This month we’re going to experiment with a force that affects us all the time: gravity! Gravity is a force that all objects exert, but you can really only feel it from the really big things. The Earth pulls us down to its center. The Moon pulls our water from the oceans to make the tides. The Sun keeps all the planets in orbit with its gravity. The bigger the object’s mass, the more gravity it exerts.
Gravity is what makes us feel our weight. We would weigh less on the moon, because it has less gravity. We would be a lot heavier on Jupiter because it has more gravity.
So now we come to our experiment. We’re going to see what gravity can do to a stream of water as it falls.
- A paper or Styrofoam cup,
- water in a pouring container,
- a large bucket or just the outside grass.
- Make sure you are doing this experiment over a large bucket or outside as water will spill
- Poke a hole in the paper cups near the bottom on the outside of the cup
- Fill the cup with water but keep your finger over the hole
- Take your finger off the hole and observe what happens to the water. It should pour out in a nice steady stream. If not, re-poke the hole and refill the cup with water
- Fill the cup again and hold your finger over the hole. This time, you are going to drop the cup and let go of the hole at the same time and observe what will happen to the water! Make sure the cup falls into a large bucket or onto the grass. Make a guess about what you think will happen!
- You should notice that when you drop the cup the water no longer sprays out the side of the cup. Can you guess why?
- First off, when you just held the cup and let your finger off the hole, the water was pulled down by gravity and thus water pressure pushes it out the hole.
- So what changes when you drop the cup and water? The cup and water begin falling at the same speed, and are actually weightless as they fall.
- Cool, huh? There is no water pressure on the cup as it falls because both the water and the cup are moving at the same speed.
What experiments can you try with gravity? How fast do different objects fall? Grab a tennis ball and a basketball and drop them from the same height and the same time. What do you notice? How about a shoe and a ping pong ball?
Experiment with lots of different objects. You will find that sometimes objects drop at the same rate, and other times not. Want to know why? Check out the author’s web site below for a detailed post on it!
I hope you enjoyed this simple experiment. If you have more questions about this, or need tips about science fair ideas around this topic (or others), contact the author.
Steve Davala is a high school chemistry and physics teacher who likes to write and work with Photoshop. He’s got two kids of his own and subjects them to these science activities as guinea pigs.