How are shadows made?
Shadows are everywhere.
They’re dark patches of shade where light does not reach.
Light can travel through transparent objects, like glass,or translucent objects like this clear silicone lid.
But a shadow forms when an opaque, or non-transparent, object blocks light from passing through and reaching a surface on the other side.
Light travels in a straight line – that’s why shadows are the same shape as the object that makes them.Unless, of course, the object is at an angle.
Or the light shines from a different position.
Then the shape of a shadow can change too.
The size of a shadow depends on the distance between the light and the object.
The larger the distance, the smaller the shadow.
The smaller the distance, the larger the shadow.
You can use shadows to conduct experiments.
Using your torch like the sun, shine it on an object and draw around the shadow it casts on a piece of paper.
Now, move the torch closer, and draw around the shadow again.
You’ll see how, as the light got closer, the shadow got larger.
Did you know that half the world is always in shadow?
That's because the Earth travels around the sun, rotating on its axis.
The size of shadows changes throughout the day.
Early in the morning and early evening, when your part of the Earth is further away from the sun, shadows are at their longest.
But towards noon, as you get closer to the sun, shadows are at their smallest.
When the sky becomes cloudy, the sunlight that gets through is spread over a wider area.
The clouds soften or diffuse the light.
Diffuse light casts shadows that are softer and blurred around the edge.
If the sky is overcast, our shadows can seem to disappear completely!
So why do shadows matter?
Well, before clocks were invented, the ancient Egyptians used sundials to tell the time with shadows – three and a half thousand years ago!
We may have technology to tell the time now, but shadows are always there if we need them.
Nowadays, when flood lights shine on a football pitch from all directions at night, players can cast four different shadows at once!
But twice a year, people who live on the equator cast no shadow at all.
Zero shadow days occur when the sun is directly overhead.
Now you know about shadows – why not play a game?
Make a shape from a piece of scrap paper – but don’t show it to your friends.
Shine a torch on it and see if they can tell what it is, from the shadow that it casts.
Video summary
This short animated film explores how shadows are made.
A shadow forms when an opaque or non-transparent object blocks light from passing through and reaching a surface on the other side.
This film explains how the size of a shadow depends on the distance between the light and the object. The larger the distance, the smaller the shadow.
The fact that half the world is always in shadow is explored, and the way ancient Egyptians used sundials to tell the time with shadows – three and a half thousand years ago!
Teacher Notes
Explain
What are shadows? How are they made? What factors affect their size and shape?
Let’s explore shadows in more detail – and learn how to turn your shadow into a clock!
Key Facts
- Light travels in straight lines. Anything that blocks that light, casts a shadow.
- The shape and size of shadow depends on distance and angle to the light source. Multiple light sources cast multiple shadows.
- Objects can be classified as:
- Opaque - objects block all light.
- Translucent - objects partially block light.
- Transparent - objects allow light through.
- Shadows have been used for centuries to tell the time.
- Sundials are one example.
- This video references Egyptian Sundials.
- Further information on sundials can be found here: _
- This video references Zero Shadow Days. Further information can be found here:
Explore
Where to pause?
- 00:49 - pause the video: At this point, you can ask students to try the experiment whilst watching the video. They will need a piece of paper, a pen/pencil, an object and a torch. The room will need to be darkened.
- 02:20 - pause the video. Students can do the activity by following the instructions on screen. Make a shape from a piece of scrap paper. Don’t tell their partner what it is, shine a torch through it and see if they can guess what the shape is supposed to be.
Activities / Experiments
- Drawing shadows - use different objects to cast shadows with interesting shapes. Students try to imagine and associate the shadows that might resemble different animals.
- Puppets show - make card cut outs to create characters from their favourite story in English class. Students work in pairs or small groups to tell and present their stories.
- Shadow olympics - challenge students to see who can make the longest shadow or a shadow with the largest surface area, using just a torch and an object.
Fun Facts
- Before clocks were invented, people used sundials to tell what time of the day it was. As the Earth rotates on its axis, the sun appears to move across the sky, forming shadows that change its position throughout the day. The gnomon, which is the centerpiece of a sundial, casts a shadow that points to different directions on the flat plate. The markings around the plate then show an indication of what time it is.
Did you know?
- Sundials are certainly useful for the daytime when there is plenty of sunshine. You can turn yourself into a sundial too! To find north, look at the direction of the movement of the sun from east to west. Remember, you should never look directly at the sun. In the morning point your right arm in the direction of the Sun and and your left arm facing the opposite direction and then you are facing North. In the afternoon point your left arm in the direction of the Sun and and your right arm facing the opposite direction and then you are facing North. Once you find North, you may use your body as a sundial to read the length and direction of your shadow so you can estimate the time of the day.
Expand
Discussion questions:
- Does everything have a shadow? Are there any materials that do not cast shadows?
- Why does your shadow look so long at sunset?
- What makes a shadow bigger or smaller?
- How can a shadow be lighter or darker?
- Why do sports athletes in a stadium have several shadows?
Other ý resources
National Curriculum objectives:
- England: To use the idea that light travels in straight lines to explain why shadows have the same shape as the objects that cast them.
- Scotland: Predicts and investigates how the position, shape and size of a shadow depend on the position of the object in relation to the light source.
- Northern Ireland: To investigate the formation of shadows and how they change.
- Wales: To investigate how light travels and how this can be used.
Sources:
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What are air and water resistance? video
This film explains the difference between water and air resistance and demonstrates examples of how resistance plays a part in our everyday life.
Day and night. video
This film explores the difference between day and night and demonstrates how the rotation of the earth's axis contributes to making seasons such as summer and winter.
Mechanisms. video
This film explains what a mechanisms are, using examples of where they are used and how they make our lives easier.
What should I do with my rubbish? video
This film explains the impact waste is having on our planet and how we can work to reduce our rubbish to make a difference.
How to use scientific equipment. video
This film explains how we can use science equipment to develop our scientific abilities.
