Light and shadows

We are surrounded by sources of light.

The Sun is our main source of natural light but we also get light from artificial sources such as ceiling lights, lamps, torches, candles and even electronic devices like phones and televisions.

Light travels in straight lines and will keep going until it is blocked by an opaque object, which does not let any light pass through it.

light cannot pass through the object, and cannot bend around it, so it bounces back off the object.

As the light cannot get to the space behind the object this creates a dark area called a shadow.

Not all shadows are the same size or shape.

The size and shape of the shadow matches the size and shape of the object that is blocking the light (as long as the light is pointing straight at the object).

A person will make a person shaped shadow, and a giraffe will make a giraffe shaped shadow! But there are other things that affect the size of a shadow.

Have a think about the different sizes of the shadows in the video.

1. Why are some shadows bigger than others?
2. Do any shadows change in size?

1. Larger objects produce larger shadows. This is because it is blocking more of the light. If the light source is close to the shadow, this also leads to a larger shadow.
2. Some shadows, like the palm trees, change in size. This is because the distance from the light sources changes.

What did you find out?

Shadows are changed by:

• The size of the object.
• Whether the light source is moving or still.
• How close the object is to the light.
• How high the light source is.

• Sundials were first used to tell the time thousands of years ago. Many people still have them in their gardens today.

• Half the world is always in shadow because the Sun's light can only reach the side of the Earth which is facing it.

• If the object is further away from the light source, the shadow is smaller.

• Some objects, such as glass, are transparent and don't make a shadow. Light can shine through them. Some light shines through translucent objects, such as a balloon or sheet of wax paper.

• Light travelling through space is usually in a sharper focus, as it doesn't travel through an atmosphere.

• When a shadow is cast by the Earth onto the Moon, it is called a lunar eclipse.

• A solar eclipse occurs when the Moon passes between the Sun and Earth, blocking the Sun's light and forming a shadow.

• Shadows are generally longer in the winter as the position of the Sun is lower in the sky.

The size of the object

If the same light source was shining on two objects from the same distance away, a bigger object would create a larger shadow and a smaller object would create a smaller shadow.

If an object changes size when the light is shining on it, such as with a balloon inflating, then the shadow will change size too.

Whether the light source is moving or still

If both the light source and the object stay still then the shadow will stay still too.

But if the light source begins to move then the shadow will change, either by changing the direction in which the shadow is pointing (it will always be behind the object, on the opposite side that the light source is) or by changing the length or width of the shadow.

You can see this by looking at the shadow of a tree throughout the day as the Sun moves across the sky.

How close the object is to the light

If an object is close to the light source then it will create a bigger shadow.

This is because the object is blocking more of the light. If the light source is further away then it will create a smaller shadow because it is blocking less of the light.

How high the light source is

if the light source is close to the ground and pointing to the side of the object then this will create a long shadow that comes out of the opposite side of the object.

As the light source moves higher the shadow will become shorter and shorter until the light source is high up and pointing straight down onto the object, where there will be no shadow at all that you can see.

This is shown when the Sun rises, travels overhead and sets at the end of a day; the shadows will be longest in the morning and evening, and shortest at midday.

Did you know?

If an object is opaque like a person then this will create a dark black shadow because no light can pass through at all.

If an object is translucent then the shadow will be much paler and be more grey than black because some light is passing through.

If an object is transparent, like a window or a glass it won’t make a clear shadow at all as the light can travel through it.

Light – Beams that can be seen by the human eye. Light travels in straight lines and will keep going until it is blocked by a solid object.

Opaque – Opaque means something that does not allow light to pass through it and cannot be seen through.

Translucent – Translucent means the material will allow some light to pass through it but objects on the other side will not be clearly seen.

Transparent – If an object or material is transparent, it means light completely passes through it, and you can see clearly through it.

Shadow – A shadow forms when an opaque or non-transparent object blocks light from passing through it and reaching a surface on the other side.

• Choose an opaque object which will make a shadow.
• Move the object nearer or further away from a light source.
• Measure the length of the different shadows.

You could record your findings in a table like this.

• Try it with a different object.
• What did you notice? Did you change the size of the shadow?