# 1.2.4 Freefall

### Freefall: Basics

• In the absence of air resistance, all objects fall with the same acceleration, regardless of their mass
• This acceleration is equal to the gravitational field strength and is approximately 10 m/s2 near the Earth’s surface
• So long as air resistance remains insignificant, the speed of a falling object will increase at a steady rate, getting larger the longer it falls for.

In the absence of air resistance objects fall with constant acceleration

Extended Only

### Terminal Velocity

• When a parachutist jumps out of an aeroplane, two main forces act:
• Weight (the force of gravity)
• Air resistance

Diagram showing how the changing forces on a skydiver

• Initially the air resistance is very small. There is a downwards unbalanced force and the skydiver accelerates
• As the skydiver speeds up, the air resistance increases
• Eventually the air resistance balances the weight and so the skydiver travels at a constant speed – terminal velocity
• When the parachute is opened the increase air resistance on the parachute creates an upwards unbalanced force, making the parachuting the slow down

Graph showing how the velocity of a skydiver changes during the descent

#### Exam Tip

The force of gravity on an object is called weight. If asked to name this force make sure you use this word: Don’t refer to it as “gravity” as this term could also mean gravitational field strength and so would probably be marked wrong.

Likewise, refer to the upward force as air resistance or drag. The terms wind resistance and air pressure mean different things and so would also be marked wrong.

### Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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