Grade 11 · Theory
Forces on an incline
Vectors in two dimensions · about 3 min
Forces on a block resting on a rough incline.On a slope it is far easier to tilt the axes so one lies along the incline.
Key points- Component of weight down the slope: Fg∥ = mg·sin θ.
- Component perpendicular to the slope: Fg⊥ = mg·cos θ, which equals the normal force FN.
- Friction acts along the surface, opposing motion or its tendency: Ff = μFN.
- The object slides when the component down the slope exceeds maximum static friction.
- Normal force — the surface's perpendicular push.
- Coefficient of friction (μ) — the roughness ratio.
EXAM TIP
on an incline the normal force is NOT mg — it is mg·cos θ, and forgetting this breaks the friction calculation.