Friction You Can Feel

Grab these first

• small smooth object such as a coin, smooth stone, or plastic game piece
• three surfaces: smooth floor, small bath towel or piece of fabric, sheet of sandpaper or rough cardboard
• masking tape or painter's tape to mark a starting line
• tape measure or ruler
• paper and pencil for recording distances and drawing

1. 1

   Explain the idea

   Friction is a force that happens when two surfaces rub against each other. It always pushes in the opposite direction of motion, so it slows things down. The rougher the surfaces are, the stronger the friction becomes.

   Think about sliding your hand across a smooth table versus across a carpet. On the table there is very little rubbing, so your hand glides easily. On the carpet the tiny fibers catch and tug, creating more friction and making your hand stop sooner.

   The amount of friction also depends on how heavy the object is and how fast it is moving, but today we will focus on how different surfaces change the friction. We will test this by giving the same object the same push on three surfaces and measuring how far it travels before friction stops it. The surface that creates the most friction will make the object stop in the shortest distance.

2. 2

   Gather the materials and find a flat, clear floor space about six feet long. Place the three surfaces next to each other so they are easy to slide across in turn. Talk with Theo about what he already knows about things slowing down or speeding up, and tell him today you will discover how friction is the invisible force that does most of that slowing.

3. 3

   Explain the concept above in your own words. Then demonstrate the test once on the smooth floor: set the small object at the starting line, give it the exact same gentle push each time, and let it slide until it stops. Use the tape measure to record how many inches it traveled. Have Theo repeat the test two more times on the same surface and write down each distance so you can find the average later.

4. 4

   Now let Theo run the same test on the towel surface and then on the sandpaper surface, always using the same starting push. He should do three careful trials on each surface, recording the inches traveled each time. Remind him to keep the push exactly the same so the only thing changing is the friction from the surface.

5. 5

   Look at the numbers together. Ask Theo which surface let the object slide the farthest and which stopped it soonest. Guide him to see that the surface with the shortest distances created the most friction. Talk about why: the towel fibers and sandpaper bumps rub harder against the object than the smooth floor does.

6. 6

   Have Theo draw a quick comic-strip panel showing the object sliding on each surface, with little friction arrows showing where the rubbing happens. Then ask him to explain in one sentence what he learned about friction and how it changes motion.

7. 7

   Do this together

   Theo will run the sliding test on all three surfaces and create a simple three-panel comic that shows the object traveling different distances because of different amounts of friction. In the first panel the object zooms far on the smooth floor with almost no friction arrows. In the second it stops sooner on the towel with medium arrows. In the third it barely moves on the sandpaper with big, angry friction arrows. This lets him turn the numbers into a fun visual he can show the family later.