Potential energy is energy stored in an object. This energy has the potential to do work. Gravity gives potential energy to an object. This potential energy is a result of gravity pulling downwards. The gravitational constant, g, is the acceleration of an object due to gravity. This acceleration is about 9.8 meters per second on earth. The formula for potential energy due to gravity is PE = mgh. As the object gets closer to the ground, its potential energy decreases while its kinetic energy increases. The difference in potential energy is equal to the difference in kinetic energy. After one second, if the potential energy of an object fell ten units than its kinetic energy has risen ten units. Potential energy units are joules.

Formula:

W = Fd kg m/s² meters Work equals force times distance,

F = ma kg m/s² Force equals mass times acceleration,

a = g m/s² Acceleration is g,

F = mg kg m/s² So force equals mass times g,

W = mgd kg m/s² meters Which means work equals mass times g times distance,

d = h meters Distance equals height,

W = mgh kg m/s² meters Which makes work equal to mass times g times height,

W=PE Which means potential energy it the amount of work an object could do.

Example: PE = mgh PE = (20 kg)(9.8 m/s2)(10 m) PE = (20 kg)(98 m2/s2) PE = 1960 kg m2/s2 or 1960 joules This block can perform 1960 joules of work.

• Take out a rubber band.
• Stretch out the rubber band.
• Ask the students if it has any energy.
• Release rubber band.
• Explain to the students that it did have energy, potential energy. This energy became kinetic energy as the rubber band was released.
• Explain that potential energy is the stored energy in an object and that it has the potential to become kinetic energy.
• Tell the students gravity causes objects above the ground to have potential energy. If the object stays in the air, it has the potential to fall.
• Explain to the students that there are three things required to calculate how much potential energy gravity causes an object to have.
• Tell them that the first is how high the object is off the ground, the second is the mass of the object, and the last is the amount of gravitational acceleration.
• Tell the students that potential energy is equal to mgh. In this equation, m is mass in kilograms, g is acceleration due to gravity in meters per second squared, and h is the height of the object.
• Explain that gravitational acceleration is a constant, on earth it is 9.80655 meters per second.
• Pick up some object that you can drop.
• Raise it in the air.
• Tell the students that the object now has potential energy because of gravity.
• Drop the object.
• Explain to the srted into kinetic energy.
• Now have the students use their model to do the following demonstration:

1. Put two characters on the platform of the model and one on the far end of the lever.
2. Slide the two characters down their wire onto the end of the lever.
3. Now lift the other character off having him follow the copper wire path.

• Explain that the two characters had potential energy while on top of the platform and as they jumped it turned into kinetic energy. This kinetic energy transferred to the other side lifting the other performer into the air.
• Tell the students that the performers have potential energy whenever they are in a position where they will fall.
• Explain that potential energy is used to calculate how high a performer will be launched off a lever.
• Tell them that the change in potential energy is equal to the opposite of the change in kinetic energy. For example, if a ball lost ten units of potential energy it gained ten units of kinetic energy.
• Explain that if the potential energy falls to zero then the kinetic energy rises to whatever the potential energy was before.
• Tell the students that potential energy problems also need to have units shown.
• Write the following problem on the board or overhead:

• Give the students a few minutes to solve the problem.
• Then write the following solution on the board:

• Have the students work on the two worksheets on potential energy and finish them for homework.

Potential energy leads up to:

• Potential Energy in springs - a different formula with different applications

1. Potential energy is __________ energy.

 

2. __________ is one thing that causes potential energy.

 

3. An object has potential energy if it has ___________.

 

4. ________, ________, and __________ affect the amount of potential energy in an object.

 

5. The formula for potential energy is ____________.

 

6. __________ must be shown with potential energy problems.

 

7. The change in potential energy is _________ to the opposite of the change in kinetic energy.

 

8. Gravitational acceleration is a ___________.

 

9. An object potential energy at the __________ of a fall equals an objects kinetic energy at the __________ of a fall.

 

10. Write down one real world example of potential energy.

1. John has an object suspended in the air. It has a mass of 50 kilograms and is 50 meters above the ground. How much work would the object do if it was dropped?

 

 

 

 

 

 

 

 

 

 

 

2. Mrs. Jacobs dropped an object from 10 meters. She knows it did 50 joules of work. How much did it weigh?

1. stored

 

2. gravity

 

3. height

 

4. mass; gravity; height

 

5. PE = mgh

 

6. units

 

7. equal

 

8. constant

 

9. start; end

 

10. answers will vary

1. Solution: 24516.375 joules

2. Solution: .5 kilograms