ScienceGCSE physics: forces, motion and waves30 min★★★ difficulty

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
15 parts to scroll through
4 quick checks
Marked quiz at the end
Gentle pace: short sittings with pauses

Words to know

motionbehaviourcalculatenewtongraphs

Scroll down — the lesson carries on below

Part 1 of 15 · Discover7%

Watch & discover

Part 1 of 15

Watch first

Forces, motion and momentum

An English teaching video on this topic from Cognito. Watch it, then scroll down for the lesson.

In a nutshell

Apply the laws of motion and wave behaviour to explain and calculate.

Learning cycle

Part 2 of 15

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 15

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.

Explore the idea

Part 4 of 15

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 5 of 15

Quick check

Newton's second law is expressed as

Quick check

Part 6 of 15

Quick check

The area under a velocity–time graph gives

Reset break

Part 7 of 15

Pause

That's sitting 1 of 2 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.

Stop here for now

Learning cycle

Part 8 of 15

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 9 of 15

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 10 of 15

Quick check

Thinking distance is increased by

Quick check

Part 11 of 15

Quick check

Momentum is calculated as

Explore the idea

Part 12 of 15

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 13 of 15

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

Mastery quiz

Part 14 of 15

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 15 of 15

Lesson round-up

Ready when you are

Quiz score

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Games

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Points this lesson

Best run

0 in a row

Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?

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Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Case study

Why the school greenhouse failed

A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.

The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.

The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.

Written for Good Learning Co.

Reading questions

Name the variable the club changed the second time, and one variable they kept the same.
Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
Write a conclusion for the club's report, saying how far the evidence supports it.

Method and results
Writing
Write the aim, what you changed, what you measured and what you kept the same, then record your results in a table.
1 page + results table
Conclusion
Writing
Explain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.
6–8 sentences
Labelled diagram
Diagram
Draw the apparatus or the process in pencil, label it fully, and photograph it.
1 labelled diagram
Reading and notes
Reading
Read the lesson text again and write the key ideas in your own words.
Half a page of notes

Write your answer, notes or working here

Saved as you type.

Photos of paper work, diagrams or working outHow many minutes did the written work take?

Part 1 of 15 · Watch & discover

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