# B What does y-intercept of a (a vs F) graph represent?

1. Jul 3, 2017

### efake

Hey! I was creating a force vs acceleration graph. acceleration is on the x axis and force is on the y-axis. I got the slope and it was equal to the mass of the object. However, I got a y-intercept equal to +7.74(positive). What does this represent. Is this the friction or...?

2. Jul 3, 2017

### scottdave

Let's think about this. So in a situation where an object is at rest on a surface with friction, you do apply a force, and nothing happens. Then you apply just the right amount of force to overcome static friction, so the object is now subject to kinetic friction.

So in static situation, the friction force is exactly equal to the applied force, and the object does not accelerate. In kinetic friction, the frictional force will be a constant {equal to mu*(normal force)}, but the slope (change in applied force divided by change in acceleration) would be equivalent to the mass of the object.

But there are other situations, where you apply a small force which causes nothing to happen. Think about a weight sitting on the ground, which you wish to pick up.
What happens when your force is less than the weight of the object? Then when your force is greater, what is happening?

3. Jul 15, 2017

### hackhard

no it was not equal to the mass. you have plotted only 1 force vs acceleration. If you had plotted net external force , then slope would be equal to mass.