Pearson Edexcel · GCSE · Physics
Course version: 1PH0 · Version from Sept 2016
Recall that the acceleration, g, in free fall is 10 m/s² and be able to…
Full specification wording
Topic 2 – Motion and forces: 2.13 Recall that the acceleration, g, in free fall is 10 m/s² and be able to estimate the magnitudes of everyday accelerations
Near the Earth's surface, an object falling freely (with only its weight acting, air resistance negligible) accelerates downward at about 10 m/s².
Checked against the Pearson Edexcel 1PH0 specification (opens in a new tab) on .
- Point 13 of 32
Study notes
From the checked teaching notes for this specification point.
The idea
Near the Earth's surface, an object falling freely (with only its weight acting, air resistance negligible) accelerates downward at about 10 m/s². That means its velocity changes by roughly 10 m/s every second: released from rest, it reaches about 10 m/s after 1 s, 20 m/s after 2 s and 30 m/s after 3 s. Use g = 10 m/s² in calculations such as v = u + at and s = ut + ½at². You must also estimate everyday accelerations by comparing velocity changes with the time taken: a car going from 0 to 20 m/s in 4 s has a = 20 ÷ 4 = 5 m/s²; a bus braking from 15 m/s to rest in 5 s has a = 15 ÷ 5 = 3 m/s² (deceleration). Free-fall acceleration, about 10 m/s², is far larger than most everyday road accelerations of a few m/s².
What earns the marks
- States that the acceleration of free fall near the Earth's surface is about 10 m/s².
- Applies g = 10 m/s² in a kinematics calculation such as v = u + at or s = ut + ½at².
- Calculates an everyday acceleration by dividing the change in velocity by the time taken.
- Estimates the magnitude of an everyday acceleration and compares it with the free-fall value of about 10 m/s².
Common mistakes and how to put them right
Uses g = 9.8 m/s² or another value when the question expects the recalled value of 10 m/s².
Put it right: Use 10 m/s² as specified.
Divides the final velocity by the time without subtracting the initial velocity.
Put it right: Use the change in velocity, final minus initial.
Treats a deceleration as a negative magnitude when asked for the magnitude.
Put it right: Give the size as a positive value and state the direction or that it is slowing.
Assumes a falling object keeps accelerating at 10 m/s² forever regardless of air resistance.
Put it right: Recognise that the estimate applies to free fall with negligible air resistance.
Exam tips
- Write the recalled value as 10 m/s² with correct units before substituting into any equation.
- For estimation questions, show the change in velocity and the time, then divide, so the method is visible.
- Sanity-check an everyday acceleration against about 10 m/s²: road vehicles usually give a few m/s², not tens.
- Keep the squared unit m/s² throughout; do not drop the exponent.
Try the lesson
The start of the Topic 2 – Motion and forces: 2.13 Recall that the acceleration, g, in free fall is 10 m/s² and be able to estimate the magnitudes of everyday accelerations lesson, made from checked teaching notes for this specification point.
Have a go first
Which value best estimates the acceleration of an object in free fall near the Earth's surface?
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