Activity 3.1: Work of Constant and Non-Constant Forces
How is work and power measured for lifting an object with constant and non-constant forces?
Few forces in nature are constant. A good example of a non-constant force is the force exerted by a spring as you stretch it. In this investigation you will see how to calculate work and power when a non-constant force acts on an object.
AP® Learning Objectives:
Materials Required include, but are not limited to:
Work of a Constant Lifting Force
Work of a Non-Constant Lifting Force
In this activity you will measure the work done when you stretch a spring through a measured distance. First you will collect data for force applied by a stretched spring vs. distance the spring is stretched, and you will plot a graph of force vs. distance. Then, as in the previous activity, you will be able to calculate the work done by finding the area under this graph.
Kinetic Energy and the Work-Energy Principl
What happens when you apply an external force to an object that is free to move and has no frictional forces on it? According to Newton’s second law, it should experience an acceleration and end up moving with a different velocity. Can we relate the change in velocity of the object to the amount of work that is done on it?
When an object moves, it possesses kinetic energy because of the work that was done to start it moving.
The amount of kinetic energy increases with both mass and speed.
When you apply a net force to an object, the object always accelerates. The force does work and the kinetic energy of the object changes. The relationship between the work done on the object and the change in its kinetic energy is called the work-energy principle.
In short, the work-energy principle states that the net work (considering all forces acting on the object) is equal to the change in the object‘s kinetic energy.
In this activity, you will examine the work-energy principle by doing work on a cart with a spring and comparing this work to the change in the cart‘s kinetic energy.