# potential energy

## stored energy

The diver has energy because of her position high above the pool. The type of energy she has is called potential energy. Potential energy is energy that is stored in a person or object. Often, the person or object has potential energy because of its position or shape. Q: What is it about the divers position that gives her potential energy? A: Because the diver is high above the water, she has the potential to fall toward Earth because of gravity. This gives her potential energy.

## gravitational potential energy

Potential energy due to the position of an object above Earths surface is called gravitational potential energy. Like the diver on the diving board, anything that is raised up above Earths surface has the potential to fall because of gravity. You can see another example of people with gravitational potential energy in the Figure 1.1. Gravitational potential energy depends on an objects weight and its height above the ground. It can be calculated with the equation: Gravitational potential energy (GPE) = weight height Consider the little girl on the sled, pictured in the Figure 1.1. She weighs 140 Newtons, and the top of the hill is 4 meters higher than the bottom of the hill. As she sits at the top of the hill, the childs gravitational potential energy is: GPE = 140 N 4 m = 560 N m Notice that the answer is given in Newton meters (N m), which is the SI unit for energy. A Newton meter is the energy needed to move a weight of 1 Newton over a distance of 1 meter. A Newton meter is also called a joule (J). Q: The gymnast on the balance beam pictured in the Figure 1.1 weighs 360 Newtons. If the balance beam is 1.2 meters above the ground, what is the gymnasts gravitational potential energy? A: Her gravitational potential energy is: GPE = 360 N 1.2 m = 432 N m, or 432 J

## other forms of potential energy

All of the examples of potential energy described above involve movement or the potential to move. The form of energy that involves movement is called mechanical energy. Other forms of energy also involve potential energy, including chemical energy and nuclear energy. Chemical energy is stored in the bonds between the atoms of compounds. For example, food and batteries both contain chemical energy. Nuclear energy is stored in the nuclei of atoms because of the strong forces that hold the nucleus together. Nuclei of radioactive elements such as uranium are unstable, so they break apart and release the stored energy.

## elastic potential energy

Potential energy due to an objects shape is called elastic potential energy. This energy results when an elastic object is stretched or compressed. The farther the object is stretched or compressed, the greater its potential energy is. A point will be reached when the object cant be stretched or compressed any more. Then it will forcefully return to its original shape. Look at the pogo stick in the Figure 1.2. Its spring has elastic potential energy when it is pressed down by the boys weight. When it cant be compressed any more, it will spring back to its original shape. The energy it releases will push the pogo stickand the boyoff the ground. Q: The girl in the Figure 1.3 is giving the elastic band of her slingshot potential energy by stretching it. Shes holding a small stone against the stretched band. What will happen when she releases the band? A: The elastic band will spring back to its original shape. When that happens, watch out! Some of the bands elastic potential energy will be transferred to the stone, which will go flying through the air.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

a person or object may have stored energy because of its

``````a) shape.

b) position.

c) velocity.

-->  d) two of the above
``````

an objects potential energy due to gravity depends on its

``````a) weight.

b) acceleration.

c) height above the ground.

-->  d) two of the above
``````

a stretched rubber band has potential energy.

``````-->  a. true

b. false
``````

food and batteries both contain potential energy.

``````-->  a. true

b. false
``````

## diagram questions

No diagram questions associated with this lesson