Change the Size of a Shadow!
IntroductionHalloween is almost here and behind every corner there seems to lurk a spooky shadow! Luckily, this is all they really are—just shadows that are part of scary decorations set up to give you a thrill while trick-or-treating. But where do these shadows come from, and how can some of them be so huge? Do this activity and find out how to generate the scariest and largest shadow of all!
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
The saying “where there is a shadow there must be light” tells us that you need some kind of light source to generate a shadow. For example, your own shadow that constantly follows you around on a sunny day is generated by the sun. But shadows don’t necessarily disappear with the sun—other light sources such as the headlights of a car, the light of a table lamp, or a simple flashlight are able to cast shadows, too. All light sources emit light waves that travel away from their source. In optics, which is a special field of physics, this emitted light is modeled as a straight line called a light ray. A light ray indicates the direction in which the light travels.
To cast a shadow, you need an object that can block the light rays. Not every object is able to do that. Some materials will let the light pass through, while others will only block part of it. Objects that are able to block all the light are called opaque and will form a shadow. You also need a wall or screen on which you can make the shadow visible.
A shadow play is a good way to demonstrate how a shadow is cast. Shadows are projected on a screen, a light source is located behind the screen and the players, and cardboard figures are used to block the light rays. The light rays travel to the screen, which makes it look very bright. Shadows only appear on the screen once a player introduces a cardboard figure in between the light source and the screen. This is because the cardboard blocks the light traveling from its source to the screen, making the area behind it look dark instead of bright.
But how can you vary the size of a shadow? The closer an object is to the source of the light, the larger the shadow it casts. This is because an object closer to the light source will block a larger area of the light, increasing its shadow size. Try it out for yourself in this activity!
Extra: Play around with different objects. Choose different materials or different sizes. Do they all form a shadow? Why or why not? If yes, can you also make their shadows bigger and smaller?
Extra: Introduce a second light source by placing two flashlights in front of the wall. How do the shadows of objects that you put in between both flashlights and the wall look? How do they differ from shadows using just one light source?
Extra: Try to point your flashlight onto the object from different angles. How does the angle change the appearance of the shadow?
Observations and Results
Were you able to change the size of the object’s shadow? Before you could change the size of the shadow, you needed to generate it first. You probably didn’t see a shadow when you placed the object next to the flashlight and not directly into its path of light. This is because light travels in straight lines and as the object was not located in the direct path of light, it could not block the light from its source. However, once you placed the object directly in the path of light, you should have seen a shadow on the wall that had the same shape as the object. This time, the opaque object was able to block all the light from the light source, creating the dark shadow in the wall.
You should have observed that the size of the shadow decreased when you moved the object farther from the light source and increased when you moved the object closer to the light source. The explanation for this is that you simply block a much larger portion of the light from the light source when your object is closer, which increases the size of the shadow. Now you know how to make spooky Halloween shadows grow and shrink!
More to Explore
Light and Shadows, from toppr
Light does appear to travel in straight lines, from University of Leicester, UK
Shadow play, from Wikipedia
Science Activity for All Ages!, from Science Buddies
Svenja Lohner, PhD, Science Buddies
Science Buddies |
Optics, light, shadow
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