will increase

What would happen if even a child with a weight of 60 pounds stood on the platform with a sharp point (having an area of 0.1 square inches)? a. The pressure will increase b. The pressure will remain the same c. The pressure will decrease

a. The pressure will increase

What happens when the pressure gauge is moved up and down in the water? When the gauge is deeper in the water, the pressure is a. higher b. lower c. the same d. it depends

a. higher

A person gets into the boat. As the boat sinks deeper into the water, what happens to the pressure on the bottom surface of the boat? Select one: a. it increases b. it decreases c. it remains the same

a. it increases

What happens to the pressure on the block as it is pushed deeper into the water? Select one: a. it increases. b. it decreases. c. it stays the same. d. it changes from upward to zero e. it changes from upward to downward

a. it increases.

Pressure is the same in __ ___. (unbounded fluids)

all directions

density

an objects mass divided by it's volume density = mass/volume

Fluid

anything that flows. This refers to gases such as air and liquids such as water

The wall of a weather balloon has two forces on it, pressure from the air inside the balloon pushing out and pressure from the air outside the balloon pushing in. What will happen to the balloon as it is released and it rises in the atmosphere? a. It will get smaller because of the increased force on the outside of the balloon. b. It will get larger because of the decreased force on the outside of the balloon. c. It will stay the same size. Newton's Third Law says that the forces from the air inside and outside the balloon must be equal.

b. It will get larger because of the decreased force on the outside of the balloon.

A partially submerged object is in uniform motion (it is not moving). Therefore, the forces on it must be balanced. As your textbook explains, a boat will sink into the water until it displaces enough water so that the weight of displaced water equals the boat's weight. What will happen if you add some weight to the boat? a. It will raise up in the water. b. It will sink deeper in the water. c. It will stay at the same depth.

b. It will sink deeper in the water.

You have three equal size blocks which weigh 5 Newtons, 8 Newtons, and 10 Newtons. A volume of water equal to the volume of the blocks weights 7 Newtons. Mark which of the blocks will sink? a. The block weighing 5 Newtons b. The block weighing 8 Newtons c. The block weighing 10 Newtons

b. The block weighing 8 Newtons c. The block weighing 10 Newtons

What will happen if you also double the area of the platform at the same time as you double the weight, i.e. go from the woman on the 5 in22 platform to the man on the 10 in22 platform? a. The pressure will increase b. The pressure will remain the same c. The pressure will decrease

b. The pressure will remain the same

A heavy rock is lying under water on the bottom of a swimming pool. Which of the following is correct? Select one: a. The rock is harder to lift when it is under water than it would be on dry land because the water pressure pushing down on it helps hold it down. b. The rock is easier to lift when it is under water than it would be on dry land because the buoyant force of the water pushing on the rock helps to push it upward. c. It requires no more force to lift a rock under water than it does on dry land, and also it requires no less force--the situation is the same in either case. d. The rock is significantly easier to lift when it is under water because its actual weight is less in water--the earth pulls on it differently. e. The rock is significantly harder to lift when it is under water because the buoyant force acts in addition to its weight, making a greater force necessary.

b. The rock is easier to lift when it is under water than it would be on dry land because the buoyant force of the water pushing on the rock helps to push it upward.

You drop a rock in a stream and note that it sinks to the bottom. From this you can conclude that a. The rock weighs the same as the water it displaces. b. The rock weighs more than the water it displaces. c. The rock weighs less than the water it displaces.

b. The rock weighs more than the water it displaces.

If a block of wood floats with half its volume submerged, Select one: a. the buoyant force is equal to half the weight of the block. b. the weight of the block is the same as that of the displaced water. c. the volume of the block is the same as that of the displaced water. d. the buoyant force is equal to twice the weight of the displaced water. e. the buoyant force is equal to twice the weight of the block.

b. the weight of the block is the same as that of the displaced water.

If liquids are wholly contained they are called ____

bounded

What happened to the weight of the cylinder when it was submerged in water? a. It went up. b. It went down. c. It stayed the same. d. It is impossible to tell. e. Both B and C are true.

c. It stayed the same.

A fluid pushes _____ everywhere on a submerged object.

inward

What will happen if a solid object has a lesser density that the fluid in which it is placed?

it will float.

What will happen if a solid object has a greater density (or more mass per cm) than the fluid in which it is placed?

it will sink

You can figure out if an object will sink or float by determining the ___ ____ on a submerged or partially submerged object.

net force

Pressure is always ____ to the surface of a submerged object (or to the walls of the container) (unbounded fluids)

perpendicular

Any object submerged in a fluid experiences ____ from the fluid.

pressure

Fluids that lack boundaries are one or more sides, like the oceans or the atmosphere are called ____

unbounded

Fluids can be ___ or ____ contained

wholly or partially contained

The ____ the difference between the density of the object and the density of the fluid the higher the object will float.

greater

Now this same block of wood that was floating with one half of its volume out of the water is pushed down so that it is completely underneath the water. Which of the following statements is correct? Select one: a. The buoyant force on the block is the same in the two cases because the weight per unit volume of the wood has not changed. b. The buoyant force on the block is the same in the two cases because the weight per unit volume of the water is the same in each case. c. The buoyant force on the block is greater when the block is completely submerged than it is when the block is floating. d. The buoyant force on the block is greater when it is floating than when it is totally submerged. e. The buoyant force on the block is the same in the two cases because the block loses weight as it is submerged.

c. The buoyant force on the block is greater when the block is completely submerged than it is when the block is floating.

What happens when the gauge is moved sideways, but the depth is kept the same? a. The pressure goes up b. The pressure goes down c. The pressure stays the same d. It depends

c. The pressure stays the same

Convection

circulation in a fluid caused by temperature and density differences

The boat from the question above springs a leak and sinks completely. What happens to the buoyant force? Select one: a. The buoyant force on the boat does not change because the weight per unit volume of the material it is made of has not changed. b. The buoyant force on the boat does not change because the weight per unit volume of the water is the same in each case. c. The buoyant force on the boat is greater when the boat is completely submerged than it is when the boat is floating. d. The buoyant force on the boat is smaller because it doesn't displace as much water after it sinks. e. The buoyant force on the boat does not change because the boat weighs less when it is submerged.

d. The buoyant force on the boat is smaller because it doesn't displace as much water after it sinks.

In convection currents, warmer air rises and cooler air descends. Which of the following is correct? Select one: a. There is a buoyant force on the warmer air, but there is not a buoyant force on the cooler air. b. The gravitational force pulls harder on each kilogram of cooler air than it does on a kilogram of warmer air. c. The buoyant force on the warmer air is upward, while the buoyant force on the cooler air is downward. d. The warmer air has a lower density than the cooler air which it displaces. e. The warmer air has a higher density than the cooler air which it displaces.

d. The warmer air has a lower density than the cooler air which it displaces.

Predict the pressure of the woman with a weight of 120 pounds standing on a small platform of area 5 square inches. a. 5 b. 120 c. 5x120=6000 d. 5/120=0.04 e. 120/5=24

e. 120/5=24

Pressure

forces exerted by fluids pressure = force/area