Module 6—Work and Energy
Lesson Summary
In this lesson you explored the following questions:
- How do you know how much work is done by a chairlift?
- What effect do conservative and non-conservative forces have on the gain in mechanical energy of the skiers on the lift?
- What is the work-potential energy theorem?
In the presence of a conservative force (gravity), the work done in raising an object, such as a skier, through a vertical distance is equal to the gain in potential energy of that object. This is known as the work-potential energy theorem.
In the presence of both a non-conservative force (friction) and a conservative force (gravity), the work done raising an object vertically is equal to the sum of the gain in potential energy and the work done to overcome the non-conservative force. For example, the work done by a chairlift is not equal to the gain in mechanical energy of the riders since some energy is lost working against the force of friction. The longer the pathway, the more energy that is lost to the non-conservative force.
Lesson Glossary
work-energy theorem: a statement that says the work done on a closed system is equal to the sum of the changes in the potential and kinetic energies of the system
work-potential energy theorem: a statement that says the work done in a gravitational field is equal to the change in potential energy