When you stand in front of an open refrigerator, trying to decide which flavor of Ben and Jerry's to eat, you feel cold even though no chilled air actually touches your skin. The reason you feel cold is that

You are visiting a playground and you notice that a girl on one swing completes each full cycle of motion in much less time than a boy on another swing. The girl has a much shorter period of motion (time between cycles) than the boy because

You are standing in the middle of a level subway car that is moving forward at constant velocity when another passenger accidentally spills an enormous container of olive oil. Suddenly, the floor cannot exert any frictional forces on your feet. Because nothing else is touching you, you

You are eating at an outdoor restaurant on a cold day and the restaurant has a red hot heating element positioned about 10 feet above you that keeps you surprisingly warm. Heat from that element reaches you

Just mixing gasoline and air together won't make them burst into flames because

A juggler tosses a club straight up. Disregarding any effects due to the air, what force or forces are acting on the club while it is above the juggler's hands?

Wrapping a hot potato in aluminum foil helps keep the potato warm because the shiny aluminum foil is

To transform 1 kilogram of boiling-hot water at 100 °C into 1 kilogram of steam at 100 °C, you must

Flowing honey is less likely to become turbulent than flowing water because

Water is flowing gently out of the end of a garden hose. You block off most of the hose's opening with your thumb and now the water sprays out at high speed because you

The first kind of perpetual motion machine provides an inexhaustible supply of mechanical work (or the equivalent of work), but consumes nothing at all from its environment, not even heat. An example would be a black box that consumes nothing yet provides electricity forever. This form of perpetual motion machine is impossible because it

A seemingly "haunted" house emits creaking sounds as it cools off at night. Since sound carries energy, the house must obtain that energy from somewhere (other than ghosts and goblins). While this energy begins as thermal energy, the sound doesn't appear until the outside temperature drops well below the temperature of the house because

When a liquid flows through a collection of stationary obstacles, its flow can be smooth and laminar, or it can be swirling and turbulent. The liquid's flow is more likely to become turbulent if you increase its

Moments before it's ignited by the sparkplug, the mixture of fuel and air inside an automobile engine cylinder is compressed to very high density. During the compression process, the mixture's

The hotter it is outside, the more electric energy an air conditioner must use to remove each joule of heat from the 72 °F indoor air in your home. It must consume more electric energy on a hotter day because

You are pulling your niece uphill on a sled and the sled experiences a small downhill frictional force as it slides uphill on the snow. Your niece is traveling in a straight line at a constant speed. The net force your niece is experiencing is

You wake up one very cold winter morning to find the grass outside covered with frost. How did this ice form on the grass?

You throw a curve ball that is bending toward your right as it travels away from you. It is able to bend in this manner because

You are rearranging your room and are now sliding your desk across the floor at constant velocity. Which of the following statements about the forces acting on the desk is correct? [Consider only horizontal forces.]

You make a sharp left turn in your car and your cellphone slips off the dashboard and out the right passenger window. The cellphone leaves the car because

As the water stream from a fountain rises upward in the open air, its gravitational potential energy increases,

You are tossing popcorn straight up and catching it in your mouth. At the moment each piece of popcorn reaches its peak height, its velocity is

At high altitude, a commercial jetliner must compress the outside air before circulating it in the pressurized cabin. The compressed air must first be sent through an air conditioner, however, because compressing air

As an orchestra warms up, the wind instruments (e.g., flutes, clarinets, oboes) and the air inside them actually become hotter. These instruments have openings and are not sealed. How does this warming process affect the average pressure and density of the air inside the wind instruments?

You are cleaning the siding on your house by spraying water at it from a hose and nozzle. At the center of the stream of water, right where it hits the siding, the water is coming to a complete stop. The pressure in the water at the center of the stream as it touches the siding is

A rigid two-blade wind turbine that is experiencing zero net torque

You and your friend carry identical water bottles from the first floor to the fifth floor. You start side-by-side and you finish side-by-side, but one of you uses the stairs while the other climbs straight up a ladder. Which of you did the most work on your water bottle?

Ice cubes gradually shrink in a frost-free freezer because

As heat flows from hot soup to a cold kitchen, the entropy (disorder) of the soup

Tightening a guitar string

Two children are balanced on a seesaw, but one child weighs twice as much as the other child. The heavier child is sitting half as far from the pivot as is the lighter child. Since the seesaw is balanced, the heavier child is exerting on the seesaw

If you blow carefully across the top of a drinking straw, it will emit a tone. If you now close off the bottom of the straw with your finger, the tone that it emits will

The three nonflammable objects in your hand are identical except that one is black, one is white, and one is shiny. You place them in a roaring fire and soon they have the same temperature: 1800 °C. They remain solid. Which one is glowing most brightly?

Your table at a family-style restaurant has a "lazy Susan" in the middle. This large circular platform rotates frictionlessly so that you can "pass" an entree to your friends by placing it on the platform and then rotating the platform. When the server places a new entree on the platform, it

You're at the lake and watch two children jump off a dock. They jump at the same time and at the same speed, but the boy jumps mostly upward while the girl jumps mostly forward. After they leave the dock,

The second kind of perpetual motion machine provides an inexhaustible supply of mechanical work (or the equivalent of work), but consumes only heat from its constant-temperature environment. An example would be a black box that absorbs heat from the 70 °F room air and converts that heat into electricity forever. This form of perpetual motion machine is impossible because it

You are practicing tennis alone by hitting a tennis ball forward toward a cement wall. Each time the ball hits the wall, it bounces backward at high speed so that you can hit it again. During its bounce, the ball

You are carrying a child on your back as you walk down a hill. The child is traveling straight at a steady speed. In which direction is the force you are exerting on the child?

