The concept of ‘zero-G’ in space is something that most are familiar with, with astronauts floating around in the ISS being a familiar sight.

Contrary to popular belief, however, astronauts do not experience this microgravity environment due to them being too far away from the surface of the Earth.

In fact, at the orbital altitude of the ISS, Earth’s gravity is still around 89 per cent the strength of gravity on the ground.

However, because the ISS is travelling at a speed of 27,000km/h, it moves fast enough for the centripetal force from circular motion to exactly balance against Earth’s gravity at its altitude, thus remaining in a stable orbit – while it freefalls through one kilometre, it simultaneously travels 12.5 kilometres horizontally, meaning that as the Earth’s surface curves beneath it, it does not actually lose altitude.

This state of perpetual freefall is what leads to microgravity inside the ISS.