A gymnast is performing a somersault in midair. While she is not touching anything, which of the following physical quantities is not changing with time? [neglect any effects due to the air]

You are so excited that you high-five a massive bronze statue. Your hand was moving at 1 meter-per-second before hitting the statue's hand, but comes to a complete stop after the impact. If the statue had been wearing a soft wool mitten and your hand had come to a complete stop on that mitten, how would that have affected the momentum your hand transferred to the statue (and mitten) during this impact?

A blue car is stuck in the mud and a red car is trying to pull it out with a bungee cord that connects the red car to the blue car. As the red car moves forward, the bungee cord stretches and then breaks, but the blue car never moves at all. Which car(s) provided the energy that broke the bungee cord?

When you drop a bouncy ball on a hard cement sidewalk, the ball bounces almost to its original height. When you drop that same ball on a soft sand beach, the ball barely bounces at all. Why does the ball bounce so differently from the two surfaces?

When its wireless key is nearby, your new car starts at the push of a button. You accidently place the key on the car's roof, start the car, and drive forward. The key slides off the back of the car and falls to the ground. Why did the key do that?

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?

You are making pizza for a party and you throw a spinning disk of pizza dough into the air. What happens to the disk's angular momentum and angular velocity as the disk stretches and its diameter increases? [Assume nothing is touching the spinning disk and neglect any effects due to the air]

When 1 one-pound bird rests motionless on a horizontal tree branch, the branch bends downward 1 inch from its empty position. When 4 one-pound birds rest motionless on that same branch, how far does the branch bend downward from its empty position? [Assume the branch behaves like a spring]

You are standing on a balcony, 80 meters above the sidewalk, when you accidently bump a flowerpot. The flowerpot begins to fall and it will hit the sidewalk in 4 seconds if you don't act swiftly. A childhood accident left you with super-speed, so you race downstairs and catch the flowerpot after it has been falling for only 2 seconds. How far above the sidewalk is the flowerpot when you catch it?

When you walk onto a springboard at the diving center and settle motionless, the board will have bent downward 4 inches from its empty position. You do some gentle bouncing and soon it is bent downward 8 inches from its empty position. What is your acceleration when the board is bent downward 8 inches?

You get on your bicycle near the top of a long, smooth hill. After a moment of motionlessness, you start rolling downhill faster and faster. You did not use the pedals, so what caused the bicycle wheels to start turning?

A seesaw is balanced, with its center of gravity located exactly at its pivot. The seesaw is

You want to look your best during the royal wedding. As part of your training, you have a book balanced on your head as you walk horizontally at constant velocity. You are doing

You let go of a rope and drop straight down onto a trampoline. You bounce. During your initial descent from the rope, you accelerate downward until the moment when you

A vertical flagpole is at equilibrium in calm air and it stands perfectly straight and motionless. A sudden gust of wind causes the flagpole to sway back and forth about equilibrium. As the flagpole sways, when is its speed greatest and when is its acceleration greatest?

A hammer's weight acts in the downward direction, yet you can use the hammer to pound a nail into the ceiling. Why?

You trying to get into a pirate's treasure chest, but are have trouble turning the rusty old lock. What must happen for the motionless lock to begin rotating in the direction that opens it?

A bartender is new to the job and slides two mugs of root beer toward the end of the bar much too fast. The mugs slide off the bar side-by-side at the same instant and soon hit the floor. At the moment the two mugs slid off the bar, one mug weighed twice as much as the other, but the lighter mug was moving twice as fast as the heavier mug. What happened?

You accidently drop a raw egg on a massive granite countertop and the egg shatters. During its impact, did the egg transfer significant energy or momentum to that countertop?

You are pushing a book away from you and it is sliding across your desk at a constant horizontal velocity. How does your force on the book compare with the frictional force that the desk exerts on the book? [Consider only horizontal forces]

You stand motionless on a spring scale and it is correctly reporting your weight. You suddenly jump upward. During that jump, while you are still in contact with the scale and you are accelerating upward, what force is the scale exerting on you?

A speedboat is pulling a water skier across the water and that skier is traveling in a straight path at a steady speed. The net force experienced by the water skier

You are in San Francisco, riding a cable car up a steep hill. The car's speed is steady and it is moving in a constant uphill direction. What force is the cable car exerting on you?

After you serve a volleyball, the ball is traveling in an arc over the net. While nothing is touching the ball, which of the following quantities is constant? [Neglect effects due to the air.]

Suppose a soccer ball is approaching your leg at 20 km/h and your leg is moving toward the soccer ball at 20 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.]

To win a prize at the fair, you must knock a massive block off a shelf by hitting that block with a ball. Assuming all the balls have the same mass and you throw them with equal forward speeds, which of these four balls will transfer the most forward momentum to the block?

You're at the lake and watch two children jump off a dock at the same time. They both kick equally hard during their jumps, but one child jumps mostly upward while the other child jumps mostly forward. After they leave the dock,

A box of groceries sits motionless on a long wooden board. As you slowly lift one end of the board, so that it becomes a ramp, but the box remains in place. You keep increasing the steepness of the ramp until suddenly the box begins to slide down the ramp. Why did the box begin to move?

The smooth, flat surface of a ramp is tilted so that one end of the ramp is higher than the other. When a ball is on that ramp, the ball's

You and your friend each carry a 1-liter bottle of water in your right hand from the first floor to the fifth floor. The two bottles started and finished motionless and side-by-side. If you walked up the stairs to the fifth floor and your friend took the elevator, which of you did more work on your water bottle?