You are standing in a slow-moving stream, facing upstream so that the water is coming toward the front of your body. You are wearing shorts and the water level is slightly above your bare knees. The water experiences perfect laminar flow around each of your nearly cylindrical legs. You measure the water pressure at a specific altitude below your right knee and find that the water pressure is

Running on soft dry sand is exhausting, so you switch to running on hard wet sand. The hard wet sand removes less energy from you because

If you strike a stiff, spring-like surface with a mallet and listen to the sound it emits, you'll notice that this sound is more complicated than that emitted by a string or a thin bar. That's because surfaces

A hot air balloon is passing over your head when the pilot turns on the flame and heats up the air inside the balloon's envelope (the balloon's fabric skin). That envelope is open at the bottom, where the flame heats it. As the temperature of the air inside the unsealed envelope increases, the

A dog and a cat jump horizontally off a wall at the same moment and soon land on the level horizontal field that extends outward from the base of the wall. The dog weighs twice as much as the cat, but the cat was moving forward horizontally twice as fast as the dog when the two animals left the wall. In this situation,

When water rushing through a fire hose flows around a bend in that hose, its pressure changes. The water pressure

In the game of shuffleboard, you push plastic disks forward and then release them so that they slide across a level playing surface. Once you release a disk, you are no longer pushing and it gradually skids to a stop. Its final position determines your score. As each disk skids to a stop, what becomes of the kinetic energy it had when you released it? That energy is

You add a teaspoon of salt to a glass of pure water. The salt initially sits at the bottom of the water, but it slowly dissolves so that eventually you have a glass of salt water. Which has more entropy: the glass of pure water with salt sitting at its bottom or the glass of salt water?

You are pulling a wagon full of children up a hill at constant velocity. Which one of the following statements is true?

A cross-country skier is struggling to get up a hill, so you offer to help. As the skier passes you, you reach out with your hand and exert an uphill force of 80 N (18 pounds) on the skier. When you do this, the skier exerts

A gust of wind shakes your home and causes a hanging chandelier to begin swinging gently back and forth on its support chain. When its overall motion is small, the time it takes the chandelier to complete one full oscillation of that motion (its period of oscillation) does not depend on

A skateboarder rides swiftly up the edge of a bowl-shaped surface and leaps into the air. While in the air, the skateboarder flips upside and tosses the skateboard from hand to hand. The skateboarder then rides safely back down the bowl. During the time that the skateboarder and skateboard are not touching anything, one aspect of their motion that is constant is their total (or combined) [note: neglect any effects due to the air]

How is a steam engine able to obtain work (ordered energy) from hot steam?

You and several friends take turns bungee jumping from Beta Bridge, using the same spring-like bungee cord. Near the end of your turn, you bounce gently up and down on the cord with a period (the time it takes for each bounce) of 1 second. One friend has your same height, but is heavier than you. Another friend has your same weight, but is shorter than you. During your friends' turns, what are the periods of their bounces?

It is a beautiful summer day and the residents of a high-rise apartment building are eating dinner on their balconies. A resident accidentally knocks an empty glass off a balcony that is about 80 meters (260 feet) above the cement patio. The glass would have smashed on that patio after falling for 4 seconds, however, a quick-witted resident catches the glass after it has fallen for only 2 seconds. How far above the patio was the glass when it was caught?

You are at the gym, exercising on a step machine. You have one foot on each of the machine's pedals and you move those pedals up and down as you step. The pedals always push upward on your feet, but they push upward harder on your feet while moving downward than they do while moving upward. When during this exercise is your foot transferring energy to the pedal that it is touching?

You take off your shoes to sneak quietly into your home late at night. Unfortunately, it's too dark to see the concrete block your friend left on the floor and your big toe collides with it. The block doesn't move and your foot comes to a complete stop due to the impact. Luckily, you are wearing soft woolen socks because when your foot stops during the impact, your toe transfers

Suppose a musician is playing a wind instrument (e.g., a flute, clarinet, or oboe) and the density of the air suddenly decreases. There is no change in the air's pressure or in how the musician is playing the instrument. What happens to the instrument's sound?

Two puppies are fighting over a toy. Each puppy grips one end of that toy in its mouth and pulls. Suddenly, the puppy on the right pulls especially hard on the toy and moves its end of the toy to the right. The other puppy manages to keep its end of the toy from moving. Alas, the toy breaks and the game ends. Breaking the toy required energy and that energy was provided

When wood burns in air, the water and carbon dioxide molecules that form as the result of combustion reactions have

You are swinging a bucket full of water around you in a big horizontal circle at a constant speed. You are at the center of its circular path. The net force on the bucket points directly

You are trying to set the world's record for drinking water through the tallest drinking straw. What could you do to have the best chance of setting this record?