When we think of astronauts floating freely inside the International Space Station, it’s easy to assume that there’s no gravity in space. But here’s the twist: gravity is very much present—even at the height where the ISS orbits Earth. So, why do astronauts feel weightless? The answer lies in understanding orbital motion and the fascinating physics behind “free fall. Here’s how it works:
1. Gravity Is Still Present
Even at the ISS’s altitude—about 400 km (250 miles) above Earth—gravity is still about 90% as strong as it is on Earth. This means the ISS and everything in it, including the astronauts, are constantly being pulled toward Earth.
2. The Concept of Free Fall
The ISS is moving at an incredible speed—about 28,000 kilometers per hour (17,500 miles per hour). This high speed means that as it falls toward Earth due to gravity, the curvature of its fall matches the curvature of Earth. Essentially, the ISS is falling around Earth rather than straight down to it.
3. Why It Feels Weightless
Since the ISS and the astronauts inside are both falling at the same rate, they don’t experience the normal “force” of gravity that we feel on Earth. This creates the sensation of weightlessness. In simple terms:
- On Earth, you feel your weight because the ground pushes up against you as gravity pulls you down.
- In the ISS, there’s nothing pushing up against the astronauts because both they and the station are falling together, creating the illusion that they are floating.
4. The Difference Between Microgravity and Zero Gravity
The term “microgravity” is more accurate than “zero gravity.” It means that the gravitational forces are very weak but not completely absent. What astronauts experience is essentially continuous free fall, which feels like floating because there’s no support force opposing gravity.
5. A Real-Life Analogy
Think of riding a roller coaster: as the coaster descends rapidly, you feel a brief sensation of weightlessness because both you and the coaster are accelerating downwards at the same rate. In space, this effect is constant, creating the feeling of floating all the time.
So, astronauts aren’t floating because gravity doesn’t exist—they’re floating because they’re in a constant free fall around Earth.
Name : Abhishek Agrawal
Department: Physics Foundation
Narayana Jaipur Center (NIHQ)