Image © Riccardo Annandale, under a Creative Commons license.
Light and shadow surround us every day (some days undoubtedly more than others - I'm looking at you British summer!) and are essential to survival on planet earth.
We may see them all the time, but that doesn't mean it's easy to understand just how and why they exist, or explain them to inquisitive youngsters. Luckily, our simple guide breaks down light and shadows and how you can explain these terms to your little science whizz.
In KS2, children learn that light is a form of energy providing food for plants and enabling us to see everything around us. It's also found in many man made light sources such as televisions and light bulbs. This guide will explain how light and shadows behave when it comes to objects and the visual tricks science might play on us.
What Is Light?
Light is a form of energy that travels in straight lines. The strength of the light depends on the energy in these lines.
A main source of light for life on earth is the sun. The sun generates a huge amount of energy which travels down to us in straight lines of light, enabling us to see everything around us. It also provides energy and warmth that allows plants to grow and keeps animals alive.
What Is A Shadow?
The way light travels will determine how we see it. Because it travels in straight lines, it will keep going until it hits something. If it is a shiny surface, it will be reflected. However, if it is solid, it won't be able to bounce off and instead, darkness will appear. This darkness is known as a shadow.
A shadow appears when an object that we can't see through blocks the source of light. Materials that don't let any light through are known as opaque. This could be something made of materials, like a house, or something that exists in nature, like a plant. The opposite of an opaque material is a transparent one, something that you can see straight through.
The shape of the shadow will always be the shape of the object that has blocked the light source. However, shadows will be different sizes depending on where the light source is coming from and its distance from the object. The closer an object is to light, the bigger the shadow will be. You can test this by holding a household object up to a lamp and testing the size of the shadow depending on how close it is to the light source.
A great way to remember how shadows are formed is to use this acronym:
SOS: Source, object, shadow.
How Are Light And Shadow Related?
Light and shadows are always connected because shadows are the absence of light.
A light source that causes shadows is the sun. The position of the sun in the sky determines the appearance of shadows. When the sun is directly above an opaque object (like it often is during midday), shadows are shorter. This is because the light from the sun is travelling to objects at a different angle. In the morning and afternoon, shadows are longer.
Because of this, we can use shadows in sundials to tell the time. The shadow will move around the sundial as the sun moves around the sky, pointing to different numbers that represent the hours of the day.
What Is The Difference Between A Shadow And A Silhouette?
What happens when the light is brighter behind an opaque object so the object itself appears dark? This is known as a silhouette. The objects may be in darkness, or only their outline visible, but we can still see the background behind it. It's helpful to imagine a skyline of buildings with a sunset behind them, where the buildings appear dark and two-dimensional in comparison to the bright sky.
Here, there is an absence of light on the buildings that means they cannot be seen properly, but the brightness of the background creates a silhouette or outline.
What Are Children Taught In School About Light And Shadows?
For the KS2 science curriculum, children will learn the basics of how light travels and shadows are formed. They begin to learn about this in Year 3, by the end of which children should understand that light enables us to see things and that shadows are formed when light is blocked. By Year 6, students should understand that light travels in straight lines and use this knowledge to explain the shape of shadows.
Activities For Learning About Light And Shadow
It can be helpful to illustrate lights and shadows to children using visual learning and materials around the house. Why not search for some objects you could hold up to a light source (keeping fingers away from hot light bulbs, of course)?
Or pick a sunny day and head out on a walk, search for some objects with shadows and discuss why this might be. If you've got more time on your hands for a science-themed arts and crafts afternoon, why not craft some shadow puppets from household materials to hold up to the light and see how the different movements affect the shape and size of their shadow?
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