(Physics for ages 5+)
Have you ever slipped on ice? Or maybe you have tripped while running and skinned your knees. What is it that makes ice so slippery and the ground so rough? It’s called friction, and it is an important force that is always present for moving objects.
The video above shows one simple and fun activity to see how strong friction can be. Here’s what you need to do this activity yourself:
2 plastic bottles
2 wooden spoons or unsharpened pencils
Adult supervision (Adult supervision at all times please)
- Start by filling your 2 plastic bottles with rice. Use the funnel to slowly add rice to each bottle.
- When the bottles are full of rice, stab a wooden spoon (or pencil) into each bottle, handle first. Can you lift either bottle with the wooden spoon?
- Now, remove the wooden spoon from one of the bottles and pack the rice by pounding it on the table and squeezing the sides of the bottle. Please see the video for clarification.
- Reinsert the wooden spoon handle into the bottle with packed rice. Again, try lifting both bottles by pulling up on the wooden spoons. What happens this time? Were you able to lift either bottle?
Friction is the resistance of motion between when one object rubs on another. When you walk on slippery ice, there is very little resistance (friction), so your shoes easily slip. When you scrape your knees on the sidewalk, there is a lot of friction between the rough sidewalk and your skin.
In the case of the rice-filled bottles, there is very little friction when you pull the wooden spoon handles out of the bottles at first. After you pack the rice into the one bottle, the grains are so much closer together and when the spoon handle is reinserted, there is much more friction present.
In fact, there is enough resistance to pick up the bottle simply by pulling on the spoon.