Energy

Energy

Mr. Hawboldt

Open Ended

What is the definition of energy?

Energy

• "is the capacity to do work"

• measured in Joules (J) (pronounced like jewels)

• comes in many different forms/types

• CANNOT be negative

Open Ended

Give an example of a type of energy

Energy

• For this unit, we will focus on 2 types of energy (with an honorable mention for a third type)

• The two types we will look at are kinetic energy and gravitational potential energy

Open Ended

Use a single word to describe the word "kinetic"

Kinetic Energy

• is the energy of motion

• anything that is moving (has a velocity) has kinetic energy

• is represented by the letter K (sometimes  $KE$   or  $E_K$  )

•  $K\ =\ \frac{1}{2}mv^2$  

• measured in Joules (J)

Multiple Choice

A 10 kg cat runs across the room with a speed of 5 m/s. How much kinetic energy does the cat have?

• 50 Joules

• 2 Joules

• 250 Joules

• 125 Joules

Multiple Choice

Which of the following has more kinetic energy?

• A 1000 kg car moving at 10 m/s

• A 4000 kg semi truck moving at 5 m/s

• They have the same kinetic energy

Open Ended

What is the definition of "potential"?

Potential Energy

• is energy stored in an object (it COULD do work)

• measured in Joules (J)

• can come from many different kinds of energy

• Examples: stored electricity, stored chemical energy in batteries, etc

•  represented by  $U$  
  

GRAVITATIONAL potential energy

• energy stored in an object due to its distance from the Earth

• lifting an object gives it the POTENTIAL to fall back down

• represented by  $U_g$  

• measured in Joules (J)

•  $U_{g_{ }}=mgh$  

• m = mass; g = 9.8; h = height off the ground

Multiple Choice

A 2 kg book is sitting on a shelf 5 meters from the ground. How much gravitational potential energy does the book have? (To make things easier for now, use g = 10 m/s²)

• 2 Joules

• 10 Joules

• 50 Joules

• 100 Joules

Multiple Choice

Which has more gravitational potential energy?

• A 0.25 kg apple sitting on a countertop 1 meters off the ground

• A 1000 kg car sitting the driveway on the ground.

• They have the same gravitational potential energy

Summary

•  $K=\frac{1}{2}mv^2$                        $U_g=mgh$  

• kinetic energy is associated with movement (velocity)

• gravitational potential energy is associated with position (height)

• All energy is measured in Joules (J)

• energy CANNOT be negative

• change is energy CAN be negative