1. negligible. 2. about a tenth as much. 3. about the same. 4. more. Compared with the mass of a dozen eggs, the mass of air in an “empty refrigerator” is 1. negligible. 2. about a tenth as much. 3. about the same. 4. more. Ch 14-1

1. negligible. 2. about a tenth as much. 3. about the same. 4. more. Compared with the mass of a dozen eggs, the mass of air in an “empty refrigerator” is 1. negligible. 2. about a tenth as much. 3. about the same. 4. more. Ch 14-1 Answer: 4 One cubic meter of air at 0°C and normal atmospheric pressure has a mass of about 1.3 kilograms. A medium-sized refrigerator has a volume of about 0.6 cubic meters and contains about 0.8 kilograms of air—more than 0.75 kilograms of a dozen large eggs! We don’t notice the weight of air because we are submerged in air. If someone handed you a bag of water while you were submerged in water, you wouldn’t notice its weight either.

Consider a flexible plastic bottle containing both air and water immersed neck down in an open dish of water. The water level in the bottle will 1. fall if pinched at A but rise if pinched at B. 2. fall if pinched at A or at B. 3. fall if pinched at A but stay where it is if pinched at B. 4. rise if pinched at A but stay where it is if pinched at B. 5. stay where it is if pinched at A or at B. Ch 14-2

Consider a flexible plastic bottle containing both air and water immersed neck down in an open dish of water. The water level in the bottle will 1. fall if pinched at A but rise if pinched at B. 2. fall if pinched at A or at B. 3. fall if pinched at A but stay where it is if pinched at B. 4. rise if pinched at A but stay where it is if pinched at B. 5. stay where it is if pinched at A or at B. Ch 14-2 Answer: 3 Pinching the bottle at A compresses the air within the bottle, which pushes water out the neck of the bottle into the open dish until air pressure inside and outside the bottle is practically the same. The water level in the bottle is lowered. Pinching the bottle at B simply forces water out the neck and into the open dish, rather than rising and compressing the air above. Again, air pressure inside and outside the bottle is the same.

1. rises. 2. falls. 3. remains in place. In the presence of air, the small iron ball and large plastic ball balance each other. When air is evacuated from the container, the larger ball Ch 14-3 1. rises. 2. falls. 3. remains in place.

1. rises. 2. falls. 3. remains in place. In the presence of air, the small iron ball and large plastic ball balance each other. When air is evacuated from the container, the larger ball Ch 14-3 Answer: 2 Before evacuation, the forces acting on each ball are the gravitational force, the force exerted by the balance beam and the upward buoyant force exerted by the surrounding air. Evacuating the container removes the buoyant force on each ball. Since buoyant force equals the weight of air displaced, and the larger ball displaces the greater weight of air, the loss of buoyant force is greater for the larger ball, which falls. 1. rises. 2. falls. 3. remains in place.

Consider a Ping-Pong ball floating in a glass of water that is in an air-tight chamber. When air pressure is increased in the chamber, does the ball float lower, higher, or as before? Ch 14-4 1. Lower 2. Higher 3. As before

Consider a Ping-Pong ball floating in a glass of water that is in an air-tight chamber. When air pressure is increased in the chamber, does the ball float lower, higher, or as before? Ch 14-4 Answer: 2 The ball will float higher. The buoyancy that accounts for its flotation is due to the weight of the displaced fluid—both water and air. Higher-pressure air is denser air, and the greater weight of displaced denser air by the ball contributes to greater buoyancy by the air. This lifts the ball upward and the ball floats higher in the water. 1. Lower 2. Higher 3. As before

Consider an air-filled balloon weighted so that it is on the verge of sinking—that is, its overall density just equals that of water. Now if you push it beneath the surface, it will 1. sink. 2. return to the surface. 3. stay at the depth to which it is pushed. Ch 14-5

Consider an air-filled balloon weighted so that it is on the verge of sinking—that is, its overall density just equals that of water. Now if you push it beneath the surface, it will 1. sink. 2. return to the surface. 3. stay at the depth to which it is pushed. Ch 14-5 Answer: 1 The balloon will sink. Why? Because at deeper levels the surrounding water pressure is greater and will squeeze and compress the balloon—its density increases. Greater density results in sinking. Or look at it this way: at the surface its buoyant force is just adequate for equilibrium. When the buoyant force is reduced—it’s inadequate for equilibrium.

