# Force, momentum equation

1. May 17, 2015

### TT0

Hello,

In the equation ∆p = F∆t, what does F stand for. I know it stands for force but what type of force? For example is it the force of the collision or the force if the object hits something etc.

Thanks

2. May 17, 2015

### HallsofIvy

It is any type of force at all. That equation says that if a force, F, whether a collision force, magnetic force, gravitational force, etc., acts on any object for a time interval of length $\Delta t$, that force will change the objects momentum by $\Delta p= F\Delta t$.

3. May 17, 2015

### Staff: Mentor

The only restriction on F in that equation is that it must be constant over the time interval. There is a calculus-based version of the same formula which can be used for non-constant forces.

4. May 17, 2015

### HallsofIvy

Right, thanks. I was thinking of $\Delta p$ and $\Delta t$ as 'infinitesmals'.

Last edited by a moderator: May 17, 2015
5. May 17, 2015

### PeroK

In fact, that's one way to define a force: something that causes a change of momentum. Anything that causes a change of momentum is then, by definition, a force.

6. May 17, 2015

### TT0

All right, thanks everyone it has been very helpful!