What does a cup full of water have in common with an astronaut? Not much, apart from the way gravity works on them both. Find out how with this experiment.
What You Need :
- A styrofoam or plastic cup
- Something to make a hole in the cup
- A bucket
- A garden or grassy area
What To Do :
1. Poke a hole in the side of the cup. If you use a plastic cup, you might need an adult's help because it'll be a bit trickier.
2. Cover the hole with your thumb and fill the cup with water.
3. Hold the cup up high and uncover the hole. You'll see that the water gushes out steadily.
This is one reason why it's good to do this experiment in the garden!
What do you think would happen if you let go of the cup? Would the water flow faster or slower out of the cup?
4. Hold the cup up high again and this time, let it drop! Now watch what happens.
Whats Going On:
When you let go of the cup the water stops coming out of the hole. It stays put until it hits the ground. The reason for this is that gravity works differently in different conditions.
When you're holding the cup, gravity pulls down on both the cup and water. But the only thing that moves is the water, because you keep the cup in place.
The water gets pushed against the bottom of the cup and the weight of the water forces it through the hole.
It's a different story when you drop the full cup from a height. Gravity pulls down on the cup and water equally and they fall at the same speed. As they descend together, there is no force pushing the water through the hole.
The same principle is at work when astronauts are in space. They appear to be weightless, but really gravity accelerates them at the same speed as the spacecraft. When the spacecraft is on the ground though, it's gravity that pushes on the astronauts and keeps them in their seats.