### Slopes - Forces

These slope questions involve forces. You are generally required to draw a force and / or free body diagrams of the forces involved.

This diagram is usually the starting point.

Given - Draw the force diagram for the 5kg mass, showing the components of it's weight.

Here is the diagram.

F// is the component of the weight that acts downwards, and parallel to the slope. This is the force that accelerates the mass down the slope.

S is the force exerted by the mass perpendicularly onto the slope. (force of mass on slope)

So what do we do with these two forces?
Study this diagram.

F//
F// is copied onto the mass itself, and the acceleration can be calculated:

S
The reaction force to S is the force exerted by the slope on the mass called FN = 42,44N.
• FN is the NORMAL Force.
• A NORMAL Force is the perpendicular force exerted on an object, by the surface on which it is placed.
• Copy S the other way - this would be the force of slope on mass : FN
• S and FN are Newton 3 action-reaction forces.

WITH FRICTION
Lets assume that the above question included a friction force of 10N.

Calculate the magnitude of the acceleration.

Calculate the coefficient of kinetic friction (μ).
This is where the normal force FN is required.

This equation is learnt in Grade 11.You need to know this for your finals.