What is Free Fall?
Free fall is motion under gravity alone, with no air resistance or other forces. Every object in free fall near Earth's surface accelerates downward at the same rate, regardless of its mass.
Free fall is the motion of an object falling only under gravity, accelerating at g ≈ 9.8 m/s². Velocity grows as v = g·t and distance fallen is h = ½g·t².
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Step-by-step worked examples
An object is dropped and falls for 3 s. Find the distance fallen and its final velocity (g = 9.8 m/s²).
h = ½g·t² = 0.5 × 9.8 × 3² = 0.5 × 9.8 × 9 = 44.1 m v = g·t = 9.8 × 3 = 29.4 m/s
An object falls from rest for 5 s. Find its velocity.
v = g·t v = 9.8 × 5 v = 49 m/s
An object falls 20 m from rest. Find the time it takes.
h = ½g·t² → t = √(2h/g) t = √(2 × 20 / 9.8) t = √4.08 t ≈ 2.02 s
Flashcards
Quick quiz
Q1.An object falls from rest for 4 s. What is its velocity (g = 9.8 m/s²)?
Q2.A feather and a hammer are dropped together in a vacuum. Which lands first?
Q3.An object falls from rest for 2 s. How far has it fallen (g = 9.8 m/s²)?
Q4.What force(s) act on an object in true free fall?
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Common mistakes
Believing heavier objects fall faster in free fall. — Correct: In a vacuum, all objects fall at the same acceleration g, regardless of mass.
Ignoring air resistance and calling any falling object 'free fall'. — Correct: True free fall requires no air resistance — with air resistance, motion isn't pure free fall.
Using v = g·t even when the object has an initial velocity. — Correct: If there's an initial velocity v₀, use v = v₀ + g·t instead.
Mixing up the formulas for velocity and distance. — Correct: Velocity is linear in time (v = g·t); distance is quadratic in time (h = ½g·t²).
FAQ
What is free fall?
Free fall is the motion of an object falling under gravity alone, with acceleration g ≈ 9.8 m/s² and no other forces.
What is the formula for free fall?
Velocity: v = g·t. Distance fallen: h = ½g·t², both starting from rest.
How do you calculate free fall with an example?
For t = 4 s: v = 9.8 × 4 = 39.2 m/s and h = 0.5 × 9.8 × 16 = 78.4 m.
Does air resistance affect free fall?
Yes — true free fall assumes no air resistance. In real air, lighter or larger objects fall slower due to drag.