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Weightlessness in orbit
Beginner
Astronauts are in free fall, so apparent weight is zero.
Astronauts and spacecraft fall around the Earth together, so the contact force is zero: "apparent weightlessness". Gravity at the ISS is still 89% of the surface value.
Dropped objects appear to float.
Weightlessness ≠ no gravity.
In more detail
Astronauts in orbit feel weightless because they and the station are both in free fall around Earth. Gravity is still strong there, about 90% of its surface value.
Real-world uses
- Astronauts train in aircraft flying parabolic paths to simulate weightlessness.
- Microgravity experiments use orbital free fall to study fluids and materials.
- Astronauts float inside the International Space Station because they and the station are in continuous free fall around the Earth.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Is there no gravity in space?
No. Gravity is still strong, and it keeps the station in orbit.
Why do things float?
Because everything in the station falls freely with the station, so there is no contact force.
Is there no gravity in orbit?
No. Gravity is still about 90 percent of the surface value at station height, so the weightlessness is due to free fall.
Related topics in Gravitation & Orbits
Orbital period · Geostationary satellites · Polar and low Earth orbits · Kepler's first law · Kepler's second law · Kepler's third law