OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Physics on the move: estimate the magnitudes of everyday accelerations
Here you judge how quickly velocity changes in familiar situations, using acceleration = change in velocity ÷ time.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 2 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Here you judge how quickly velocity changes in familiar situations, using acceleration = change in velocity ÷ time. A car going from rest to about 30 m/s in 10 s has an acceleration near 3 m/s². A bus pulling away gently is around 1 m/s²; hard braking can reach about 8–10 m/s². A dropped object accelerates at about 10 m/s² due to gravity. A train easing out of a station is small, perhaps 0.5 m/s². Use the formula to check an option: divide the velocity change by the time taken. Values far above 10 m/s² for ordinary road travel are unrealistic, and a negative value simply means slowing down.
What earns the marks
- Applies acceleration = change in velocity ÷ time to test a proposed value.
- Estimates a car accelerating from rest to about 30 m/s in 10 s as roughly 3 m/s².
- Recognises free fall near the Earth's surface as about 10 m/s².
- Assigns gentle public-transport acceleration a value near or below 1 m/s².
- Interprets a negative acceleration as deceleration during braking.
- Rejects an everyday road acceleration far greater than 10 m/s².
Common mistakes and how to put them right
Divides time by velocity change.
Put it right: Divide the velocity change by the time instead.
Gives a braking car a positive acceleration while calling it slowing.
Put it right: Treat slowing as negative acceleration.
Estimates free fall as far from 10 m/s².
Put it right: Keep it near 10 m/s².
Assigns a bus the same acceleration as a hard-braking car.
Put it right: Keep gentle starts near 1 m/s².
Exam tips
- Substitute the velocity change and time into the formula before choosing an option.
- Sanity-check the answer against the 10 m/s² free-fall benchmark.
- Watch the sign: deceleration is a negative acceleration.
Try the lesson
The start of the Physics on the move: estimate the magnitudes of everyday accelerations lesson, made from checked teaching notes for this specification point.
Have a go first
Which value is the best estimate for the acceleration of a car pulling away gently from traffic lights?
Listen
Here you judge how quickly velocity changes in familiar situations, using acceleration = change in velocity ÷ time. A car going from rest to about 30 m/s in 10 s has an acceleration near 3 m/s². A bus pulling away gently is around 1 m/s²; hard braking can reach about 8–10 m/s². A dropped object accelerates at about 10 m/s² due to gravity. A train easing out of a station is small, perhaps 0.5 m/s². Use the formula to check an option: divide the velocity change by the time taken. Values far above 10 m/s² for ordinary road travel are unrealistic, and a negative value simply means slowing down. A strong answer earns marks for these points. Applies acceleration = change in velocity ÷ time to test a proposed value. Estimates a car accelerating from rest to about 30 m/s in 10 s as roughly 3 m/s². Recognises free fall near the Earth's surface as about 10 m/s². Assigns gentle public-transport acceleration a value near or below 1 m/s². Exam tip: Substitute the velocity change and time into the formula before choosing an option.
Key words
Say what each word means before you turn the card.
Acceleration as rate of change of velocity
Try answering aloud or in your head before turning the card.
Free-fall acceleration
Try answering aloud or in your head before turning the card.
Deceleration and sign
Try answering aloud or in your head before turning the card.
Order-of-magnitude estimation
Try answering aloud or in your head before turning the card.
See every definition
- Acceleration as rate of change of velocity
- Judged by dividing the change in velocity by the time taken, using acceleration = change in velocity ÷ time.
- Free-fall acceleration
- A dropped object accelerates at about 10 m/s² due to gravity, and this is the benchmark for sanity-checking answers.
- Deceleration and sign
- A negative value simply means slowing down, so braking is treated as negative acceleration.
- Order-of-magnitude estimation
- Values far above 10 m/s² for ordinary road travel are unrealistic, while gentle public transport is near or below 1 m/s².
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Physics on the move: estimate the magnitudes of everyday accelerations
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge