Amaze your friends and family with a science show. Ask your audience to predict the outcome of each of these easy science experiments about gravity.
All objects on Earth are pulled toward the planet’s center by the force of gravity. Gravity is the force that makes a basketball swish through a hoop. Gravity is the force that makes your glass of juice crash to the floor when it slips out of your hand. Gravity is the force that keeps your feet on the ground when you go for a walk. As Judy Breckenridge points out in Simple Physics Experiments with Everyday Materials, “Without gravity we would all float off into outer space.” Hooray for gravity!
Science Experiment: Gravity and Air Resistance
Contents
Before performing this experiment, show your audience a shoe and a flat piece of notebook or copy paper. Explain that you will be dropping both objects from the same height. Then ask your audience these questions:
- Who thinks the shoe will hit the floor first?
- Who thinks the paper will hit the floor first?
- Who thinks both objects will hit the floor at the same time?
Experiment:
- Hold the shoe in one hand and the paper in the other.
- Hold both objects high in front of you at equal heights.
- Release both objects at the same time.
Observation: The shoe hits the floor first.
Explanation: Because of the paper’s shape, its fall is slowed by air pushing up against its under-surface – this slowing effect is called air resistance.
Science Experiment: Gravity and Weight
Before performing this experiment, show your audience the shoe and the piece of paper crumpled into a ball. Explain that you will be dropping both objects from the same height. Then ask your audience these questions:
- Who thinks the shoe will hit the floor first?
- Who thinks the paper ball will hit the floor first?
- Who thinks both objects will hit the floor at the same time?
Experiment:
- Hold the shoe in one hand and the paper ball in the other.
- Hold both objects high in front of you at equal heights.
- Release both objects at the same time.
Observation: The shoe and the paper ball hit the floor at the same time.
Explanation: Even though the earth exerts more pull on a heavier object, a lighter object experiences a greater degree of acceleration, meaning that it moves at a greater speed. Consequently, objects of different weights fall at the same rate when other forces such as air resistance are not a factor.
Science Experiment: Center of Gravity
Now it’s time for audience participation in your science show. Ask for volunteers for each of these exercises involving the center of gravity:
Pick up a penny
Ask a volunteer to stand against a wall with his feet together, heels pressed against the wall. Place a penny about one foot away on the floor in front of him. Ask him to pick up the penny without moving his feet or bending his knees. Can he do it?
Lift your left foot
Ask a volunteer to stand with her right side against a wall, pressing her right foot and cheek against it. Instruct her to lift her left foot off the floor. Can she do it?
Jump forward
Ask a volunteer to bend forward and grab his toes, keeping his knees slightly bent. Tell him to jump forward without letting go of his toes. Can he do it?
Stand up
Ask a volunteer to sit in a straight-backed chair. Tell her to keep her back straight, her feet flat on the floor, and her arms folded across her chest. Then ask her to stand up. Can she do it?
Observation: Because all of these tasks restrict the center of gravity, it’s almost impossible for a person to perform any of them.
Explanation: As far as gravity is concerned, the weight of an object is concentrated at a single center point. The center of gravity for an object with a regular shape – the Earth, for example – is located at its geometric center. However, in irregularly shaped objects – the human body, for instance – the center of gravity moves around. If you try to shift too far away from your center of gravity, you’ll lose your balance.
Learning new things about the world around you is fun and exciting. It’s even more fun when you share your discoveries with your family and friends. Gravity is just one of the interesting forces of nature – there are many more to explore and share.
Sources:
- Bardhan-Quallen, Sudipta. Championship Science Fair Projects. NY: Sterling Publishing, 2004.
- Breckenridge, Judy. Simple Physics Experiments with Everyday Materials. NY: Sterling Publishing, 1993.
- Cobb, Vicki. Bet You Can’t! NY: Lothrop, Lee & Shepard Books, 1980.