Balancing Act
Word of the day: balance
“Can you balance a ruler on one finger? What if I make one end heavy?”
Grab
- a ruler or paint stirrer
- a lump of play-dough
- a pencil or marker
Do
- Balance the ruler on their finger. Where does it balance? (The middle.)
- Stick play-dough on one end. Try balancing it in the middle now. It falls.
- Slide the finger along until it balances again. Which way did the balance spot move?
- Mark the spot with the pencil.
The big moment
Add the dough and the ruler drops off their finger.
Ask (guess first, then try)
- Why did it fall when we added the dough?
- Which way did the balance spot move: toward the heavy end or away?
What's going on (for you)
Every object has a balance point, its center of gravity, where its weight is even on both sides. Adding weight to one end pulls the balance point toward that end. It's the lever again: heavy and close balances light and far.
If they want more
Tightrope walkers carry a long pole to keep their balance point low and steady. Walk a line of tape on the floor with arms out vs arms in.
Look it up
Wikipedia: Center of mass PhET simulation