Tick! Tock! Ever seen an old grandfather clock? That thing swinging back and forth is a pendulum. In fact, anything that has a weight that pivots and swings freely is a pendulum. A string with something tied to its end, even you on a swing set on the playground are considered a pendulum. This month we’re going to construct a pendulum and experiment with what will make it swing faster or slower.
- A tall cup (one you can’t see through), a penny, tape, water, wax paper, a magnifying glass or a pair of prescription glasses (with your parents’ permission!)
Experiment #1: Reappearing Penny
Cup, penny, water
Procedure part 1:
Place a penny in the middle bottom of a non-see-through cup (stick it there with a small piece tape)
Stand in a place where you can see inside the cup but can’t quite see the penny in the bottom of the cup (the top of the cup will block it)
While standing in the same place, have someone start to fill the cup up slowly with water. Observe when you can spot the penny just with the addition of water.
Explanation: Did you know you see things because light is bouncing off of them and you’re your eyes? Refraction is the bending of something as it travels through a different material. We will talk about light bending, but there are other things like sound waves and seismic waves (earthquakes) that also refract. Light will change the angle it moves as it goes through air into water, or vice versa. As you fill the water into the cup the light ray from the penny is bent until it can then reach your eye.
Experiment #2: Wax Paper Lens
Procedure part 2:
Cut a piece of wax paper out and place it over some fine print
Put a single drop of water on top of the wax paper and move the paper around on top of the print
Watch to see how the letters change as you move the water drop over them
Explanation: As in the first experiment, water refracts the light going through it. It is acting as a magnifying lens and causing the light to bend out from the letters, making them appear bigger. Experiment with different sized drops of water. Does this change the size of the letters? Did you know this is how glasses work? The lens will bend the light and make images get bigger or smaller, depending on the prescription. If you have a magnifying glass or if you ask your parents permission to borrow their glasses or even if you have your own, hold them over a piece of paper with words on it to see how you can change the size of the letters. The curve of the glass will cause the light to be bent, or refracted!
Now that you have an idea of how refraction works, see if you can think of different ways to make a magnifying lens with water, or make other tricks like the penny experiment. Does sugar water or salt water change how big letters get if you look through it compared to plain water? Good luck, and keep experimenting.
Steve Davala is a high school chemistry and physics teacher who likes to write. He’s got two kids of his own and subjects them to these science activities as guinea pigs. Follow him on Twitter @sdavala or email him at firstname.lastname@example.org.