Heat & Thermal Energy
Temperature, heat flow, and thermal equilibrium
Do Now: You leave a hot cup of cocoa on the table. An hour later it’s at room temperature. Where did the energy go?
Into the air and the table around it. The energy was not destroyed — it spread out into the surroundings. This unit explains how and why.
Try It First
Put a hot object and a cold object in contact. Watch their temperatures.
Pick the materials, masses, and starting temperatures, then press “Touch them!”
Lessons
NYS P-12 Science Learning Standards, Physics: HS-PS3-4 — Plan and conduct an investigation to provide evidence that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components in the system (second law of thermodynamics).
Cooling a Laptop Processor
A laptop processor transforms electrical energy into thermal energy at a rate of 45 W. To prevent overheating, engineers attach an aluminum heat sink with many thin fins, and a small fan blows air across the fins.
Why does the heat sink have many thin fins instead of being a solid block?
▶ Want a challenge? Open 6 more Regents-style questions (harder · mixed formats)
Challenge score: 0 / 6
C1. In which direction does thermal energy flow?
C2. Suppose the fan fails and, for 30. s, all of the processor’s thermal energy goes into an 80.-g aluminum heat sink (c = 0.90 J/g·°C). Substitute numerical values into a mathematical representation that can be used to determine the temperature rise of the heat sink. Then calculate the temperature rise.
C3. A student makes the following claim.
Place a check mark in either the Support or Refute box. Justify your response.
C4. Place a check mark in three boxes to indicate changes that would increase the rate of heat transfer from the processor to the surrounding air.
C5. An engineer suggests making the heat sink from copper instead of aluminum. Copper conducts heat better but is heavier and more expensive. Which statement best evaluates this trade-off?
C6. Some thin laptops are “fanless”: they rely only on a heat sink and the laptop case. Identify one benefit and one drawback of a fanless design.