Vocabulary
Define thermal energy.
Thermal energy is the total kinetic and potential energy of all the particles in a substance.
What does temperature measure about the particles in a substance?
Temperature measures the average kinetic energy of the particles.
Name the three ways thermal energy transfers.
Conduction, convection, and radiation
List three factors that affect how much thermal energy is needed to change an object's temperature.
Type of matter (material), state of matter (solid/liquid/gas), and amount of matter (mass)
What does it mean to "optimize" a design solution in engineering?
To optimize means to test and revise a design so it best meets the project's needs, balancing performance, cost, weight, and other constraints.
What is "specific heat"? Give the units used.
Specific heat is the amount of thermal energy required to raise the temperature of 1 kilogram of a material by 1 kelvin; units: Joules per kilogram Kelvin (J/kg·K).
Why does a bathtub of warm water have more thermal energy than a cup of hot coffee, even if the coffee is hotter?
The bathtub has many more particles, so the total kinetic energy (thermal energy) is larger even though the average kinetic energy per particle (temperature) is lower.
Give two everyday examples of conduction.
Possible answers:
A metal spoon getting hot in soup (energy moves from the soup to the spoon by direct contact).
Ice melts in your hand (energy moves from your hand to the ice by direct contact).
When two objects of equal mass receive the same amount of thermal energy, the one with the lower value of _________ will experience a greater temperature change.
specific heat
Name two design choices you would make to keep a cooler cold for hours.
Use a hard outer plastic shell (poor conductor) and inner foam insulation that traps air; include a tight-sealing lid to reduce convection.
Explain what "thermal conductivity" measures.
Thermal conductivity measures how well a material transfers thermal energy (units: W/m·K).
Name the three temperature scales, and give one boiling or freezing point for each.
Celsius: water freezes at 0°C and boils at 100°C.
Fahrenheit: water freezes at 32°F and boils at 212°F.
Kelvin: water freezes at 273 K and boils at 373 K.
Describe how convection currents form in a fluid.
Warmer fluid becomes less dense and rises, while cooler, denser fluid sinks; this rising and sinking creates circulation called convection currents.
Explain why liquids usually require more energy to change temperature than solids.
In solids, particles only vibrate in place. When you add thermal energy, all that energy goes into making them vibrate faster, which raises the temperature.
But in liquids, particles can move around and slide past each other. When you add thermal energy to a liquid, some energy also gets used up helping particles break free from their neighbors so they can move around and some energy goes into making particles move faster (which raises temperature). Since the energy has to do two jobs instead of one, you need more energy to heat up a liquid the same amount as a solid.
Think of it like this: heating a solid is like making people dance in their seats, but heating a liquid is like making people get up, move around the room, AND dance at the same time!
Explain why aluminum is commonly used for car radiators.
Aluminum has high thermal conductivity so it transfers heat away from the engine efficiently; it is also relatively lightweight and cost-effective.
What is the difference between a conductor and an insulator? Give an example of each.
A conductor allows thermal energy to flow easily (for example, metals); an insulator slows the flow of thermal energy (for example, wool or fiberglass).
Explain how adding thermal energy can change the state of matter.
Adding thermal energy increases particle motion. If enough energy is added, particles can overcome bonds between them, causing a solid to melt into a liquid or a liquid to become a gas.
Explain why radiation can transfer thermal energy through empty space and give two everyday examples.
Radiation is energy carried by electromagnetic waves and does not need matter to travel, so it can move through a vacuum; examples: the Sun warming Earth, the coils in a toaster warming bread, warming your hands next to a campfire
Compare specific heats:
ice (2,108 J/kg·K),
liquid water (4,182 J/kg·K),
water vapor (1,996 J/kg·K)
Which requires the most energy to raise temperature and why?
Liquid water requires the most energy to raise temperature because it has a higher specific heat.
Describe one safety application where insulators are crucial (very important) and which insulator property is most important.
Protective gear for steel-mill workers and firefighters uses insulators to minimize heat transfer; the most important property is very low thermal conductivity combined with the ability to withstand high temperatures.
What is a definition of "heat" that clarifies the everyday use of the word vs. the scientific meaning of the word.
Heat (scientific) is the flow of thermal energy from a warmer object to a cooler object; everyday people often call something "hot" but scientists use "heat" only for energy transfer.
Scuba tank A has air at the same temperature as tank B, but twice the number of particles.
How does the thermal energy and temperature compare between A and B?
Tank A has twice the thermal energy because it has twice as many particles at the same average kinetic energy (temperature); the temperature is the same in both tanks.
A metal pan sits on a hot stovetop burner.
Describe step-by-step how conduction moves thermal energy from the burner to the pan, then to the handle of the pan, and why the handle might still stay cooler for a while.
The burner heats the bottom of the pan, causing the metal molecules to vibrate faster. These vibrating molecules bump into nearby molecules, passing energy along like a chain reaction that spreads upward through the pan and outward toward the handle.
The handle stays cooler longer because it's farthest from the heat source, so it takes more time for the energy to travel there. Also, the handle loses some heat to the air around it, which helps keep it cooler.
Eventually, if left on the burner long enough, even the handle will become too hot to touch as the heat continues to spread throughout the entire pan.
A 1 kg sample of aluminum (≈897 J/kg·K) and a 1 kg sample of maple wood (≈1,600 J/kg·K) each receive the same amount of thermal energy.
Which one will show a larger temperature increase? Explain.
A 1 kg sample of aluminum will show a larger temperature increase than a 1 kg sample of maple wood because it has the lower specific heat, so it needs less energy per kilogram to raise its temperature by 1 K.
Design a simple ice chest (cooler) to keep ice cream frozen longer during a summer picnic.
List three material choices or design elements.
1) Thick foam walls to block heat conduction from outside air.
2) Reflective aluminum lining to bounce heat radiation away from the contents.
3) Tight-fitting lid with rubber seal to prevent warm air from getting in through convection.