# F = ma, but why mass isn't dependent on force?

### 12 Answers

- goringLv 67 months ago
Force does not exist by itself. The Newton equation of gravity Force is composed as follows;

Force = Fo x F' x(1/Fu).

Where Fo & F' are structural force of of the interacting masses and Fu is a structural force that is universal.

Thus all masses have a gravitational structural force.

When two masses collide two forces are born. That means there is a collusion yielding forces that are equal and opposite in direction.

Hence forces are born in pairs

Note; there are four forces in Newton gravity equation where as Einstein gravity equation only indicates the ratio of two forces

- Goldy AluminyLv 57 months ago
Perhaps you are confusing mass and weight. Mass is a measure of amount of "stuff" there is, which is expressed in grams. Weight is a measure of the force a mass exerts in the presence of gravity or acceleration and is expressed in grams. You can think of gravity as an accelerating force.

In other words, just because there is no gravity, does not mean that objects don't have a mass. They might be weightless, but not massless (Conservation of mass concept).

- Jeffrey KLv 67 months ago
Newton's true equation is F =dP/dt This means force equals the rate of change of momentum. Momentum P = mv If we assume mass is constant, the formula becomes F = ma. This assumption that mass is constant is true in most common situations. But not always.

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- Andrew SmithLv 77 months ago
The fact that two things are related has nothing to do with a physical dependence.

The dependence in the formula as written is that the FORCE is dependent on the product of the provided mass and acceleration.

If you rewrite it to m = F/a then you imply a dependence but the wording becomes "the mass REQUIRED is equal to the quotient Force divided by acceleration"

It does not magically create mass.

In other words mathematics can express many things. What it cannot do is to express the real world and the entire problem. It is up to YOU to provide the interpretation ( if any exists) for the equation you create.

- Old Science GuyLv 77 months ago
...

the equation is more properly

a = F / m

where a is the dependent variable

and F and m are independent variables

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- busterwasmycatLv 77 months ago
normally, we chose the object first. mass is dependent on the object. There are situations where the mass "depends" on the force, in the sense that you cannot have a specific acceleration without a particular mass for a force.

But normally, the issue is one of perspective. We are concerned with an object, and that object is what it is, including its particular mass.

- VamanLv 77 months ago
Actually mass can depend on the force, Actual equation is d/dt p=force. p is the momentum, Your equation is valid only when m is a constant.

Thermodynamics is not a part of classical mechanics. Thermodynamics can be studied with the help of statistical mechanics. The mechanics we study is the exact one and normally the energy losses are ignored.

- LucaLv 67 months ago
1) That formula is only an approximations, it only works with things that aren't too fast, or too small (or both).

2) Cause it doesn't. Not much we can say, Nature behaves like this: we find that there's a linear relation between the force applied on a body and its acceleration, we call the proportionality constant "mass" and, by definition, the mass define the inertia of an object (that is, its resistance to acceleration when pushed by a force).

3) There are some certain scenario in physics in which mass isn't constant or it's not a scalar and it can behave weirdly. In particular in certain crystals, electrons and holes move AS IF they had an "effective mass" that is different from their usual mass. This effective mass can be negative (the electron moves backward when pushed forward), can change with the parameter of the crystal and can be a tensor (a matrix, so that the effect of the force depends on the direction of application), thus creating some really strange phenomena.

4) In relativity some people will say that mass changes with speed and so we can somehow say that m depends on the force, but the "mass changes with speed" thing is really old and not used anymore, it's not a really useful concept and it does create a lot of confusion with little gain. Nowdays with mass in relativity people mean "rest mass" and this is constant (in closed systems) and invariant (so all observers agree on the value of the rest mass).

(A good example of changing mass in the calculation is rockets which propel themselves forward by throwing mass backwards)