# does f=ma describe gravity?

or another force?

Update:

i guess what im trying to get at is that if something gets heavier as it goes faster wouldnt gravity be the force which cause objects to pull more mass to themselves?

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• Anonymous
7 years ago

newton's second law

F=ma

in terms of gravity

F=mg where g is acceleration due to gravity

note: g is constant 9.81 on earth's surface

so yes

f=ma describe gravity but a=g for force due to grivty

For example if you dropped a soccer ball of mass .5 kg

the force due to grivty would be

F=mg

F=(.5)(9.81)

F= 4.9 Newton (force of grvity on ball)

hope it hepls

Source(s): college student
• Not necessarily.

F = MA is a very general statement of Newton's Second Law of Motion, which says a mass, M, accelerates, A, when a net force, F, is applied to it. And that's all it says.

No gravity. In fact the source of the force, F, is not specified in F = MA.

There is no reason at all why F cannot be W, the force of gravity, which is often called weight. When you step onto a bathroom scale and read off your weight, you are reading off the force due to gravity. So there is no reason why one cannot write F = W = MA; where A = W/M = g is the acceleration due to the force of gravity, the weight.

F might also come from F = qE + q(v X B) = MA where E and B are the electro magnetic fields and q is some charge that the mass M has. So instead of gravity, this force comes from the electro-magnetic fields acting on a charge.

And force might also come from F = MV^2/R = MA where V is the tangential speed of the mass M going around a circle of radius R. A = V^2/R here is the radial acceleration along the radius R.

Bottom, line, F = MA is just a general relationship. What the source of the force and the mass are depends on the specific problem.

• To answer your question, no, this is not an equation that describes gravity. It is a general equation relating force, mass and acceleration that comes from Newton's second law of motion. This law, in words, says that

'The rate of change of momentum is proportional to the applied force and takes place in the direction in which the force acts'

This law tells us how to measure a force by studying the rate of change of momentum of an object.

So

F proportional to dp/dt

But momentum = mass * velocity = m v

Now, in Newtonian physics, the mass remains constant. So, for the momentum to change, the velocity must change. So

F proportional to m dv/dt

But, dv/dt is the definition of acceleration. So

F proportional to ma.

To turn this into an equation, we must include the constant of proportionality. So

F = k m a

But, if we choose the units carefully, we can make k = 1. So

F = m a

The force equation for gravity, according to Newton, is

F = G M m / r^2

where F = force of gravity (N); G = universal constant; M and m are the masses of the two objects (Kg); r = distance between their centers of mass.

• It describes any force. With gravity, the force is proportional to mass, so the acceleration is constant (on earth, if you ignore friction). With other forces, if the mass increases, acceleration decreases.