Contrary to popular belief, there IS gravity in space

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

01 July 2007

Peter Wanjohi asserts that the “article…on why satellites maintain a circular orbit at constant speed left something amiss.” He goes on to say, “If the circular orbit is due to gravitational pull emanating from the centre of the Earth, it presupposes that gravity is a magnetic force. Yet we know that the Earth's magnetism is negligible...”

You are right Peter; the Earth’s magnetic force is extremely small compared to the planet’s gravity. But you are wrong in saying “…gravitational force emanating from the centre of the Earth presupposes that gravity is a magnetic force.”

First; gravity does not “emanate” from the centre of the Earth. It is a mutual pulling effect between any two masses – in this case, the Earth and the satellite. Every part of each object pulls at every part of the other. The effective direction of the combined resultant force is along the line joining the centres of the two objects.

For this reason, the gravitational force acting on a satellite (due to the Earth) is directed towards the centre of the Earth.

Conversely, the gravitational force acting on the Earth (due to the satellite) is directed towards the centre of the satellite. Remember; the two objects are pulling at one another, therefore, each “feels” a force due to the other.

Secondly, the fact that the force of gravity due to the Earth is directed to the centre of the planet does NOT “presuppose that gravity is a magnetic force”! Gravity is distinctly different from magnetism. The two are not interconnected – people are still searching for a connection through so-called Grand Unified Theories, or GUT’s, but no one has found any.

Magnetism arises from electric fields in motion – for that reason, it is more accurate to refer to it as the “electromagnetic” force. Gravity, on the other hand, is an innate property of mass. Anything that has some mass (however small) has a gravitational force field around it. The two forces can (and do) exist together around the same object at the same time. However, this does not mean that one produces the other!

The magnitude of the gravitational field increases if the mass gets larger and it decreases the farther away you are from the object. The gravitational pull only disappears when the object is infinitely far from any other. Clearly then, the popular notion that there is no gravity in space is a great fallacy!

Peter also adds another question: “you explained that the speed of a satellite is attained after it is accelerated by an external agent e.g. a rocket. Now who accelerates the space-walker to attain the same speed necessary to enable them repair or build the stations while floating around it?”

To answer that, we first ask ourselves how the astronauts get to space in the first place. Think about that for now; I will tie everything together next week.