A pair of identical balloons are inflated with air and suspended on the ends of a stick that is horizontally balanced. When the balloon on the left is punctured, the balance of the stick is Ch 14-6 1. upset and the stick rotates clockwise. 2. upset and the stick rotates counter-clockwise. 3. unchanged.

A pair of identical balloons are inflated with air and suspended on the ends of a stick that is horizontally balanced. When the balloon on the left is punctured, the balance of the stick is Ch 14-6 Answer: 1 The end supporting the punctured balloon tips upward as it is lightened by the weight of air that escapes. Although there’s a loss of buoyant force on the punctured balloon, that decrease in upward force is less than the weight-of-air loss, since the density of air in the balloon before puncturing was greater than the density of surrounding air. 1. upset and the stick rotates clockwise. 2. upset and the stick rotates counter-clockwise. 3. unchanged.

1. the short candle. 2. the tall candle. 3. 50-50, a toss up. A short and a long candle burn in an open jar as shown. When the jar is covered the candle to go out first will be 1. the short candle. 2. the tall candle. 3. 50-50, a toss up. Ch 14-11 Thanks to Peter Hopkinson.

1. the short candle. 2. the tall candle. 3. 50-50, a toss up. A short and a long candle burn in an open jar as shown. When the jar is covered the candle to go out first will be 1. the short candle. 2. the tall candle. 3. 50-50, a toss up. Ch 14-11 Thanks to Peter Hopkinson. Answer: 2 The tall candle will go out first. Why? Because the burning candles consume oxygen and expel mainly carbon dioxide. You might guess that the denser dioxide would settle to the bottom of the jar and snuff out the shorter candle. It would if it weren’t so warm. Being much warmer than it is denser, it rises to snuff the taller candle first.

1. larger. 2. smaller. 3. the same size. Water with air bubbles flows through a pipe that becomes narrower. In the narrow region the water gains speed and the bubbles are 1. larger. 2. smaller. 3. the same size. Ch 14-12 Thanks to Paul Doherty.

1. larger. 2. smaller. 3. the same size. Water with air bubbles flows through a pipe that becomes narrower. In the narrow region the water gains speed and the bubbles are 1. larger. 2. smaller. 3. the same size. Ch 14-12 Thanks to Paul Doherty. Answer: 1 As water gains speed, pressure in the water decreases, in accord with Bernoulli’s principle. Decreased water pressure squeezes less on air bubbles, allowing them to expand—so that air pressure and surrounding water pressure match. If the flowing water continues its flow into a wider section of pipe, speed decreases, pressure increases, and the bubbles become smaller.

1. Bernoulli’s principle 2. Newton’s laws 3. Both You’re driving in a convertible car with the top up and the windows closed. You note that the fabric top puffs up. To explain this interesting phenomenon you invoke 1. Bernoulli’s principle 2. Newton’s laws 3. Both Ch 14-13

1. Bernoulli’s principle 2. Newton’s laws 3. Both You’re driving in a convertible car with the top up and the windows closed. You note that the fabric top puffs up. To explain this interesting phenomenon you invoke 1. Bernoulli’s principle 2. Newton’s laws 3. Both Ch 14-13 Answer: 1 In accord with the principle of continuity, a fluid gains speed when it flows into a constricted region. Your car, convertible or otherwise, somewhat constricts the flow of moving air, so air moving over the top speeds up. What happens to the pressure in a fluid when it gains speed? Bernoulli’s principle provides the answer: pressure decreases. Reduced atmospheric pressure on the top of the fabric with no reduction in air pressure beneath, inside the car, produces a pressure difference on the fabric and it puffs upward. Cheers for Bernoulli!