Light is energy that travels in rays. Some of these rays we can see, so we call that visible light. Some of the rays we cannot see but we can feel their effect on us. We cannot see ultraviolet (UV) rays but they burn our skin when we are in the Sun without sunblock. We can also not see infrared rays but we can feel how hot they are on our skin.

Your body also needs sunlight to make Vitamin D in your skin. Without Vitamin D your body cannot absorb calcium and your bones cannot grow and get strong.

Light comes from a light source. Anything that produces light is called a source of light.

• The Sun is a source of light.
• Stars are sources of light.
• A fire is a source of light.
• A candle is a source of light.
• An electric bulb is a source of light.

Do you enjoy standing outside on a warm summer day and feeling the warmth from the Sun on your skin? What about warming your hands on a frosty cold morning in front of a fire? You are feeling heat! We discussed that the Sun provides us with light, but it also provides us with heat.

Heat can be found in many different places. Anything that provides us with heat is a source of heat. Let's look more closely at different sources of heat energy.

When objects are moving, they have movement. The faster the object is moving, the more movement it has. Look at the examples of movement below.

Did you know sound is also a type of energy?! Sound is everywhere.

Sound is a special type of movement. Sound is energy that makes substances vibrate. Sound travels as vibrations that we can hear and sometimes even feel. All sounds are caused by vibration of substances.

Sound can come from different sources. You can clap your hands, stamp your feet, talk, sing or play a musical instrument. Different vibrations will make different sounds.

Energy is also stored in some sources. Stored energy is the energy that is stored in our food, in petrol, in wood, oil and other chemicals. Batteries also contain chemicals which are used to store energy. This stored energy can be used for different purposes.

Examples:

1. When we eat food, the stored energy in the food can be used by our bodies.
2. When we burn wood or coal, the stored energy is released as heat energy that we can use to keep us warm.
3. When we burn gas, we can use it to cook our food.
4. When we turn on a car, we use the energy in the petrol to give movement energy to the car.

Energy can also be transferred (moved) from one part of a system to another part.

You must have heard of electricity before? We use electricity every day in our modern lives. Electrical energy can be transferred from a source to an appliance or light bulb.

Look at this picture of the light bulb below. Electrical energy is transferred from a source to the light bulb to make it glow.

Have you ever used a torch before? How do you think the bulb lights up in the torch? The batteries are the source of energy in the torch. When the torch is turned on, the energy is transferred from the batteries to the bulb to make it light up so you can see in the dark.

This brings us to the next section. We can think of the energy in the batteries of the torch as being the input energy and the light energy that is given off by the bulb as the output energy.

We use lots of appliances in our lives. These machines and appliances need input energy to make them work. This is usually electrical energy. The output energy (the work the appliance or machine does) is something that is useful to us.

Let's look at some examples.

In summary, we can say that in appliances and machines, the input is normally electrical energy and the output depends on the appliance:

• Heat energy - from a geyser, stove, kettle, hair dryer
• Sound energy - from a drill, vacuum cleaner, hair dryer
• Light energy - from a lamp, torch
• Movement - from an electric fan, drill