Is gravity a force or an acceleration?

Question

This sounds really stupid (especially from someone who got an A in Physics at A-Level), but I understand it as both.

All mass has gravity. Therefore the huge mass of the earth exerts a force on us, pulling us into it. Gravity is therefore a force.

We have weight due to gravity. This is equal to our mass multiplied by the acceleration due to gravity. BUT if you assume the Earth is not spinning, when we are standing on the ground, we are not accelerating towards the centre of the Earth.

Of course, the Earth is actually spinning, which creates centripetal force, and so we are accelerating towards the centre of the Earth. BUT the geometric poles (i.e. not magnetic poles) do not have any centripetal force, and yet gravity and weight still apply there. So is gravity the acceleration due to the Earth spinning? Or is that something else?

Answer 1

Gravity is a force. Its this that give rise to acceleration of a body so it will fall towards it. Once in contact with it it will not accelerate as it is in contact, but the force exerted on the body will be pushed back by the body it is in contact with. The rate of acceleration is independent on the mass it is acting on so objects accelerate at the same speed when they fall, however the force due to gravity is proportional to the mass.

The earth spinning has nothing to do with the force, if you fall to earth from a fixed position the earth will continue to spin, but you will fall in a straight line. The centrifugal force acted on us when we are on earth is no sufficient to throw us off of the earth either.

Answer 2

Gravitation or gravity is the tendency of bodies having a mass to accelerate towards each other. You can look at it as a force or as an acceleration. When you multiply the acceleration by the mass on which it acts then you get the force.

The fact that there is a force pulling you towards the gravitational centre of the Earth doesn't have anything to do with the Earth spinning. It's only got something to do with the fact that both you and the Earth have mass. And because the mass of the Earth is so much greater than yours (luckily!) it affects you very much more than the other way round. However, even though it is an infinitesimal small amount, but your mass also does affect the Earth, it's only just so small that it's not measurable.

If the Earth wouldn't spin then you would have nearly the same weight as you have now. The spinning motion actual REDUCES the attracting force by gravitation (through a centrifugal force! Sorry but it's exactly the other way round than you described in your question). This means that at the equator you are a little bit lighter than at the poles. But it's just a small amount, so don't worry.

I hope that helps.

Answer 3

Gravity is a force. It is a function of the mass of an object(the greater the mass, the greater the gravitational force.) The strength of the force diminishes according to the distance from the object, so two identical objects would exert different gravitational force depending on their distance, the further away the weaker.

When an object "falls" under the influence of gravity, it accelerates towards the object. We usually are referring to a relatively small object and a relatively large one, IE an apple falling towards the ground. When it hits the ground, of course, it stops accelerating, but gravity is still exerting its influence on it. As it does on us when we are standing on the ground. If it were possible to remove the ground from under our feet, we would indeed continue our journey towards the centre of the earth.

The gravitational pull at the poles is in fact slightly stronger than it is at the equator. This is due to the equatorial bulge, and the flattening at the poles, which means you are closer to the centre of the earth when you stand at the poles than you are at the equator, and the gravitational force is therefore stronger. This is why you generally get better performances and more new records at the Olympic Games when they are held closer to the equator.

The gravitational force is NOT caused by the spin of the earth. The movements of the planets are due to the effects of the original momentum of the matter from which they were made, though this has been affected over time, often due to gravitational effects. For instance, the rotation of the earth has slowed down over time due to the gravitational effect of the moon.

Answer 4

Don't get mixed up between Gravity and Weight. Weight is the force, and it's magnitude is related to the Mass it is associated with. Gravity is the association between Mass and Weight. The value usually called 'g' is the "Acceleration due to Gravity", so gravity is not acceleration or force but something that causes both.
The rotation of the earth is a red herring in this instance. Gravity IS the centripetal force which keeps us accelerating towards the centre of the earth but is not CAUSED by the rotation - it just stops us flying off tangentially.

Answer 5

Gravity is a force of attraction between pieces of matter. Two pieces of matter attract each other with an equal and opposite force. This gravitational force of attraction F is proportional to the product the two masses (M x m) and inversely proportional to the square of the distance between the centres of each mass (r^2). Hence F= G (M x m)/r^2. G is the universal gravitational constant and will be the same anywhere on Earth, the moon, Mars etc. The force of gravitational attraction acting on a mass (m) that is free to move will cause that mass to accelerate (a) in the direction of the force. Hence generally F = ma, and when F is the gravitational force of attraction then a = g where g is the acceleration due to gravity which will vary, of course, depending on M, m and r.

Answer 6

Before you can have a Force, there must be mass and acceleration. As you rightly said, the rotation of the earth creates the accelration that acts on our mass to create gravity. Therefore, gravity is definitely a force. At the geometric poles i believe there is still some force due to the rotation of the earth.

Answer 7

Gravity is a physical force that the masses of 2 or more bodies exert upon each other. Greater masses cause greater forces.

When gravitational forces act upon bodies, those forces attempt to cause the bodies to move. For this motion to take place, acceleration must be greater than 0.

It is this force that keeps us on earth, even at the poles. The rotation of the earth, even on the equator, does not generate enough forces to launch off the surface of the earth.

Answer 8

Isaac Newton discovered that gravity is a force that acts at a distance and attracts bodies of matter toward each other. The force of gravity from the Earth on an object is the acceleration of gravity times the mass of the object. That equals the object's weight. The law of gravity determines how fast objects will fall.

Answer 9

Gravity is only related to mass. It is a force. The Earth exerts the force of gravity on any object, moving or still. If the object is moving it experiences acceleration. Gravity has nothing to do with the spinning of the Earth. Hope that helps.

Answer 10

Gravity is a force, but a rather special one.

It has two properties that are unlike the other forces of nature. Firstly, it acts equally on everything - including things like photons.

Secondly, its magnitude depends on the mass of the object being acted on (in simplistic terms - actually its mass energy). And the force required to accelerate an object also depends on its mass.

The equivalence of these two masses is not obvious, and at the time of Newton two mass values were identified - gravitational mass and inertial mass. Einstein realised that their equivlance is profoundly important, and came up with the principle of equivlance that is at the heart of general relativity. This says that gravity is indistinguishable from acceleration.

So in a way gravity is both.