Use the concept of pressure to explain why snowshoes are betterthan regular shoes for

Describe the four phases of matter. Compare their external, observable properties. Compare the nature of the forces between atoms or molecules (or both) in the solid, liquid, and gas phases.

What is the difference between a mixture of two elements and a compound formed from the two elements?

If you classify everything around you as an element, a compound, or a mixture, which category would have the largest number of entries?

Why can gases be compressed much more readily than solids or liquids?

Suppose you are in the International Space Station in orbit around Earth and a fellow astronaut gives you what appears to be an inflated balloon. Describe how you could determine whether the balloon contains a gas, a liquid, or a solid.

Use the concept of pressure to explain why snowshoes are better than regular shoes for walking in deep snow.

Why is it that a person can lay still on a bed of nails (see Figure 4.51) without suffering any serious injuries but would incur severe puncture wounds to his feet if he tried to stand bare- foot on the same bed?

Bicycle tires are often inflated to pressures as high as 75 psi, whereas automobile tires, which must support much heavier loads, are pumped to only 32 psi. Why is that? Explain.

The same bicycle tire pump is used to inflate a mountain bike tire to 40 psi and then a road bike tire to 100 psi. What difference would the user notice when using the pump on the two tires? crew member suggests pumping water from the river into an empty

Explain the difference between gauge pressure and absolute pressure.

How can you use the volume of some quantity of a pure sub- stance to calculate its mass? crew member suggests pumping water from the river into an empty

The mass density of a mixture of ethyl alcohol and water is 950 kg/m3 . Is the mixture mostly water, mostly alcohol, or about half and half? What is your reasoning?

Believe it or not, canoes have been made out of concrete (and they actually float). But even though concrete has a lower density than aluminum, a concrete canoe weighs a lot more than an aluminum one of the same size. Why is that?

Would the weight density of water be different on the Moon than it is on Earth? What about the mass density?

The way pressure increases with depth in a gas is different from the way it does in a liquid. Why?

Workers are to install a hatch (door) near the bottom of an empty storage tank. In choosing how strong to make the hatch, does it mat- ter how tall the tank is? How wide it is? Whether it is going to hold water or mercury? Explain.

If the acceleration from gravity on Earth suddenly increased, would this affect the atmospheric pressure? Would it affect the pressure at the bottom of a swimming pool? Explain

If Earths atmosphere warmed up and expanded to a larger total vol- ume but its total mass did not change, would this affect the atmo- spheric pressure at sea level? Would this affect the pressure at the top of Mount Everest? Explain.

Is there a pressure variation (increase with depth) in a fuel tank on a spacecraft in orbit? Why or why not?

Explain how a barometer can be used to measure altitude.

Why does the buoyant force always act upward?

What substances would sink in gasoline but float in water?

It is easier for a person to float in the ocean than in an ordinary swimming pool. Why?

A ship on a large river approaches a bridge, and the captain notices that the ship is about a foot too tall to fit under the bridge. A crew member suggests pumping water from the river into an empty tank on the ship. Would this help?

In The Unparalleled Adventure of One Hans Pfaall by Edgar Allen Poe, the hero discovers a gas whose density is 37.4 times less than that of hydrogen. How much better at lifting would a balloon filled with the new gas be compared to one filled with hydrogen?

A brick is tied to a balloon filled with air and then tossed into the ocean. As the balloon is pulled downward by the brick, the buoyant force on it decreases. Why?

Venuss atmosphere is much more dense than Earths whereas that of Mars is far less dense. Suppose it is decided to send a probe to each planet that, once it arrived, would be carried around in the planets atmosphere by a helium-filled balloon. How would the size of each balloon compare to the size that would be needed on Earth?

What is Pascals principle?

How does a cars brake system make use of Pascals principle?

What important thing happens when the speed of a moving fluid increases?

The pressure in the air along the upper surface of an aircrafts wing (in flight) is lower than the pressure along the lower surface. Com- pare the speed of the air flowing over the wing to that of the air flowing under the wing.

How does a perfume atomizer make use of Bernoullis principle?

