Unit 3: Energy — Heat, Light, and Sound
Where the energy around you actually goes: heat moving between objects, light bouncing and bending, and sound shaking through the air.
13 topics · 45 questions
Each topic is a path, not a menu: work down it in order and every question builds on the one above. Click any of them to watch the answer draw itself.
Forms of Energy
- How it worksHow does stored potential energy turn into moving kinetic energy the instant you let go?
- Common mistakeWhy isn't energy something you can see sitting inside an object like a liquid in a bottle?
- Ties togetherHow does a swinging pendulum show energy trading back and forth between potential and kinetic the whole time?
Your turn1 of 2
A stretched rubber band and a rock sitting at the top of a hill are both completely still. Do they both still count as having energy?Heat vs. Temperature
- How it worksHow does temperature measure how fast particles jiggle while heat measures the total energy moving between them?
- Common mistakeWhy doesn't a metal spoon actually feel colder than a wooden spoon sitting at the exact same temperature?
- Going furtherWhat happens to the temperature of two objects left touching each other for a long time?
Your turn1 of 2
A huge pot of lukewarm soup and one tiny drop of boiling water. Which one holds more total heat ENERGY?Conduction
- How it worksHow does heat energy hop from one jiggling particle to the next particle touching it in conduction?
- Worked exampleFind how much faster heat moves through a metal pan than a wooden spoon handle if metal conducts heat about 400 times faster than wood.
- Common mistakeWhy doesn't heat ever flow from a cold object into a hot one on its own?
Your turn1 of 2
Find how many times faster heat moves through a metal pan than a wooden spoon handle if metal conducts heat about 379 times faster than wood.Convection
- How it worksHow does warm air rising and cool air sinking set up a circling convection current?
- How it worksWalk me through how convection currents inside a pot of boiling water carry hot water up and cool water down.
- Common mistakeWhy isn't convection the same thing as conduction, even though both move heat?
- Going furtherWhat happens to convection currents in a pot of soup the moment you turn off the stove?
Your turn1 of 2
Why does the air near the ceiling of a heated room always feel warmer than the air by your feet?Radiation
- How it worksHow does radiation carry heat energy as waves that don't need any particles to travel through?
- Common mistakeWhy doesn't radiation need air or any material at all to carry heat, unlike conduction and convection?
- Going furtherWhat happens to how much heat a dark black shirt absorbs from sunlight compared to a white shirt?
Your turn1 of 2
You can feel the sun's heat on your face even though there's empty space between you and the sun. How does that heat cross the emptiness of space?Insulators and Conductors of Heat
- How it worksHow does trapped air inside an insulator like foam or feathers slow conduction almost to a stop?
- Common mistakeWhy doesn't cold actually flow in through your window, rather than heat flowing out?
- Going furtherWhat happens to a hot drink in a foam cup compared to the same drink in a metal cup after ten minutes?
Your turn1 of 2
A puffy winter coat keeps you warm even though it isn't producing any heat of its own. How does it actually work?How Light Travels
- How it worksHow does light travel in perfectly straight lines called rays until something gets in the way?
- Worked exampleFind how long it takes light to cross a 3 meter classroom if light travels about 300000 kilometers every second.
- Common mistakeWhy doesn't light bend around an object the way sound bends around a corner?
Your turn1 of 2
Find how long it takes light to cross a 15 meter classroom if light travels about 300,000,000 meters every second.Reflection
- How it worksHow does a mirror bounce light back at the exact same angle it arrived at?
- Common mistakeWhy doesn't a mirror actually flip left and right, even though your reflection seems reversed?
- Going furtherWhat happens to a reflection when a smooth mirror is replaced with a bumpy, crumpled piece of foil?
Your turn1 of 2
How does a mirror bounce light back at you?Refraction
- How it worksHow does light bend when it slows down crossing from air into water?
- Worked exampleFind which bends light more, going from air into water or from air into glass, if glass slows light down more than water does.
- Common mistakeWhy isn't the straw actually broken, even though refraction makes it look bent?
- Going furtherWhat happens to light passing through a curved lens instead of a flat piece of glass?
Your turn1 of 2
Glass slows light down more than water does. Does light bend MORE going from air into glass, or from air into water?Color and How We See
- How it worksHow does an object's surface absorb every color of light except the one it bounces back to your eyes?
- How it worksWalk me through how your eye and brain turn incoming light into the colors you actually see.
- Common mistakeWhy doesn't a red shirt actually contain any red dye that leaks color into your eyes?
- Going furtherWhat color does a red apple appear under a light that only shines pure green?
Your turn1 of 2
Why does a red apple look red in sunlight, when sunlight actually contains every color mixed together?Shadows
- How it worksHow does an object blocking light create a dark shadow shaped by the angle the light comes from?
- Worked exampleFind how a shadow's length changes as the sun moves from low in the sky to directly overhead.
- Common mistakeWhy isn't a shadow a real thing that gets cast onto the ground, rather than just blocked light?
Your turn1 of 2
As the sun moves from low in the sky up to directly overhead, what happens to the length of your shadow?Sound: Vibrations, Pitch, and Volume
- How it worksHow does a vibrating object push and pull the air into sound waves that reach your ear?
- How it worksWalk me through how a fast vibration makes a high pitch and a slow vibration makes a low pitch.
- Worked exampleFind whether a guitar string vibrating 220 times a second or one vibrating 440 times a second makes the higher pitch.
- Common mistakeWhy doesn't a louder sound automatically mean a higher pitched sound?
- Going furtherWhat happens to a rubber band's pitch when you stretch it tighter before plucking it?
Your turn1 of 2
Find the pitch frequency, in vibrations per second, of the HIGHER-pitched guitar string, if one vibrates 239 times a second and the other vibrates 495 times a second.How Sound Travels
- How it worksHow do vibrating particles bump into their neighbors to carry a sound wave through a solid, liquid, or gas?
- Worked exampleFind how many football fields sound crosses in one second if sound travels about 340 meters every second.
- Common mistakeWhy can't sound travel at all through the empty vacuum of space?
- Going furtherWhat happens to how fast sound travels when it moves through water instead of air?
Your turn1 of 2
Find how many football fields (about 100 meters each) sound crosses in 7 seconds if sound travels about 340 meters every second.