Is There Gravity on the Moon or in Space?
Yes, Gravitational Forces Exist Everywhere in the Universe
Mar 3, 2009
Many people think that there is no gravity either in space or on the Moon. That is however incorrect according to Newton's law of universal gravitation.
Newton's Law of Gravity
Newton's law of gravity states that there is an attracting gravitational force between any two objects in the universe. The force will be greater for more massive objects. The gravitational force will decrease as the distance between two objects increases. The gravitational force from very distant objects will be weak but not zero.
For purposes of Newton's law of gravity, the distance between two objects is measured from the centers of the objects. For example on Earth's surface the distance to Earth is the Earth's radius, because the distance is measured from Earth's center.
Gravity On the Moon
There is gravity on the Moon. The gravitational force on the Moon is weaker than on Earth, however it is there. The gravitational field on the Moon is one sixth as strong as on the Earth. So an astronaut who weighs 180 pounds on Earth will weigh ((180/6) pounds =) 30 pounds on the Moon.
This weaker gravitational force is why astronauts in videos taken from the Moon's surface bounce so high when they walk. However they still come back down because the gravitational force is still there. The Moon's weak gravity is also the reason that the Moon does not have an atmosphere.
The gravitational force on the Moon's surface is less than on Earth's surface because the Moon is much less massive than Earth. The Moon has a smaller radius, that would tend to make the gravitational force larger, but in this case the effect of the smaller mass dominates so that the gravitational force on the Moon is less than on Earth.
Gravity in Space
Astronauts orbiting the Earth in the space shuttle are weightless, so people might think that there is no gravity in space. However this can not be true because Earth's gravity is what keeps the shuttle orbiting Earth.
The space shuttle orbits Earth at an altitude of only a few hundred miles and Earth has a radius of a few thousand miles, so shuttle astronauts are only a little farther from Earth's center than their friends back home. Astronauts are weightless because they are in freefall not because there is no gravity in space.
What about very deep space very far from any stars or galaxies, for example, halfway between here and the Andromeda galaxy? One might think that there would be no gravity this deep in space. The gravitational force would be very weak, but it would not be exactly zero. In fact the gravitational force between galaxies often causes them to mutually orbit each other.
There is still a weak gravitational force in very deep space because the gravitational force gets smaller as the distance increases, but it never reaches zero. Hence in very deep space gravitational forces are very weak, but they are still there.
Compared to the other fundamental forces of nature (electromagnetic force, strong nuclear force, and weak nuclear force) the gravitational force is quite weak. However the gravitational force is the most far reaching of the fundamental forces. Gravity exists everywhere in the universe - including on the Moon and in space.
 |
