The falling ball

The idea

An object dropped from a height falls along a straight vertical path with a constant acceleration of 9.8 m s–2 in its direction of motion, called the acceleration due to gravitational force by the Earth and denoted g.

Let go of a ball

You hold a ball high and let it go. It starts from rest and falls straight down. Its velocity is read at the end of each second.

How do you think the velocity changes as the ball falls?

• It increases by the same amount every second
• It stays the same
• It decreases every second

Drop the ball

Press Drop and watch the velocity.

The same gain every second

At the end of each second the velocity was larger by 9.8 m s⁻¹: 9.8, 19.6, 29.4 and 39.2 m s⁻¹. So the average acceleration in every second was 9.8 m s⁻², in the direction of the motion.

An object dropped from a height falls along a straight vertical path with a constant acceleration of 9.8 m s⁻² in the direction of its motion. It is called the acceleration due to gravitational force by the Earth and is denoted by g.

Notes

A dropped object falls with a constant acceleration g = 9.8 m s⁻², in the direction of motion: the acceleration due to gravity.

Check yourself

An object dropped from a height falls with a constant acceleration of about…

A ball is dropped from rest. What is its velocity after 2 s?

Answer: 19.6 m s⁻¹

9.8 m s⁻² × 2 s = 19.6 m s⁻¹.

What is the direction of the acceleration of a falling object?

What is g?

• 9.8 m s⁻¹. m s⁻¹ is a unit of velocity. Acceleration is measured in m s⁻².
• 0 m s⁻², because it falls along a straight line. Its velocity increases every second, so its acceleration is not zero.
• 9.8 m s⁻² — correct. Yes!
• In the direction of its motion, downwards — correct. Yes!
• Opposite to its motion, upwards. The velocity is increasing in the direction of motion, so the acceleration is in that direction.
• There is no direction, only a value. Acceleration has a direction as well as a magnitude.
• The velocity of a falling object. The velocity of a falling object keeps increasing. g is a constant acceleration.
• The acceleration due to gravitational force by the Earth — correct. Yes!
• The mass of a falling object. g is an acceleration, measured in m s⁻², not a mass.