Kinetic energy is energy of motion. If an object has velocity, it has kinetic energy. An object's mass and velocity affect the amount of kinetic energy that an object has. The formula for kinetic energy is .5mv² where m is the mass in kilograms and v is the velocity in meters per second. The kinetic energy of an object is also equivalent to the amount of work that that something performed on it, excluding the force needed to overcome friction. Kinetic energy units are joules.

Examples: KE = .5mv2 KE = .5(100 kg)(5 m/s) KE = .5(2500 kg m2/s2) KE = 1250 kg m2/s2 or 1250 joules

• Begin by asking the students what kinds of energy exists. If they do not mention kinetic energy then ask them if an object that is moving has energy. Explain to them that this energy is motion energy, or kinetic energy.
• Tell the students that if an object has velocity, it has kinetic energy.
• Tell the students there are two things that affect the amount of kinetic energy of an object.
• Ask them what two things affect it. If they do not come up with mass, explain to them that if an object is heavier than another is, it has more energy in it if both have the same velocity. This is because it took more force to make it go that fast. If they do not come up with velocity, explain to them that if an object is moving faster it took more energy to make it move that fast so the object has more energy.
• Explain that if we know how fast an object is moving and its mass that we can determine how much kinetic energy it has.
• Now tell the students you have two demonstrations of kinetic energy for them.
• Take two objects with very different weights, i.e., a large textbook and a spiral notebook.
• Explain to the students that these two objects have different masses.
• Tell the students to listen to the sound that each of the objects makes when dropped from the same height.
• Raise the heavier object to some height and drop it.
• Then raise the lighter object to the same height and drop it.
• Ask the students if they thought the louder object had more or less kinetic energy.
• Explain to them that the sound they heard was the object losing its kinetic energy as it hit the ground, and that this loss of energy is greater and therefore louder in the heavier object.
• Now tell the students they can do their own demonstration with the model by doing the following:

1. Position one of the characters on an end of the lever.
2. Then hit the other end of the lever so the character flies off the lever.

• Explain that as they hit it the kinetic energy from their hands transfers across the lever and gives the character kinetic energy moving it off the lever.
• Explain that in the circus performers are moving so they have kinetic energy.
• Tell the students that the people in charge of the circus can calculate how high they need someone to jump to launch another performer up into the air.
mv² where m is mass in kilograms and v is velocity in meters per second.
• Now write on the board or overhead this sample problem:

• Tell the students to try to find the answer in the next few minutes.
• After a few minutes ask them what they think the answer is. When someone gets it right, write the following work on the board:

• Tell them that if they did not show units then their answer would be incorrect because units are necessary to determine type of unit of the answer.
• Explain that there are various ways to transfer kinetic energy. Two of these are direct contact and levers. The kinetic energy on one side of a lever is equal to the kinetic energy on the other side of the lever.
• Now handout the two worksheets on the following pages and let the students work on them in class and finish them up at home.

Kinetic energy leads up to:

• Potential Energy
• Friction

1. Kinetic energy is energy of _______________.

 

2. If an object has _________, it has kinetic energy.

 

3. ___________ and ___________ affect the amount of kinetic energy in an object.

 

4. The formula for kinetic energy is ____________.

 

5. __________ has more effect on kinetic energy than _____________.

 

6. ___________ need to be shown in a kinetic energy problem.

 

7. ________ _______ and ___________ are two ways to transfer kinetic energy.

 

8. The kinetic energy on one side of a lever is ________ to the kinetic energy on the other side.

 

9. A still object has __________ kinetic energy.

 

10. Write one example of how you use kinetic energy in your life.

1. Mr. Smith wants to find out how quickly he can propel an object off a lever if he drops his book on the other end. His book has a mass of 5 kilograms and hits the lever with a speed of 10 meters per second. The object he wishes to launch has a mass of 2 kilograms. What is the initial launch speed of the object?

2. Joe is playing baseball. He wants to know how fastel off a tee at 20 meters per second. The ball has a mass of .3 kilograms and the bat has a mass of 5 kilograms. How fast must the point of impact on his bat move if he wants the ball to move at 20 meters per second?

1. motion

 

2. velocity

 

3. mass; velocity

 

4. KE = .5mv²

 

5. velocity; mass

 

6. units

 

7. direct contact; levers

 

8. equal

 

9. no

 

10. answers will vary

1. Solution: 15.8 meters per second

2. Solution: 4.9 meters per second