But I Don't Want More Heat!

Now that you've learned that rubbing objects produce heat let's experiment a little further. If heat is caused by the tiny particles in each object colliding, will different types of objects make more or less heat?

Look at this close-up picture of wood. Does the surface look smooth or rough?

Now compare that surface to a close-up of this piece of sand paper.

Do you predict that rubbing a smoother surface or a rougher surface will produce more heat?

TRY IT OUT!

Materials:

• Science journal or paper
• Assorted smooth and rough objects:
  • craft sticks
  • rocks
  • sandpaper

Procedure

1. Record your prediction of what happens when you rub together each combination of objects.
2. Rub together the various objects.
3. Record the result of rubbing each combination of objects.

Caution: Rubbing rough objects on something may cause damage to the object. Get parent or adult permission before using items.

Your chart could look something like this:

If you discovered that rougher surfaces produce more heat, you're correct!

Let's review what we've learned so far.

1. When objects are rubbed, they produce heat.

2. Rougher surfaces produce more heat than smoother surfaces.

What if you don't want heat? Sliding down a slide in your swimsuit isn't much fun because your legs keep sticking to the slide and heat is produced. A smart person invented the water slide, because water will lubricate, or smooth the surface, and you will go down quickly and easily.

Putting lotion or water on your hands will also lubricate your hands, and you won't produce as much heat when rubbing.

Machines with many moving parts will usually use oil or water to reduce the heat being made from parts rubbing together.

The last thing we've learned, then, is that a lubricant can reduce the amount of heat. Try an experiment with your class or family to see how this works. Have everyone start to quickly rub their hands together. Stop everyone so they can feel the heat. Put lotion or water on some of the hands, then have them quickly rub again. Is there as much heat? Why or why not?

For further exploration, try to find other materials that will lubricate. If you're really brave, try things like small amounts of butter, peanut butter, pudding, sugar, chocolate milk powder, or whipped cream (with adult permission, of course!)

Let's review what you've learned. Look at each picture, then click the button telling if more or less heat will be produced.

Object	Amount of heat produced