Not given in the exam, recall it.
What it is for
Vertical component of a force is used in Force and Motion II (SPM Physics Form 5). Keep the SI units in every line of working. Force and Motion II
Symbols and SI units
| Symbol | Meaning | SI unit |
|---|---|---|
| F_y | vertical component of force | N |
| F | force | N |
| θ | angle to the horizontal | ° |
Rearrangements
F = F_y / sin θsin θ = F_y / F
Worked example
Common trap
Understanding the vertical component of a force
The formula F_y = F sin θ resolves a force into its vertical part. F_y is the vertical component in newtons (N). F is the full force, also in newtons. θ is the angle to the horizontal, in degrees (°).
Sine appears because the vertical side is opposite the angle. As θ increases, sin θ increases, so more of the force acts vertically, a force pointing steeply upward lifts strongly but drags forward only weakly.
Rearrange when needed: F = F_y / sin θ recovers the full force, and sin θ = F_y / F gives the angle. Keep the calculator in degree mode and measure θ from the horizontal, so that a large angle correctly produces a large vertical component.
A worked example, step by step
A cable pulls a load with force F = 200 N at θ = 25° to the horizontal. Find the vertical component that helps lift the load.
Apply the formula with units:
- F_y = F sin θ = 200 N × sin 25°
- F_y = 200 N × 0.423 = 84.5 N
So the upward part of the pull is F_y = 84.5 N (3 significant figures). This is the share that reduces the load's effective weight on the ground.
Check: because 25° is a shallow angle, sin 25° is small, so F_y (84.5 N) is much less than F (200 N). Most of the force here acts horizontally, which matches the small angle.
Common mistakes and how this is tested
The main trap: use sin for the component opposite the angle (usually vertical), and measure θ from the horizontal.
Other common errors:
- Swapping sin and cos, giving the horizontal component instead.
- Forgetting that weight (mg) may add to or oppose F_y in equilibrium problems.
- Using radian mode, so sin 25° is wrong.
Questions ask you to calculate the vertical component, to define the resolution of a force into perpendicular components, or to explain how the vertical component affects the normal reaction or apparent weight.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)