Effects of force
Measuring length and time, effects of forces, speed, acceleration, distance–time graphs and turning effects.
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Before you begin
Forces change how objects move, their shape and how they turn. This topic measures lengths and times, describes what forces do, calculates speed and acceleration, reads distance–time graphs, and compares turning effects about a pivot.
Be comfortable with: reading a scale, and dividing one quantity by another.
Learning goals
- Measuring length
- Measuring time
- Changing shape or size
- Changing rest or motion
- Turning effect
- Meaning of speed and acceleration
- Average speed
- Acceleration
- Distance–time graphs
- Moment of a force
Syllabus statements covered
- use a ruler and a measuring tape to measure length
- use a digital stopwatch to measure time interval
- show an understanding of the following effects of force: — change in shape and/or size of an object
- show an understanding of the following effects of force: — change the state of rest or motion of an object (including change in speed and/or direction)
- show an understanding of the following effects of force: — bring about turning effect of an object
- show an understanding of what is meant by speed and acceleration
- recall and apply the relationship average speed = total distance / total time taken to solve problems
- recall and apply the relationship acceleration = change in speed / time taken to solve problems (for motion in one direction only)
- plot and interpret a distance-time graph
- describe the moment of a force in terms of its turning effect and relate this to everyday examples (knowledge of equations is not required)
Lessons
Work through them in order.
- Measuring length and timeChoose and read rulers, tapes and stopwatches, and repeat timings to reduce reaction-time errors.
- Effects of forcesDescribe how a force changes an object's shape, speed or direction, or makes it turn.
- Speed and accelerationCalculate average speed over a whole journey and acceleration from a change in speed.
- Distance–time graphsPlot distance–time graphs, find speed from the gradient and recognise rest as a flat section.
- Turning effectsCompare turning effects about a pivot and explain why a force further from the pivot turns more.
Practise and check
Or choose
Topic reference
Quick reference
| Quantity | Formula | Unit |
|---|---|---|
| average speed | total distance ÷ total time | m/s |
| acceleration | (final speed − initial speed) ÷ time taken | m/s² |
| On a distance–time graph | It means |
|---|---|
| straight sloping line | steady speed |
| steeper line | greater speed |
| curve getting steeper | speeding up |
| horizontal line | at rest |
Core knowledge to remember
- A force can change an object’s shape or size, its speed, its direction of motion, or how it turns.
- The gradient of a distance–time graph is the speed.
- The turning effect of a force about a pivot is greater when the same force acts further from the pivot.
- Repeating a timing and taking the mean reduces random error, but not a mistake made every time.
Common mistakes
- Dividing the final speed by the time when finding an acceleration from a non-zero starting speed.
- Reading a high point on a distance–time graph as a high speed.
- Calling the point where a force acts the pivot.
- Thinking a moving object must still be pushed.