Lesson: The First Law of Thermodynamics Physics • 9th Grade

In this lesson, we will learn how to calculate the change in the internal energy of a system by comparing the heating of and work done by the system.

Lesson Plan

Students will be able to

distinguish between the change of the internal energy of an object due to the heating or cooling of the object and the change of the internal energy of the object due to work done on or by the object,
use the equation in all combinations.

Lesson Worksheet

Q1:

A rope is pulled, increasing its tension. The work done pulling the rope is 23 J. While being pulled, the rope is also heated by the hand of the person pulling on it, by a net of 1.5 J. What is the change in the rope’s internal energy? Give your answer to one decimal place.

Q2:

A cylinder contains a gas that receives net heating of 15 J. While the gas is heated, the lid of the cylinder is moved upward through a distance of 15 cm, as shown in the diagram. The mass of the lid is 1.45 kg. How much does the internal energy of the gas increase during the heating? Give your answer to the nearest joule.

Q3:

A spring is compressed, increasing its tension. The work done compressing the spring is 1.32 J. While being compressed, the spring heats the hand of the person pushing on it by a net of 0.15 J. What is the change in the spring’s internal energy?