You will need
- 1 Plastic bottle (500 ml)
- Rice (you can still eat it after the experiment)
- 1 Funnel
- 1 Chop stick or pencil
What to do
- Fill the plastic bottle to the rim with rice. You can use the funnel to help you.
- Pick up the bottle and hit its bottom against the table several times. This will compact the rice more and let air escape.
- There is some more room in the bottle now. Add more rice until it reaches the rim of the bottle.
- Now insert the chop stick or pencil into the rice. Push it down as far as you can.
- Take a hold of the chop stick or pencil and lift it up. What happens?
There are different forces acting on the bottle. The force of weight or gravity pulls it down to Earth. When you insert the chop stick or pencil into the rice, there is an additional force of friction between the rice and the chop stick/pencil. The force of friction acts in the opposite direction of gravity.
If the forces of gravity and friction are equal, you are able to pick up the bottle when only holding on to the chop stick/pencil. If forces are equal and act in opposite directions, we say that they are balanced. In this experiment the forces of friction and of gravity are balanced.
You can watch a video of this experiment here: