Weightlessness
Astronauts feel weightless because they are in free fall.
About this topic
Astronauts in orbit feel weightless not because gravity is absent, since it is about 90% of the surface value at the space station's height, but because they and the station are in continuous free fall together. With no contact force pushing on them, there is no sensation of weight.
What we feel as weight is the normal force from the floor or seat, the apparent weight. In a lift accelerating downward the scale reads less than your true weight, and if the cable broke the reading would drop to zero, the same situation as the orbiting station. Zero-g aircraft, nicknamed vomit comets, fly parabolic arcs to give about 20 seconds of true free fall.
Worked example: a 70 kg person in a lift accelerating upward at 2 m/s² feels a normal force N = m(g + a) = 70 × 11.8 = 826 N, feeling heavier than their usual 686 N. Accelerating downward at 2 m/s², N = 70 × 7.8 = 546 N, feeling lighter.
Microgravity changes how fluids, flames and bones behave, so it is used for research on medicine and materials. Astronauts lose bone and muscle without exercise, so they train about two hours a day. The big misconception is that space has no gravity; the truth is that orbiting objects are falling around Earth, always missing it.
Key ideas
- Gravity still acts on them
- No normal force
- Orbiting is continuous falling
Quick check
Use cases: where Weightlessness helps
- Homework: review the key idea behind Weightlessness before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Weightlessness without notes.
- Visual learning: play with the interactive lab to see how Weightlessness changes when you adjust its inputs.
- Teaching a friend: explain Weightlessness in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Weightlessness?
Astronauts feel weightless because they are in free fall.
What will I learn in Weightlessness?
Gravity still acts on them. No normal force. Orbiting is continuous falling.
Is Weightlessness part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Weightlessness lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Weightlessness?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.