A narrow boat, such as a canoe, kayak, or racing shell, is like a long cylinder that can rotate about a horizontal axis (see figure). When the boat's occupants are seated, its overall center of gravity is below the rotation axis and the boat is upright and stable. When someone stand up, however, the boat's center of gravity shifts above the rotation axis and the boat tips over. Why does this center gravity shift cause the boat to become unstable?

You inflate a rubber balloon with oxygen and then release it. The balloon flies around the room until it is empty and deflated. What pushed the balloon forward?

You live in a two-story house with identical bathrooms on the ground floor and second floor. You turn on the showers in both bathrooms. How do the water pressures before each shower nozzle and the water speeds after each nozzle compare?

You drop an unopened metal can of soup and it lands bottom-first on the floor. When you inspect the can, you see that it has dented outward in places. Where did it dent outward and why?

You are riding a roller coaster and your speed is increasing as you plunge downhill on the first hill. Your acceleration is directed

A birdfeeder hangs motionless from a tree branch on a long string. After a bird disturbs it, the birdfeeder swings back and forth below the branch before settling back to its original stable equilibrium position. Why is the birdfeeder's equilibrium position stable?

A spaceship is moving at constant velocity toward a distant star. The ship experiences no gravitational forces. To maintain its velocity, the ship must have its rocket engines

A spacecraft is moving eastward in a circular orbit 200 miles above the Earth's equator. It is time for the spacecraft to return to the ground. The most effective way to cause the spacecraft to begin descending toward the Earth's surface is to fire its rocket engine. In which direction should the engine direct its rocket exhaust?

The exposed air ducts in warehouses and gymnasiums are often several feet in diameter. If a wide duct and a narrow duct are delivering the same amount of air each second, the fan pushing air through the wide duct consumes less power than the fan pushing air through the narrow duct. Why?

Doctors use a centrifuge to separate red blood cells from blood plasma. The centrifuge swings a container of blood at high speed in a circular path. The red bloods drift away from the center of the circle, leaving the blood plasma nearer the center. Describe the pressures and densities in the blood as the centrifuge swings it in a circle.

A log is floating motionless on a calm lake, with about half the log located beneath the water level. It's a sunny day and the temperature of the air increases, although the air pressure remains constant. How does the air's increasing temperature affect the log?

The oil and vinegar in a salad dressing tend to separate, with the oil floating on the vinegar. Suppose an herb in the dressing sits motionless at the interface where the oil and vinegar meet. Describe the average density of that herb.

You hold an unopened glass bottle of root beer upright in one hand and pound its bottle cap downward hard with a rubber mallet. As a consequence of this action,

Suppose a soccer ball is approaching your leg at 30 km/h and your leg is moving toward the soccer ball at 30 km/h. What is the fastest the soccer ball can possibly travel after it hits your leg? [You can assume perfect (ideal) bouncing behaviors for the ball and your leg.]

You are inflating a limp plastic balloon with helium. The pressure inside the balloon remains atmospheric pressure, even as more helium accumulates inside the balloon. How do the balloon's total weight and the buoyant force on the balloon change during this filling process?

The roller coaster you are riding is going through a loop-the-loop at high-speed. At the moment when you are at the top of the loop, you and your car are inverted yet you feel an apparent weight directed toward the sky. At this moment, your acceleration is

A bicycle touches the ground at only two points, forming a base of support that is a line. As the bicycle (including the rider) moves forward, it steers itself automatically so that it

A horizontal pipe bends toward the right. As water flows steadily through this pipe, what happens as the water starts to travel around the bend?

Water is flowing at constant velocity through a straight, horizontal pipe. The pressure at the entry end of the pipe is greater than the pressure at the exit end of the pipe. What would happen if those two pressures suddenly became equal?

Why does a sprinter lean forward as she picks up speed at the start of a race?

A pressure washer is used to clean stone surfaces. Its pump delivers high-pressure water to a hose and that water is sprayed through a nozzle so this travels through the air and hits the stone surface. Which of the following correctly describes the water's pressure?

Suppose a rocket is launched vertically, so that its velocity always points vertically upward. By the time the rocket's fuel runs out, its altitude is 200 miles above the Earth's surface and its speed is approximately zero. What happens to the rocket after its fuel runs out?

Firefighters are battling a fire on the 10th floor of an apartment building. When they stand on the ground, their fire hose can only shoot the water steadily up to the 8th floor. They carry the nozzle end of that fire hose to the top of a 4-story-tall ladder and again point the nozzle upward. Their fire hose can now shoot the water steadily up to which floor?

A scuba tank is a metal bottle that can be filled with air and used to supply that air to a person who is underwater. Suppose you fill a scuba tank with air until the particle density in the tank is 100 times the particle density of the surrounding air. At room temperature, what are the density and pressure of the air inside that tank?

You and your friend are riding a carousel. Your horses are side-by-side and your friend is closer to the center of the carousel than you are. As the carousel turns steadily, which of the following is true?

You heat your metal water bottle on a stovetop until it is filled with hot air at atmospheric pressure. You then seal the bottle and set it on the kitchen counter to cool. Assume the bottle doesn't change size (volume) throughout this process. During the cooling process, what happens to the density and pressure of the air in the bottle?

You are riding a train that is moving straight ahead at high speed. The train comes to a curve in the tracks and begins to turn toward the left. You find yourself pressed against the right side of your seat. What force, if any, is pushing you toward the right?

After heavy rains, the water flowing down a nearby river is turbulent, also known as "white water." During a drought, however, the water flowing down that same river is laminar; it appears smooth and clear. Explain the difference.

Some fire extinguishers use spray carbon dioxide. The mass of a carbon dioxide molecule is about 50% greater than the mass of an average air molecule. At room temperature, a liter of carbon dioxide

You kick a soccer ball through the air. From the ball's perspective, air is flowing northward toward the ball. Describe the air pressures on the ball's south side and east side (see figure).