energy pathways
A lamp is on for 10 minutes. Which energy form is useful, and which is wasted? Explain.
Useful: Light | Wasted: Thermal
Claim: “If something makes sound, sound energy must come first.” True or false? Why?
False; sound comes from another energy like mechanical
Why do moving objects eventually stop even without a push?
Mechanical energy changes to thermal due to friction
Two toys use identical batteries. One makes light, one makes motion. What energy is the same at the start?
Chemical energy
A machine moves forever without energy input. Possible or impossible? Why?
Impossible; energy is always transformed and lost
A battery-powered fan is running. List the energy forms in order and circle where energy begins to be lost.
Chemical → Electric → Mechanical → Thermal (loss begins at motion)
Claim: “Light bulbs only use light energy.” Identify the mistake.
They use electric energy and also produce thermal energy
A machine feels hot after working. What does this reveal about efficiency?
Some energy was wasted as thermal
A candle and a flashlight both make light. Why are their starting energies different?
Candle: chemical | Flashlight: chemical → electric
A device turns all energy into useful motion with no heat. Possible? Explain.
Impossible due to friction
A phone is charging while playing music. Name two parallel energy pathways happening at the same time.
Electric → Chemical (charging) AND Electric → Sound/Thermal
Claim: “If energy is lost, it disappears.” Correct this using science language.
Energy is transformed, often into thermal energy
Two ramps are identical except surface texture. Which causes faster energy loss and why?
Rough ramp; more friction → more thermal energy
Two speakers use the same electricity. One is louder. What energy factor changed?
Amount of sound energy transferred
A system produces sound without motion. Possible? Justify.
Impossible; sound needs vibrations (motion)
A rolling ball hits a pillow instead of the floor. How does this change the energy pathway?
More mechanical energy converts to thermal; less sound than hitting the floor
Claim: “A louder sound means more energy was created.” What’s wrong?
Energy was transferred, not created
A system transfers energy but does no useful work. Where did the energy likely go?
Into thermal energy
Two falling objects hit different surfaces. Why is the sound different?
Energy transforms differently based on surface properties
An object produces light without heat. Possible at this level? Explain.
No; light production usually involves thermal energy
A system produces motion without increasing heat noticeably. Which energy transfer must be minimized?
Friction (thermal energy transfer)
Claim: “If two objects move, they must have the same energy.” Disprove with one variable.
Mass or speed can differ, changing mechanical energy
How does reducing friction change the final energy distribution of a system?
More energy stays mechanical, less becomes thermal
Can two systems end with the same energy forms but start differently? Justify.
Yes; different sources can transform into the same outputs
Energy leaves a closed system but total energy stays the same. Is this a contradiction? Explain.
No; energy is conserved but transferred out