When spacecraft orbit the earth, astronauts and everything inside appear to float as if they are weightless. While it might seem like the astronauts have escaped gravity, they are actually in a state of free-fall.
You might have experienced a similar feeling during a roller coaster ride with a vertical drop. When you feel yourself float up from your seat for a brief moment, you are experiencing this sensation. Astronauts can experience a continuous period of free-fall as long as they orbit the Earth. This works because the International Space Station (ISS) travels around at an average distance of about 250 miles (400km).
At this distance, the force of gravity is only 10% less than gravity on Earth’s surface, so the ISS is always being pulled downward. However, the ISS is also traveling forward at more than 17,300 miles (28,000km) per hour. The combination of these forces causes the path of the ISS to curve, and at that height and speed, the path of the ISS matches the curvature of the Earth. In this way, the astronauts never stop ‘falling’. This is known as microgravity.
This demonstration uses common household items to show how microgravity works. Start by predicting what you (or your students or kids at home) expect to happen when the cup (or bottle) is dropped.
What was different in the two demonstrations?
Suggested answer: In the second demonstration, the cup and the water are in free-fall together.
Why didn’t (as much) water flow out of the hole during free-fall?
Suggested answer: In free-fall, the water accelerates downwards at the same rate as the cup. The two were falling together, so no water fell out. The small environment of the cup and water experienced momentary microgravity.