Free Fall and Downward Motion
For vertical motion near Earth's surface with negligible drag, acceleration is constant and downward with magnitude g. Choosing upward positive gives a = -g; choosing downward positive gives a = +g.
Why this shows up in the exam
Bodies dropped from towers · Downward throws · Comparing fall times over height intervals
Learn the idea
Near Earth and without air resistance, every freely moving body has the same downward acceleration g. Once released, a body gains equal downward velocity in equal times. Its mass does not enter the ideal kinematics, but the signs depend on which vertical direction is chosen positive.
🧠 Memory hook: Gravity points down; the equation sign follows your axis.
Get this one clearly and it pays off every single time it shows up in the paper. 🎯
Formulas & facts to keep ready
- v = u - gt — vertical velocity with upward chosen positive
- y-y0 = ut - (1/2)gt² — vertical displacement with upward positive
- v² = u² - 2g(y-y0) — time-eliminated vertical relation
How to approach it
- 1Declare upward or downward positive
- 2Translate every height into one coordinate
- 3Apply constant-acceleration equations with consistent signs
Common slip-ups that cost marks
- •Changing the sign of g halfway through
- •Setting initial velocity to zero for a downward throw
- •Using distance as signed vertical displacement
🌟 That's the whole idea — you've got this. Try the practice set below; every question you attempt makes it stick a little harder.
Original chapter practice
Original questions for this chapter, not past-paper questions or an exact mapping to this individual concept.
A particle has initial speed 2 m/s and constant acceleration 3 m/s^2 for 4 s. What distance does it cover?
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