General Physics Fundamentals
Core concepts
This domain rewards dimensional fluency and order-of-magnitude reasoning. Know Newton's laws as statements about net force and momentum change, conservation of energy and momentum, the distinction between scalar speed and vector velocity, and the kinematics equations for constant acceleration. Be comfortable with unit conversions (SI prefixes, eV to joules, degrees to radians) and with the idea that physical laws must be dimensionally consistent.
Traps
- Vector vs. scalar: distance is not displacement; average speed is not the magnitude of average velocity when direction changes.
- Sign conventions: choose an axis and keep it; a dropped object's acceleration is negative if up is positive.
- Mass vs. weight: weight is mg, a force; mass is invariant.
- Frames: centrifugal and Coriolis terms appear only in rotating frames.
- Significant figures and units in numeric answers; a correct number with wrong units is wrong.
Worked example
A ball is thrown straight up at 20 m/s. How high does it rise (g = 10 m/s²)? At the top v = 0, so v² = v₀² − 2gh gives 0 = 400 − 20h, hence h = 20 m. Rule of thumb: at the apex the velocity is zero but the acceleration is still g downward - a favorite conceptual trap.
Rule of thumb
Before computing, check dimensions and limiting cases. If a formula must reduce to a known result when a parameter goes to zero or infinity, test it.