GCSE · Physics · Edexcel · Spec 1PH0

Acceleration of free fall g = 10 m/s^2

Let go of a ball and it gains speed at a perfectly steady rate: 10 m/s after one second, 20 m/s after two. That rate has a name — g.

A ball dropped from rest, falling freely

Time since it was let go (s): 2.5. Velocity (m/s): 25

Drag the dot along the line and stop on each whole second: 1, 2, 3, 4, 5.

What 'falling freely' means

Tap the arrow. Notice there's only one.

Tap a force to see what it does.

What do you think?

Heavy ball, light ball

A bowling ball and a tennis ball are let go at the same moment, from the same height. Air resistance is negligible for both, so both are in free fall.

Which is closest to what you think right now?

The bowling ball speeds up faster, because it's much heavier.The tennis ball speeds up faster, because it's lighter and easier to get moving.They speed up at exactly the same rate, so they stay side by side.

How sure are you?

I'm sureI think soI'm guessing

The bowling ball speeds up faster, because it's much heavier.

This is a common misconception

This is the most common idea there is — and it's wrong. With air resistance negligible, every object in free fall has the same acceleration, g = 10 m/s². The bowling ball's extra mass doesn't give it a bigger acceleration: both balls gain 10 m/s every second.

The tennis ball speeds up faster, because it's lighter and easier to get moving.

This is a common misconception

Tempting, but no. Being lighter doesn't earn the tennis ball a bigger acceleration. In free fall both balls accelerate at g = 10 m/s², so both gain 10 m/s every second.

They speed up at exactly the same rate, so they stay side by side.

This matches the evidence

Yes. With air resistance negligible, both accelerate at g = 10 m/s², whatever their mass. They start together from rest and gain the same 10 m/s every second, so they stay side by side all the way down and land together.

Mass makes no difference in free fall: with air resistance negligible, every falling object accelerates at g = 10 m/s².

Using g in a calculation: working backwards

Problem

A stone is dropped from rest off a high bridge and falls freely (air resistance negligible). How long does it take to reach a velocity of 25 m/s?

Spot the slip

Where does this answer go wrong?

A coin is dropped from rest and falls freely for 3 s (air resistance negligible). What is its velocity after 3 s?

A student's answer — which line goes wrong?

It starts from rest, so its starting velocity is 0 m/s.
It's falling freely, so its acceleration is g = 10 m/s².
The unit is m/s², so I square the time: change in velocity = 10 × 3² = 90 m/s.
Velocity after 3 s = 0 + 90 = 90 m/s.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

What you need to know

What 'falling freely' means in terms of the forces acting
What the value g = 10 m/s² tells you about a falling object's velocity
Why mass makes no difference to the acceleration in free fall
How to use g = 10 m/s² as the acceleration in a velocity or time calculation

The big picture

An object in free fall has only its weight acting on it. Near the Earth's surface it accelerates at g = 10 m/s², so its velocity rises by 10 m/s every second — and that's the same for heavy and light objects when air resistance is negligible.

Key points

1Free fall means the object's weight is the only force acting on it — air resistance is negligible.

2Near the Earth's surface, an object in free fall accelerates at g = 10 m/s².

310 m/s² means the velocity goes up by 10 m/s every second: 0, 10, 20, 30 m/s and so on.

4With air resistance negligible, all objects in free fall have the same acceleration, whatever their mass.

5In calculations, use g = 10 m/s² as the acceleration in acceleration = change in velocity ÷ time.

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Worked example

Problem

A ball falling freely is already moving downwards at 8 m/s. How fast is it moving 1.5 s later? (Air resistance is negligible.)

⚠ Watch out

Mixing up acceleration with velocity or distance. g = 10 m/s² does not mean the object falls at a steady 10 m/s, and it does not mean it drops 10 m each second. It means its velocity goes up by another 10 m/s every second.

🧠

Memory hook

Say it out loud: 'ten metres per second, every second'. Then count the speed up in tens — 0, 10, 20, 30 — one ten for every second it falls.

✓

Check yourself

Without looking back: a pebble is dropped from rest and falls freely. How fast is it moving after 3.5 s — and would a heavier pebble be moving any faster?

Flashcards

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What does 'free fall' mean?

Falling with weight as the only force acting — air resistance is negligible.

What is the acceleration of an object in free fall near the Earth's surface?

g = 10 m/s².

Put 10 m/s² into words.

10 metres per second, every second: the velocity goes up by 10 m/s each second.

Does a heavier object have a bigger acceleration in free fall?

No. With air resistance negligible, every object in free fall accelerates at g, whatever its mass.

Which relationship lets you use g in a motion calculation?

Acceleration = change in velocity ÷ time, with g = 10 m/s² as the acceleration. Rearrange it for the time or the change in velocity.

Finding the velocity after 3 s of free fall from rest: is it 10 × 3 or 10 × 3²?

10 × 3 = 30 m/s. The ² in m/s² means 'per second, per second' — it isn't telling you to square the time.

What does the velocity–time graph of an object falling freely from rest look like?

A straight line from the origin, climbing by 10 m/s for every second.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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A ball dropped from rest, falling freely

Heavy ball, light ball

Where does this answer go wrong?

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