SAT Physics Subject Test

Chapter 15 Thermal Physics

In this chapter we will discuss heat and temperature, concepts that seem familiar from our everyday experience. The SAT Physics Subject Test expects you to know things about heat and temperature that go beyond what you see around you every day. In physics, heat is defined as thermal energy that’s transmitted from one body to another. While an object is capable of containing thermal energy (due to the random motion of its molecules), it doesn’t contain heat; heat is energy that’s in transitTemperature, on the other hand, is a measure of the concentration of an object’s internal thermal energy and is one of the basic SI units.


Temperature can be expressed in degrees Celsius (°C); water freezes at 0°C and boils at 100°C. Temperature can also be expressed in the absolute temperature scale, in which temperatures are expressed in kelvins (K). On the kelvin scale, water freezes at 273.15 K and boils at 373.15 K. (The degree sign is not used for absolute temperature.) The kelvin scale assigns a value of 0 K to the lowest theoretically possible temperature and a value of 273.16 K to the triple point of water (the temperature at which the three phases of water—liquid water, ice, and vapor—coexist).

Absolutely Metric

The SAT Physics Subject
Test doesn’t bother with
Fahrenheit. Know Celsius
and Kelvin.

A kelvin is equal in size to a Celsius degree, and the conversion between kelvins and degrees Celsius is approximately:

T (K) = T (°C) + 273

  1. Room temperature is 20°C. What’s this temperature in kelvins?

Here’s How to Crack It

To convert to kelvins, add 273: Room temperature is 20 + 273 = 293 K.