IGCSE 0625 / Section 1.2 / Core

Falling at a steady rate.

Drop a heavy hammer and a light feather together, with no air in the way, and they land at the same instant. Near the Earth surface every object gains speed at the same fixed rate regardless of mass. That rate has a name and a syllabus value: g, about 9.8 metres per second, every second.

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The key idea

Near the Earth surface, and strictly ignoring air resistance, all objects fall with the same constant acceleration g = 9.8 m/s². The acceleration does not change as the object falls; the velocity does.

Section 01

Equal gains, every second.

Release the objects and watch the strobe marks, one for each second. The gaps grow larger because they are speeding up. Toggle the air resistance on and off to see the rule: constant acceleration applies to all masses only in a vacuum.

Stage 1 · Learn

Check what free fall really means

Four quick checks on g and constant acceleration. Each correct answer earns XP and lights this skill on your star map.

Quick check+10 XP

Ignoring air resistance, a heavy hammer and a light feather dropped together will...

Quick check+10 XP

The acceleration of free fall near the ground is about...

Quick check+10 XP

As an object falls freely with no air resistance, its acceleration...

Quick check+10 XP

All objects fall with the same acceleration because g does not depend on...

Section 02

What stays the same, and what grows.

Same for all masses: ignoring air resistance, a hammer and a feather fall together, because g does not depend on mass.
Acceleration is constant: g stays at about 9.8 m/s² throughout the fall in a vacuum.
Velocity grows steadily: the speed increases by about 9.8 m/s during every second, so for a drop from rest v = g t.

The velocity-time graph for free fall is a straight line through the origin: a constant gradient means a constant acceleration.

Examiner trap

A common belief is that a falling object accelerates more and more as it drops. Ignoring air resistance, this is wrong. The acceleration stays fixed at about 9.8 m/s². What increases is the velocity, at a steady rate. The growing gaps in a strobe photo show rising speed, not rising acceleration.

Worked example

A stone is dropped from rest. Taking g = 9.8 m/s² and ignoring air resistance, find its velocity after 3.0 s, and state its acceleration at that moment.

Step 1 · Velocity from v = g tv = g t = 9.8 × 3.0 = 29.4 m/s

Step 2 · AccelerationThe acceleration is still 9.8 m/s². It has not changed; only the velocity has grown.

Step 3 · Answervelocity = 29 m/s downward; acceleration = 9.8 m/s², constant throughout.

Stage 2 · Exam

Exam-style questions

Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 1.

Finish the four checks above to unlock the exam questions

Exam style+20 XP

A stone is dropped from rest. Taking g = 9.8 m/s² and ignoring air resistance, its speed after 2.0 s is...

Exam style+20 XP

In a vacuum tube, a coin and a feather released together reach the bottom at the same instant because...

Exam style+20 XP

A strobe photo of a falling ball shows the gaps between images growing larger each second. This shows that the ball is...

Skill unlocked

Acceleration of free fall, mastered.

This skill is now lit gold on your star map. Keep the chain going.

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Go deeper · practice

Six original Cambridge-style questions

The acceleration of free fall, why all masses fall together when air resistance is ignored, calculations using g, and keeping mass and weight distinct. Attempt each, then reveal the worked solution.

Stage 3 · master the unit

Motion, forces and energy challenge

Mixed questions across the whole unit, each one worth XP. Start this only when you feel confident across every topic in the unit, not just free fall.

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