Physics: Balancing Act: Levers, See-Saws, and Center of Mass
Explore how levers balance and why weight and distance matter
Physics: Balancing Act: Levers, See-Saws, and Center of Mass
Explore how levers balance and why weight and distance matter
Physics - Grade 2-3
- 1
Two children sit on a see-saw. One child sits close to the middle, and the other child sits far from the middle. If they weigh the same, which side will go down?
Think about pushing a door near the handle instead of near the hinges.
The side with the child sitting farther from the middle will go down because being farther from the balance point gives more turning force. - 2
A pencil balances on your finger when your finger is under its middle. What is the middle balance point called?
The middle balance point is called the center of mass. It is the place where the pencil can balance. - 3
Mia puts one toy block on the left side of a ruler and one same-size toy block the same distance from the middle on the right side. What will happen to the ruler?
Balance can happen when both sides match.
The ruler will balance because both blocks have the same weight and are the same distance from the middle. - 4
A heavy book is on one side of a see-saw. A light stuffed animal is on the other side. If both are the same distance from the middle, which side will go down?
The side with the heavy book will go down because it has more weight at the same distance from the middle. - 5
Sam wants to lift a heavy rock using a stick as a lever. Should he place the small support closer to the rock or farther from the rock to make lifting easier?
A lever can make work easier when the support point is placed in a helpful spot.
He should place the small support closer to the rock. This gives his end of the stick more distance to push down and makes lifting easier. - 6
Draw or describe where you would put your finger to balance a spoon. Explain your answer.
You should put your finger near the spoon's center of mass. For many spoons, this spot is closer to the bowl of the spoon because that end is heavier. - 7
A see-saw is perfectly balanced. Then one child slides closer to the middle without anyone else moving. What happens to that child's side?
Moving closer to the middle gives less turning force.
That child's side becomes lighter in turning force and may rise because the child is now closer to the balance point. - 8
Look at a ruler balancing on an eraser. A coin is 2 inches from the middle on the left. Another same coin is 4 inches from the middle on the right. Which side will tip down?
When the weights are the same, the one farther from the middle has more effect.
The right side will tip down because the same coin is farther from the middle on that side. - 9
Why is it easier to balance with your arms stretched out like a tightrope walker?
It is easier because stretching your arms out helps spread your weight and lets you make small changes to keep your center of mass over your feet. - 10
A big dog and a small cat are on a see-saw. The dog is close to the middle. The cat is far from the middle. Tell one way they might make the see-saw balance.
A lighter object can balance a heavier object if it is farther from the middle.
They might balance if the heavier dog stays close to the middle and the lighter cat sits far from the middle. The cat needs more distance to help match the dog's weight.