Phys Sci 9.1

What is Energy?

​Chapter 9
Lesson 1

In science, energy is the ability to do work. Work is done when a force causes an object to move in the direction of the applied force.

How do energy and work help you play tennis?

When a tennis player swings their racket, they apply a force to the racket. This causes the racket to do work on the tennis ball. The racket transfers energy to the ball, making it fly through the air.

Energy is the reason the racket can do work on the ball. Work is the transfer of energy from one object to another. Both work and energy are measured in the unit of joules (J).

Multiple Choice

Work is the transfer of ________

• vibrations

• energy

• joules

• kinetic

When the tennis player hits the ball with the racket, energy is transferred from the racket to the tennis ball. The tennis ball now has kinetic energy, which is the energy of motion. All moving objects possess kinetic energy, and this energy can be used to do work, just like the kinetic energy of a hammer doing work on a nail.

To make this concept more simple:

• Kinetic energy is the energy of motion - all things that are moving have this type of energy.

• Just like a hammer can use its kinetic energy to drive a nail into wood, the tennis ball's kinetic energy can be used to do work.

What is Kinetic Energy?

Calculating Kinetic Energy

​The m is the object’s mass in kilograms.

The v is the object’s speed. This is also doubled which is why there is a power of 2 above the v.

The kinetic energy of an object is large if: • the object has a large mass, or • the object is moving fast

Kinetic Energy is always labeled
in Joules (J).

Multiple Choice

Kinetic energy is ______

• the movement of bodies

• the movement of objects

• the movement of al things

• the movement of energy

Gravitational Potential Energy

When you lift an object, you are doing work on it. This means you are moving the object in a direction that is opposite to the force of gravity. As you lift the object, you are transferring energy to it, giving it gravitational potential energy.

The amount of gravitational potential energy an object has depends on two things:

1. The object's weight: Heavier objects have more gravitational potential energy than lighter objects.

2. The object's distance from the ground: The higher you lift an object, the more gravitational potential energy it has.

Multiple Select

What two things does gravitational energy depend on?

• objects weight

• objects distance from ground

• objects length

• objects distance from the ceiling

Calculating Gravitational Potential Energy

​The gravitational potential energy of an object can be determined by using the following equation:


gravitational potential energy= weight x height


The weight is in newtons (N) and the height is in meters (m). Gravitational potential energy is written in newton x meters (N x m). Gravitational Potential energy is always measured in Joules (J).

Multiple Choice

To calculate gravitational energy you need to multiply the..

• weight and distance

• length and height

• length and width

• weight and height

Mechanical Energy

Mechanical energy is the total energy of motion and position of an object.

In other words, it is the kinetic energy plus the potential energy of an object.



All the energy in the juggler’s pins is in the form of mechanical energy

Multiple Choice

Mechanical energy is the kinetic energy plus _____ energy

• potential

• sound

• nuclear

• light

Thermal Energy

Matter is made of particles that are moving. These particles have kinetic energy. Thermal energy is all the kinetic energy from the movement of the particles in an object.

Particles move faster at higher temperatures than at lower temperatures. The faster the particles move, the greater their kinetic energy and thermal energy are.

Electrical Energy

You use electrical energy every day. Electrical outlets in your home allow you to use this energy. Electrical energy is the energy of moving particles called electrons. Electrons are the negatively charged particles of atoms.

Electrical energy has both kinetic energy and potential energy. When electrical energy runs through a wire, it uses its kinetic energy. Electrical energy that is waiting to be used is potential energy. This potential energy is in the wire before you plug in an electrical appliance.

Multiple Choice

Electrical energy is the energy of moving particles called neutrons

• True

• False

Sound Energy

Sound energy is the energy from a vibrating object. Vibrations are small movements of particles of an object.

In the figure , the guitar player pulls on the guitar string. This gives the string potential energy.

When they let go of the string, the potential energy turns into kinetic energy. This makes the string vibrate.

When the guitar string vibrates, some of its kinetic energy moves to nearby air particles. These vibrating air particles cause sound energy to travel so that it can be heard.

Light Energy

Light is a form of energy that helps us see the world around us. However, not all light can be seen by the human eye.

Here's a simple explanation of light and its properties:

-Light is made up of vibrations of electrically charged particles.
-These vibrations create light energy, similar to how sound energy is created by the vibration of particles.



However, unlike sound energy, light energy can travel through a vacuum, which is an area with no matter.

We use light in many ways, even if we can't see it. For example, microwaves are a type of light energy that we use to cook food, but we can't see them with our eyes.

Multiple Choice

All light can be seen by the human eye

• True

• False

Nuclear Energy

Another type of energy is stored in the nucleus of an atom. This energy is called nuclear energy, and it is stored as potential energy.

There are two ways that nuclear energy can be released from a nucleus:

1. Fusion: When two or more small nuclei join together, they release energy in a reaction called fusion. The sun's light and heat come from fusion reactions.

2. Fission: When a large nucleus, like uranium, is split apart, it releases energy in a process known as fission. Fission is used to create electrical energy at nuclear power plants.

Multiple Select

Nuclear energy is released in these two ways.

• vibrations

• fusion

• energy

• fission