Light & Sound for Year 3 & 4, Key Stage 2 Science for kids

Why we need light

We need light to see the world around us. Without light, everything would be dark because darkness is the absence of light.

We can see objects because light:

comes directly from a light source, or
reflects off objects and travels into our eyes

Light sources give out their own light. Examples include:

the Sun
stars
flames (like candles or fires)
light bulbs and lamps

When light hits an object, it bounces off the surface and enters our eyes. This helps us see the object’s shape, colour, and position.

Sun safety - important warning!

The Sun is a very powerful light source. Its light can seriously damage your eyes.

NEVER look directly at the Sun.
Even wearing sunglasses does not make it safe to stare at the Sun.

Looking directly at the Sun can:

burn the inside of your eyes

cause permanent eye damage

lead to blindness

This is a real scientific fact, not just a warning from adults. Always protect your eyes by looking away from the Sun and using shade when it is very bright.

The Sun is so bright that its light takes only about 8 minutes to travel all the way from the Sun to Earth.

Reflecting light

Most objects around us do not make their own light. Instead, we see them because light from a light source hits the object and then reflects (bounces) into our eyes.

For example, a desk, cup, or pen does not glow. These objects are visible because they reflect light from the Sun or a lamp.

Some materials reflect light better than others:

Mirrors reflect almost all the light that shines on them
Shiny surfaces reflect more light than dull ones
Dark or rough surfaces absorb more light and reflect less

This is why mirrors look bright and shiny, while dark tables or carpets look much duller.

A mirror reflects light so well because it has a very smooth surface, allowing light to bounce straight back instead of scattering in lots of directions.

Shadows

Light travels in straight lines and cannot bend around objects. When a solid object blocks the light, it creates a shadow.

A shadow is a dark area where light cannot reach.

Shadows:

appear on the opposite side of the light source
have the same shape as the object making them
are formed when light is blocked by a solid object

Changing shadow size

The size of a shadow depends on how close the object is to the light source:

When the object is close to the light source, the shadow is large
When the object is far away, the shadow is smaller

The position of the light source also affects where the shadow appears.

Make your own shadow

Turn on the torch or lamp.
Hold your hand in front of the light to make a shadow.
Move your hand closer to the light.
Move your hand further away.
What do you notice? How does the shadow change size? Does the shape of the shadow change?

How sounds are made

Sound is made when something vibrates. A vibration is a quick back-and-forth movement.

When an object vibrates, it makes the air around it vibrate too. These vibrations travel through the air as sound waves. When the sound waves reach your ear, they make your eardrum vibrate, and your brain understands this as sound.

Examples of vibrating objects:

Guitar strings vibrate when they are plucked
Drum skins vibrate when they are hit
Vocal cords vibrate when we talk, sing, or shout

If something is not vibrating, it cannot make a sound.

Make your own instrument

Tie the elastic bands around an open box.
Try plucking the bands.
How do they sound? Did you notice that the small elastic bands have a different pitch to the large ones?

How are sounds made?
Sounds are made when objects vibrate. The vibrations enter your ear and you hear them as sound. Find out more about how sound travels.

How are sounds detected?
Sound waves make the eardrum vibrate and then send messages to the brain. Find out more about how the ear detects sounds.

Loudness and pitch

Sounds can be different in how loud or quiet they are, and how high or low they sound. These differences are caused by vibrations.

Loud and quiet sounds depend on the size of the vibration:

Large vibrations make loud sounds
Small vibrations make quiet sounds

For example, hitting a drum hard makes a louder sound than tapping it gently.

Pitch tells us whether a sound is high or low. Pitch depends on how fast something vibrates:

Fast vibrations make a high-pitched sound
Slow vibrations make a low-pitched sound

Short or thin strings vibrate faster and make high-pitched sounds. Long or thick strings vibrate more slowly and make low-pitched sounds.

Volume tells us how loud or quiet a sound is. Louder sounds are made when vibrations are stronger, and quieter sounds are made when vibrations are weaker.