2.08 &2.09 Kinetic and Potential Energy

• Kinetic and Potential Energy
• 6th Grade

SCI06A~Johnson

2.08 & 2.09

Kinetic and Potential Energy

Objective

We will identify and explain the difference between kinetic and potential energy.

Agenda

• What is energy?
  
• What are the two types of energy?
• What makes them different?
  

energy

You have 2 minutes to update a vocabulary card for energy.

kinetic energy

the energy of an object or substance because of its motion

potential energy

energy stored in an object based on its position.

What two variables influence kinetic energy?

Kinetic Energy Formula

kinetic energy

Here are the steps to solve for kinetic energy

1. Plug your information into the formula
2. Square the quantity for speed.
3. Find one half of the mass.
4. Multiply these two numbers together.
5. Write the resulting answer in joules (J).

Calculating Kinetic Energy

A marble has a mass of 0.05 kg. You shoot it out of your hand and send it moving at a speed of 2 m/s. How much kinetic energy does the marble have?

1. Plug your information into the formula.
2. Square the quantity for speed.
3. Find one half of the mass.
4. Multiply these two numbers together.
5. Write the resulting answer in joules (J).

ke=​2​​1​​mv​2​​

ke=​2​​1​​0.05kg(2​s​​m​​)​2​​

Calculating Kinetic Energy

A marble has a mass of 0.05 kg. You shoot it out of your hand and send it moving at a speed of 2 m/s. How much kinetic energy does the marble have?

1. Plug your information into the formula.
2. Square the quantity for speed.
3. Find one half of the mass.
4. Multiply these two numbers together.
5. Write the resulting answer in joules (J).

ke=​2​​1​​mv​2​​

ke=​2​​1​​0.05kg(2​s​​m​​)​2​​

ke=​2​​1​​0.05kg⋅4​s​2​​​​m​2​​​​

Calculating Kinetic Energy

A marble has a mass of 0.05 kg. You shoot it out of your hand and send it moving at a speed of 2 m/s. How much kinetic energy does the marble have?

1. Plug your information into the formula.
2. Square the quantity for speed.
3. Find one half of the mass.
4. Multiply these two numbers together.
5. Write the resulting answer in joules (J).

ke=​2​​1​​mv​2​​

ke=​2​​1​​0.05kg(2​s​​m​​)​2​​

ke=​2​​1​​0.05kg⋅4​s​2​​​​m​2​​​​

ke=0.025kg⋅4​s​2​​​​m​2​​​​

Calculating Kinetic Energy

A marble has a mass of 0.05 kg. You shoot it out of your hand and send it moving at a speed of 2 m/s. How much kinetic energy does the marble have?

1. Plug your information into the formula.
2. Square the quantity for speed.
3. Find one half of the mass.
4. Multiply these two numbers together.
5. Write the resulting answer in joules (J).

ke=​2​​1​​mv​2​​

ke=​2​​1​​0.05kg(2​s​​m​​)​2​​

ke=​2​​1​​0.05kg⋅4​s​2​​​​m​2​​​​

ke=0.025kg⋅4​s​2​​​​m​2​​​​

ke=0.1J

A 50-kg girl is playing soccer. She runs toward the ball at a speed of 7 m/s. How much kinetic energy does she have as she runs? Calculate the answer to this problem using the equation KE = ½mv2.

 A 50-kg girl is playing soccer. She runs toward the ball at a speed of 7 m/s. How much kinetic energy does she have as she runs? Calculate the answer to this problem using the equation KE = ½mv2.

[4] KE = ½ (50 kg) (7 m/s)2

     KE = (25 kg) (49 m/s)

     KE = 1,225 J

The girl has 1,225 J of kinetic energy as she runs toward the soccer ball.

Why Is Kinetic Energy Important?

Work changes the energy of an object. So if an object, such as a truck, has a lot of kinetic energy, it takes a lot of work to stop it. Imagine that there are two trucks that are the same mass (2,000 kg) and have the same braking force. Truck A is traveling 20 m/s, and Truck B is traveling 40 m/s. How do you think their kinetic energies will compare?

Work changes the energy of an object. So if an object, such as a truck, has a lot of kinetic energy, it takes a lot of work to stop it. Imagine that there are two trucks that are the same mass (2,000 kg) and have the same braking force. Truck A is traveling 20 m/s, and Truck B is traveling 40 m/s. How do you think their kinetic energies will compare?

Potential Energy

Gravitational Potential Energy Equation

A 2 kg bowling ball sits on top of a building that is 40 m tall. What is the KE?

elastic potential energy

energy stored due to a change in shape in a material that tends to return to its original shape

elastic potential energy

energy stored due to a change in shape in a material that tends to return to its original shape

Example

 Opening the trap winds the coil of the mousetrap’s spring tighter. The spring has to be held in place in this unnatural shape by a small metal bar. At this point, the spring has elastic potential energy. When the trap snaps shut, the spring loses elastic potential energy as it returns to its normal shape.

What is another object that stores
elastic potential energy?

Potential Energy Equation

A 2 kg bowling ball sits on top of a building that is 40 m tall. What is the PE?

gravitational potential energy

energy invested in a body by lifting it against the force of gravity

gravitational potential energy

energy invested in a body by lifting it against the force of gravity

Gravitational Potential Energy

This skateboarder entering the half-pipe also has gravitational potential energy. As soon as she shifts her body, gravity will act on her, and she will travel down toward the base of the half-pipe.

What is another object that stores
gravitational potential energy?

Gravitational Potential Energy Equation

The formula for weight that you used in previous lessons is (w = mg), or weight = mass (kg) x acceleration due to gravity (m/s2). By substituting mg for w in the original formula

A 2 kg bowling ball sits on top of a building that is 40 m tall. What is the GPE?

A 2-kg bowling ball is 2.5 meters off the ground on a post when it falls. Just before it reaches the ground, it is traveling 7 m/s.

What is the ke?

A 2-kg bowling ball is 2.5 meters off the ground on a post when it falls. Just before it reaches the ground, it is traveling 7 m/s.

What is the gpe?

Explain the difference between kinetic energy and potential energy.

How does elastic potential energy differ from gravitational potential energy?

Determine the gravitational potential energy of a 7.5-N object ready to fall from a height of 5 m. Show your work.