# Misconceptions in Physics

### By Pratik Choudhury

(Test Preparation (ACT/SAT/SSAT), IGCSE/MYP Math & Physics, IB Physics tutor at The Edge Learning Center)

There is a common misconception that ‘There is no gravity in outer space’. This misconception gets further reinforced when phrases such as ‘zero’ and ‘micro’ gravity are often heard in videos that show humans floating around in their space suits.

Gravity is based on the mutual attraction between two objects, and the strength of that pull depends on both mass and the distance between them. Greater the mass, greater the gravitational pull.

Newton’s law of universal gravitation expresses the proportionalities of the force, mass and distance between two objects as validated by the following mathematical expression:

and  represents the respective masses of the objects and  the distance between them.

is known as the universal gravitational constant.

According to the above formula, the force of attraction between two objects is inversely proportional to the distance between them. As such, when the distance between two objects increases the force between the two objects decreases and vice versa. This law holds true between any objects in the universe: the stars, the planets, and even between humans (just that the force experienced is insignificant for us to feel it). So as long there exists a considerable distance between two objects, there will exist a force of attraction between them. In a liner, greater distance leads to rapidly diminishing gravitational pull.

Any object placed at a higher altitude above earth’s surface will experience a lesser pull of earth’s gravity compared to one experienced on earth’s surface.

For example, ISS (International Space Station) roams some 220 miles (354 km) above earth’s surface. To some, the space station might be situated at a fairly good distance from Earth’s surface for Earth’s gravity to have any effect on it, but in reality the force of gravity is about 90 percent of that on the Earth’s surface.

Another way of looking into the effect of earth’s gravity on ISS is to understand why the space station revolves around the earth at a blistering speed of 17,000 to 18,000 mph (which is 10 times the speed of an average bullet) in the first place. The answer is simply to be able to counter Earth’s gravity and stay aloft. In reality, the astronauts and the space station are free falling under earth’s gravity. On Earth, gravity is constantly pulling us down. The floor or the ground that supports us stops us from falling resulting in experiencing weight as we press against it.

Any ship in orbit around the Earth is falling slowly to Earth as there is no ground or floor to stop them from falling. Since the ship and the astronauts in it are falling at the same speed, they feel weightlessness and simply float around, and hence leading to the phenomenon called ‘Zero Gravity’.

In summary, ‘Zero Gravity’ doesn’t mean that gravity is zero, but simply a state or condition in which there is no apparent force of gravity acting on a body because both the body and its surroundings are freely and equally accelerating under the force.

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