Why do things slide?
Hypotheses: Ask children why we slide on ice but not on pavement. Ask them to name materials which are slippery and others which aren't. If they have limited ideas, you may name various materials and have them tell you if they are slippery or not. What makes a surface slippery?
- A wooden plank
- A smooth plastic tray (large)
- Objects made of various materials which provide a flat surface (eraser, penny, a die, a piece of cardboard, a small plastic plate, etc.)
- An ice cube
- Hand soap and water
This experiment is made up of three sets of brief manipulations. They may be executed one after the other or separately.
- Align all the objects, except the ice cube, at one end of the wooden plank.
- Gently raise this end of the plank until the objects begin sliding. Which objects slide easily? Which ones stay put?
- Repeat the same manipulations, placing the objects on the plastic tray instead of the wooden plank. Is there a difference? Is the result the same?
- Gather all the objects, including the ice cube. Stand next to a large, smooth table which does not have any other items on it.
- One after the other, try to make the objects slide on the table. Which one slides best? Which one slides the least?
- You will not need the objects for this part of the experiment. You will only need your hands, water, and a small quantity of hand soap.
- Rub your hands together, gently at first and then more quickly. What do you feel?
- Next, wet your hands and add a small amount of hand soap. Rub your hands together again. What happens?
Explanation: When two things are rubbed together (like the objects on the smooth surface or your hands), an invisible force is created. This invisible force tries to stop the movement. It is called friction. It acts a little like invisible glue.
In the first set of manipulations, the smoother objects slid easily on the wooden plank. There was less friction between their surface and the plank's surface. For the same reason, the objects slid even better on the plastic surface.
In the second set of manipulations, you noticed that the ice cube slid much better than the other objects. Do you know why? Upon melting, the ice cube left a thin film of water between its surface and the table. This film reduced friction, enabling the ice cube to move quickly.
In the third set of manipulations, you felt warmth when you rubbed your hands together. The more you rubbed, the warmer your hands felt. This warmth is the result of friction between your hands. When you did the same thing with wet, soapy hands, the water reduced friction (just like the ice cube, remember?) so heat production was also reduced!
a Bachelor's Degree in Biological Science. She has worked in a
laboratory and tested her knowledge. She has taught Math, Chemistry, and
Physics. She has also developed a simplistic and innovative approach
designed to introduce young children to scientific experiments, old and
new. She created her friend Globule. This character is sometimes red,
and sometimes white. He guides little ones through their scientific
experiments and discoveries. It is clear to see Angélique is passionate
about children and science. Globule's Approach.