Physics in the Bathroom: Ripping Neatly
Have you ever gone into a bathroom to find that a child (or pet) in the house unwound toilet paper all over the floor? Next time don't blame him or her – blame inertia!
What you Need
- Full roll of toilet paper
- Toilet paper holder (or rod)
What to Do
- Put the toilet paper roll in a holder (like the one shown in the picture) or on the end of a pipe to keep it in place. There should be a small amount of paper hanging down.
- Pull on the end of the paper slowly and observe what happens. Does the paper rip?
- Let go of the paper and let the roll come to a stop. Tear off most of the extra paper, but leave a little hanging down. Now give the end of the paper a quick pull. What happens?
What’s Going On?
When you pull slowly on the paper the roll starts unwinding and should continue unwinding until you stop pulling. But when you pull quickly on the paper, it usually rips apart from the roll.
Objects like to continue doing what they are doing. If you roll a ball along the floor the ball will continue rolling until something causes it to stop – like a wall or friction. If you set a ball on the floor it will stay still unless something causes it to start rolling – like a push or gravity. This is inertia.
Pulling slowly on the paper gives the roll time to start moving. Once it starts moving, the roll continues moving along with the paper because of inertia. In contrast, pulling quickly on the end of the paper causes the paper to tear because the roll wants to stay still.
- Repeat the experiment, but use a roll of toilet paper that is almost gone. Does anything change?
- Investigate how the perforations in the toilet paper affect how it rips. Can you get the paper to rip in a place with no perforations?
- How does inertia affect other things in your bathroom - like running water and the clothes in the dryer?
- Kummel, Marc. An Experiment with Inertia.
- The Physics Classroom: Newton 's Laws
- Science Monster: Gravity and Inertia
- Toilet Paper World: Historical Facts