When two trains, going in opposite directions, are passing on tracks that are laid out close together, the train cars can often be seen to be leaning in toward one another where they are in proximity. How might the air passing through the narrow gap separating the two trains contribute to the observed attraction between their cars?

Corrugated plastic pipes are commonly used to carry water away from the foundation areas of houses. These accordion-like pipes typically vary in diameter, alternating between smaller and larger widths, at regular intervals of a few centimeters or so, making them much more flexible than straight plastic pipes. Assuming the water in such pipes undergoes steady flow, describe the variations in the speed and pressure of the water as it moves along.

36. Explain why a smoothly flowing stream of water from a faucet often gets progressively narrower in cross-section as the water falls (see Figure 4.52).

A grain silo is filled with 2 million pounds of wheat. The area of the silos floor is 400 ft2 . Find the pressure on the floor in pounds per square foot and in psi.

A bicycle tire pump has a piston with area 0.44 in.2 . If a person exerts a force of 30 lb on the piston while inflating a tire, what pres- sure does this produce on the air in the pump?

A large truck tire is inflated to a gauge pressure of 80 psi. The total area of one sidewall of the tire is 1,200 in.2 . What is the outward force on the sidewall because of the air pressure?

The water in the plumbing in a house is at a gauge pressure of 300,000 Pa. What force does this cause on the top of the tank inside a water heater if the area of the top is 0.2 m2 ?

A box-shaped metal can has dimensions 8 in. by 4 in. by 10 in. high. All of the air inside the can is removed with a vacuum pump. Assuming normal atmospheric pressure outside the can, find the total force on one of the 8-by-10-in. sides.

A viewing window on the side of a large tank at a public aquarium measures 50 in. by 60 in. ( Figure 4.53). The average gauge pres- sure from the water is 8 psi. What is the total outward force on the window? Figure 4.53 Problem 6.

7. A large chunk of metal has a mass of 393 kg, and its volume is mea- sured to be 0.05 m3 (a) Find the metals mass density and weight density in SI units. (b) What kind of metal is it?

A small statue is recovered in an archaeological dig. Its weight is measured to be 96 lb, and its volume 0.08 ft3 . (a) What is the statues weight density? (b) What substance is it? 36,198 ft. What is the gauge pressure at this depth?

A large tanker truck can carry 20 tons (40,000 lb) of liquid. (a) What volume of water can it carry? (b) What volume of gasoline can it carry?

The total mass of the hydrogen gas in the Hindenburg zeppelin was 18,000 kg. What volume did the hydrogen occupy?

A large balloon used to sample the upper atmosphere is filled with 900 m3 of helium. What is the mass of the helium?

A certain part of an aircraft engine has a volume of 1.3 ft3. (a) Find the weight of the piece when it is made of iron. (b) If the same piece is made of aluminum, what is its weight? Determine how much weight is saved by using aluminum instead of iron.

The volume of the Drop Tower Bremen (a 100-meter-tall tube used to study processes during free fall) is 1,700 m3 . (a) What is the mass of the air that must be removed from it to reduce the pressure inside to nearly zero (1 Pa compared to 100,000 Pa)? (b) What is the weight of the air in pounds?

It is determined by immersing a crown in water that its volume is 26 in.3 0.015 ft3. (a) What would its weight be if it were made of pure gold? (b) What would its weight be if its volume were half gold and half lead?

Find the gauge pressure at the bottom of a swimming pool that is 12 ft deep.

The depth of the Pacific Ocean in the Mariana Trench is 36,198 ft. What is the gauge pressure at this depth?

Calculate the gauge pressure at a depth of 300 m in seawater.

A storage tank 30 m high is filled with gasoline. (a) Find the gauge pressure at the bottom of the tank. (b) Calculate the force that acts on a square access hatch at the bot- tom of the tank that measures 0.5 m by 0.5 m.

The highest point in North America is the top of Mount McKinley in Alaska, 20,320 ft above sea level. Using Figure 4.29, find the approximate air pressure there.

The highest altitude ever reached by a glider (as of this writing) is 14,938 m. What is the approximate air pressure at that altitude?

An ebony log with volume 12 ft3 is submerged in water. What is the buoyant force on it?

An empty storage tank has a volume of 1,500 ft3 . What is the buoy- ant force exerted on it by the air?

A blimp used for aerial camera views of sporting events holds 200,000 ft3 of helium. (a) How much does the helium weigh? (b) What is the buoyant force on the blimp at sea level? (c) How much can the blimp lift (in addition to the helium)?

A modern-day zeppelin holds 8,000 m3 of helium. Compute its maximum payload at sea level.

A box-shaped piece of concrete measures 3 ft by 2 ft by 0.5 ft. (a) What is its weight? (b) Find the buoyant force that acts on it when it is submerged in water. (c) What is the net force on the concrete piece when it is underwater?

erged in water. (a) What is its weight? (b) What is the buoyant force acting on it? (c) What is the size and the direction of the net force on it?

The volume of an iceberg is 100,000 ft3 ( Figure 4.54). (a) What is its weight, assuming it is pure ice? (b) What is the volume of seawater it displaces when floating? (Hint: You know what the weight of the seawater is.) (c) What is the volume of the part of the iceberg out of the water?

A boat (with a flat bottom) and its cargo weigh 5,000 N. The area of the boats bottom is 4 m2 . How far below the surface of the water is the boats bottom when it is floating in water?

A scale reads 100 N when a piece of aluminum is hanging from it. What does it read when it is lowered so that the aluminum is sub- merged in water?

A rectangular block of ice with dimensions 2 m by 3 m by 0.2 m floats on water. A person weighing 600 N wants to stand on the ice. Would the ice sink below the surface of the water?

The wing of an airplane has an average cross-sectional area of 12 m2 and experiences a lift force of 75,000 N. What is the average difference in the air pressure between the top and bottom of the wing?

When exactly 1 cup of sugar is dissolved in exactly 1 cup of water, less than 2 cups of solution result. Why?

Near the end of Section 4.3, we stated that, because the gram was defined to be the mass of 1 cm3 of water, the density of water is exactly 1,000 kg/m3 . Verify this.

What would be the mass density, weight density, and specific gravity of aluminum on the Moon? The acceleration of gravity there is 1.6 m/s2

Earths mass is 6 1024 kg, and its radius is 6.4 106 m. What is the average mass density of Earth? The density of the rocks com- prising Earths outermost layer (its crust) ranges from 2,000 to 3,500 kg/m3 . Based on your answer, what can you conclude about the material deep inside Earths interior?

In 1993, a football coach in the United States accused an opposing teams punter of using a football inflated with helium instead of air. Estimate how much lighter a football would be if inflated to a gauge pressure of 1 atm with helium instead of air. The volume of a foot- ball is approximately 0.1 ft3.

Two swimming pools are 8 ft deep, but one measures 20 ft by 30 ft, and the other measures 40 ft by 60 ft. Identical drain valves at the bottom of each pool are 10 in.2 in area. Compare the force on each valve.

Scuba divers take their own supply of air with them when they go underwater. Why couldnt they just take a long hose with them from the surface and breathe through it ( Figure 4.55)?

A motorist driving through Colorado checks the tire pressure in Denver (elevation 5,000 ft) and then again at the Eisenhower Tunnel (elevation 11,000 ft). Would the pressures be the same? What two main factors affect the tire pressure as the car climbs?

A glass contains pure water with ice floating in it. After the ice melts, will the water level be higher, lower, or the same? (Ignore evapora- tion.)

<!--td {border: 1px solid #ccc;}br {mso-data-placement:same-cell;}-->At one point in the novel Slapstick by Kurt Vonnegut, the force of gravity on Earth suddenly increased tremendously. The result: . . . elevator cables were snapping, airplanes were crashing, ships were sinking, motor vehicles were breaking their axles, bridges were collaps- ing, and on and on. Would a ship really sink if the force of gravity were increased?

A brick rests on a large piece of wood floating in a bucket of water. The brick slides off and sinks. Does the water level in the bucket go up, go down, or stay the same?

As a helium balloon rises up in the air, work is done on it against the force of gravity. What is doing the work? What energy transfer or transformation is taking place?