Forces, motion and momentum
Newton's laws connect forces to changes in motion. Most exam questions are an application of one of the three.
Lesson overview
What you'll learn in this lesson
Apply the laws of motion and wave behaviour to explain and calculate.
Key learning points
- • Newton's laws
- • Motion graphs
- • Stopping distance and momentum
This lesson at a glance
- 30 minutes
- 19 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 19
Visual introductionPicture this
Forces, motion and momentum
Newton's laws connect forces to changes in motion. Most exam questions are an application of one of the three.
In a nutshell
Apply the laws of motion and wave behaviour to explain and calculate.
Learning cycle
Part 2 of 19
Learning cycle 1 of 2
Part 1 · Newton's laws
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 3 of 19
Learn
Newton's laws
First: an object stays at rest or at constant velocity unless a resultant force acts. Second: F = ma, so the same force gives a smaller acceleration to a larger mass. Third: every action has an equal and opposite reaction, and the pair always acts on two different objects.
Reset break
Part 4 of 19
Pause
That's sitting 1 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 5 of 19
Learn
Motion graphs
On a distance–time graph the gradient is speed; on a velocity–time graph the gradient is acceleration and the area under the line is the distance travelled. A curved distance–time graph shows acceleration. Being asked for 'the distance' from a velocity–time graph means finding an area.
Quick check
Part 6 of 19
Quick check
Part 7 of 19
Reset break
Part 8 of 19
Pause
That's sitting 2 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 9 of 19
Learning cycle 2 of 2
Part 2 · Stopping distance and momentum
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 10 of 19
Learn
Stopping distance and momentum
Stopping distance is thinking distance plus braking distance. Tiredness, alcohol and distraction increase thinking distance; speed, road conditions and worn brakes increase braking distance. Momentum p = mv is conserved in collisions, and safety features such as crumple zones increase the time taken to stop, reducing the force.
Quick check
Part 11 of 19
Reset break
Part 12 of 19
Pause
That's sitting 3 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 13 of 19
Explore the idea
Part 14 of 19
Worked example
Worked answer: explain how a crumple zone reduces injury in a crash (3 marks)
The crumple zone deforms, so the car takes longer to come to a stop (1). The change in momentum is the same, but it happens over a greater time, so the rate of change of momentum is smaller (1). Since force equals the rate of change of momentum, the force on the occupants is reduced, lowering the risk of injury (1).
Challenge round
Part 15 of 19
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Reset break
Part 16 of 19
Pause
That's sitting 4 of 5 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 17 of 19
Game · Recall cards
Newton's second law is expressed as
Card 1 of 4
Mastery quiz
Part 18 of 19
Marked quiz
End of lesson quiz: Forces, motion and momentum
4 questions, marked with the reasoning shown. No timer.
1. Newton's second law is expressed as
2. The area under a velocity–time graph gives
3. Thinking distance is increased by
4. Momentum is calculated as
Lesson round-up
Part 19 of 19
Lesson round-up
Ready when you are
Quiz score
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Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?
Ask LunaPart 1 of 19 · Watch & discover