| English | Inclined plane |
|---|---|
| Bahasa Melayu | Satah condong |
| 中文 | 斜面 |
Definition
A flat surface set at an angle to the horizontal, on which an object's weight can be resolved into components along and perpendicular to the surface.
In exam terms
An inclined plane is a flat surface set at an angle θ to the horizontal. On it, the weight of an object is resolved into two components: one acting down the slope, mg sin θ, and one pressing into the slope, mg cos θ.
The component down the slope tends to make the object slide, while the perpendicular component sets the normal reaction and hence the friction available.
For example, a 2 kg block on a slope of 30° has a weight of mg = 2 kg × 9.81 m s⁻² = 19.6 N. The component pulling it down the slope is 19.6 N × sin 30° = 9.81 N, and the component pressing into the surface is 19.6 N × cos 30° = 17.0 N.
Don't confuse the two weight components
The common trap on an inclined plane is swapping the two weight components. The part along the slope uses sin θ and the part perpendicular to the slope uses cos θ; a quick check is that at θ = 0° (flat ground) the perpendicular part equals the full weight.
Do not confuse the normal reaction with weight either, on a slope the normal reaction equals mg cos θ, which is less than mg.
In Paper 2 this is usually asked with 'Resolve…', 'Calculate the acceleration…' or 'Determine the normal reaction…'. Keep newtons (N) on every line and state the angle you used.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)