Physics Content: Motion, Forces, Waves and Circuits
What you must understand
This domain is the quantitative core. For motion, use displacement, velocity and acceleration with equations such as v = u + at and s = ut + ½at², and interpret motion graphs (gradient of displacement-time = velocity; gradient of velocity-time = acceleration; area under velocity-time = displacement). For forces, apply Newton's laws, resolve vectors, and analyse friction, tension, normal force and circular motion (centripetal force directed to the centre).
For energy and momentum, use work, power, efficiency and conservation. For waves, know frequency, wavelength, speed (v = fλ), reflection, refraction, diffraction, superposition, standing waves and the electromagnetic spectrum. For circuits, apply Ohm's law, series and parallel rules, and power relationships.
Traps
- Mixing up displacement and distance, or speed and velocity.
- Forgetting that acceleration due to gravity acts downward throughout projectile motion, including at the top.
- Using degrees where radians are needed, or forgetting to convert units (cm to m).
- Treating wave speed as changing with frequency through the same medium; in a given medium, speed is fixed and frequency changes with source.
- Reversing series and parallel resistance rules.
Worked example
A ball is thrown horizontally at 8.0 m/s from a 20 m cliff. Vertical: 20 = ½ × 9.8 × t², so t ≈ 2.02 s. Horizontal range = 8.0 × 2.02 ≈ 16 m. The horizontal velocity stays 8.0 m/s; the vertical velocity at impact is 9.8 × 2.02 ≈ 19.8 m/s downward. Combine with Pythagoras for the final speed.