Free Fall
Simple Explanation
Free fall is motion under gravity alone, with no other forces (like air resistance) acting. Near Earth's surface, every falling object accelerates at approximately 9.8 m/s², regardless of its mass — this is called the acceleration due to gravity, g.
Why Do We Need It?
Free fall is a real, everyday example of constant (uniform) acceleration, which means all four equations of motion apply directly to it — just substitute g for a.
Worked Example
Find how far a dropped ball falls
A ball is dropped from rest and falls for 2 s. Using g = 9.8 m/s², find how far it falls.
Why Does This Work?
Because gravity provides a constant acceleration near Earth's surface, free fall is just a special case of the same uniform-acceleration motion described by all four equations — with a replaced by g.
Real-Life Example
Skydiving before the parachute opens
In the first few seconds of a skydive, before air resistance becomes significant, a skydiver accelerates at very close to g.
The same equations of motion used for any accelerating object correctly predict a skydiver's speed and fall distance during this initial phase.
Practice
An object is dropped from rest and falls for 3 s. Using g = 9.8 m/s², find its velocity after 3 s.
MediumCommon mistake
Assuming heavier objects fall faster than lighter ones — in free fall (ignoring air resistance), all objects accelerate at the same rate, g, regardless of mass.
Quick Review
- Free fall = motion under gravity alone.
- g ≈ 9.8 m/s² near Earth's surface, for every object.
- All four equations of motion apply to free fall — just substitute g for a.