Unit 4 Lesson 3: Energy and its Forms

Energy and Work

●In order to define energy, you need to return to the definition
of a related topic, work. Recall that work is done when a force moves an
object through a distance. Energy is the ability to do work.

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In other words, energy is transferred by a force moving an object through a

distance.

●Work and energy are closely related. When work is done on an object, energy
is transferred to that object. Work is a transfer of energy. Both work and
energy are typically measured in joules (J).

​don't tell on yourself

Energy can be divided into two types: Potential and Kinetic​

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​Types of Energy

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​You DO NOT need to copy down the entire chart. Just list the examples of kinetic and potential energy.

Kinetic Energy

●The energy of motion is called kinetic energy.

​Notice that velocity is squared! Speed has a much bigger impact on your kinetic energy than mass does!

Multiple Choice

If your velocity tripled, how much bigger would your kinetic energy get?

• 3x the energy

• 4.5x the energy

• 6x the energy

• 9x the energy

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​DON'T ERASE YOUR BOARD UNTIL INSTRUCTED!

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​If your group gets the right answer, hold up your board!

You're going to use this to show your work.​ Take note of the measurements given in the problem and use them to find the solution!

​Grab a whiteboard and marker!

​Let's try it!

Fill in the Blank

A 0.1 kg bird is flying at 8 m/s. What is the bird's kinetic energy? Include units in your answer!

Fill in the Blank

A 1400 kg car moves at 25 m/s. What is the car's kinetic energy? Include units in your answer!

Potential Energy

●Potential Energy is energy that is stored as a result of position or shape.

●Two forms of potential energy are

1. gravitational potential energy

2. elastic potential energy

Gravitational Potential Energy

●When you lift your bag up to leave class at the end of the block, you do work
to increase the potential energy of your bag.

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Potential energy that depends upon an object’s height is called

gravitational potential energy. This type of potential energy increases when

an object is raised to a greater height.

Fill in the Blank

Suppose a diver at the top of a 10.0 m high diving platform has a mass of 50.0 kilograms. What is their gravitational potential energy? (Include units of measurement!)

Gravitational Potential Energy Cont.

●Suppose a diver at the top of a 10.0 m high diving platform has a mass of
50.0 kilograms. You can calculate their potential energy relative to the ground
as follows.

○PE = mgh

○PE = (50.0 kg)(10 m/s^2)(10.0 m)

○PE = 5000 kg x m^2/s^2 = 5000 J

Elastic Potential Energy

●The potential energy of an object that is stretched or compressed is known as
elastic potential energy. Something is said to be elastic if it springs back to
its original shape after it is stretched or compressed. Think of a rubber band
that you stretch and then it comes back to its original shape.

●Elastic potential energy can also be stored in objects that are compressed,
such as springs. Drop a slice of bread on the floor and it does not bounce
noticeably. The bread is not very elastic.

●Drop a basketball on the floor and the basketball bounces back up. The
compressed air in the ball forces the ball to spring back into shape after hitting
the ground, propelling the ball back up.

Mechanical Energy

●The energy associated with the motion and position of everyday object is
mechanical energy. Mechanical energy is not just limited to machines.
Mechanical energy is the sum of an object’s potential energy and kinetic
energy. Speeding trains, bouncing balls, and sprinting athletes all have
mechanical energy.

Energy Conversion

●Energy can be converted from one form to another. The process of changing
energy from one form to another is energy conversion.

Conservation of Energy

●When energy changes from one form to another, the total energy remains
unchanged even though many energy conversions may occur. This is one of
the most important concepts in science: the law of conservation of energy.
The law of conservation of energy states that energy cannot be created or
destroyed.

Energy Conversions

●One of the most common energy conversions is between potential energy
and kinetic energy. The gravitational potential energy of an object is converted
to the kinetic energy of motion as the object falls.

●Conversions between kinetic and potential energy can happen in both
directions, that is, from kinetic to potential energy, or from potential to kinetic
energy.

Match

Match the following vocab terms!

• Energy

• Gravitational Potential Energy

• Kinetic Energy

• Energy Conversion

• Elastic Potential Energy

the ability to do work

Potential Energy that depends upon an object's height

the energy of motion

The process of changing energy from one form to another

potential energy of an object that is stretched or compressed

• the ability to do work

• Potential Energy that depends upon an object's height

• the energy of motion

• The process of changing energy from one form to another

• potential energy of an object that is stretched or compressed

Conservation of Energy Cont.

●According to the law of conservation of energy, energy can be converted from
one form to another. However, in a closed system, the amount of energy
present at the beginning of a process is the same as the amount of energy at
the end. (In a closed system, nothing can enter or leave.)

Open Ended

You know that if you stop pedaling when you’re riding a bike on a flat path, the bike will eventually come to a stop. Where did the kinetic energy go from the moving bike?

Conservation of Energy Cont.

●According to the law of conservation of energy, energy can be converted from
one form to another. However, in a closed system, the amount of energy
present at the beginning of a process is the same as the amount of energy at
the end. (In a closed system, nothing can enter or leave.)

​The bike slowed down due to friction forces and the energy was converted into thermal energy. Your bike is not part of a closed system because friction was doing work to slow you down!​