# Force, mass and acceleration constrained

Increase the force to get a bigger acceleration: increase the mass to get a smaller acceleration. See how force and mass constrain acceleration here.

You can compare the motion of two separate things, setting the mass and acceleration for each.

This constraining is an all-at-once connection. It's not first one thing, then another.

Not everything is possible either: some possibilities are ruled out. One way to explore possibilities is to sketch them on a graph. Fix the mass, and then vary the force to see how the force and the acceleration are related.

You can also fix the force, and then vary the mass to see how the force and the acceleration are related.

Constraint relationships, like this one, limit possibilities. You know a little about the world(it's more predictable) because you know some situations are just impossible. Summarise all of this learning in a mathematical relationship between the acceleration (*a*, the force(*F*), and the mass *m*.

*F**m* = *a*

### A constraint relationship, animated

You can see this relationship animated, like this:

### Constrained vs unconstrained

This idea of a constraint relationship

is important. Lots of the knowledge that physics has about the world is like this. So here is what does happen.

And here is what physicists have learnt does not happen.

Our lived-in world is well described by:

*F**m* = *a*