What happens when you drop a bunch of washers on the end of a string? Something amazing!
Materials:
- Length of string (30-40 inches)
- 16-18 medium-sized washers
- A friend to help out
To do:
Tie one washer to one end of the string and all the others to the other side of the string. Now, Have a friend hold their finger straight out and hang the end of the string with many washers over their finger. (See photo above). Hold the end with one washer out and away, and let go!
The end with one washer should swing around their finger and catch before the other end hits the floor.
What is the Science?
A pendulum is a weight suspended from a single fixed point above it so that it swings back and forth. You may have seen a pendulum in a grandfather clock. Normally, pendulums slow down and lose height as they swing, due to friction. In our pendulum, when you release the single washer, the weight of the other washers falling accelerates the single washer, rapidly decreasing the distance between it and the pivot point (the finger). This causes the pendulum to speed up and, as a result, swing faster, causing it to swing all the way around the finger. Friction from the string holds it in place, causing the falling washers to stop.
Ask Your Young Scientists
- How many times does the end wrap around the finger?
- Do you think this would work with other objects instead of washers?
- Why do you think we need so many washers on one end?
More to Explore
- Try changing the number of washers on the heavy end. How do more washers affect the pendulum? Fewer washers?
- Try changing the angle of the string before you let it go. How does that affect the pendulum?
- Can you try this with other objects?
Nick Villagra is a STEM Educator at the Connecticut Science Center, responsible for developing and delivering science experiences, including classroom lab programs, stage shows, and vacation camps. Nick holds a Bachelor of Science in Engineering from Swarthmore College. and has been a speaker at the New England Museum Association conference. Always looking to put a unique stamp on the Science Center’s offerings, Nick enjoys incorporating custom-designed 3D printed materials for students to interact with.
