Speed
- Speed = distance ÷ time. It is measured in metres per second (m/s), or kilometres per hour (km/h).
- A cyclist who travels 100 m in 20 s has an average speed of 100 ÷ 20 = 5 m/s.
- Rearranging: distance = speed × time, and time = distance ÷ speed.
Distance-time graphs
- A horizontal (flat) line means the object is stationary.
- A straight sloping line means a constant speed. The steeper the line, the faster the speed.
- A curved line means the speed is changing.
- The gradient (steepness) of the line gives the speed.
Pressure
- Pressure = force ÷ area. It is measured in pascals (Pa), which are newtons per square metre (N/m²).
- A large area gives a low pressure: snowshoes, wide tractor tyres and camels' feet stop things sinking.
- A small area gives a high pressure: sharp knives, drawing pins and stiletto heels.
- Pressure in a liquid increases with depth, so dams are thicker at the bottom. Air pressure decreases as you go higher.
Moments
- A moment is the turning effect of a force: moment = force × distance from the pivot. It is measured in newton metres (N m).
- When something is balanced, the clockwise moments equal the anticlockwise moments (the principle of moments).
- Levers, such as spanners and crowbars, use a long distance to make a small force give a big turning effect.
- Averages: the mean is the total ÷ the number of values; the median is the middle value in order; the mode is the most common value.
Key terms
- Speed
- How fast something moves: distance ÷ time.
- Average speed
- The total distance divided by the total time.
- Distance-time graph
- A graph showing how far something has travelled over time.
- Gradient
- How steep a line on a graph is.
- Stationary
- Not moving.
- Pressure
- The force acting on each unit of area: force ÷ area.
- Pascal
- The unit of pressure (1 Pa = 1 N/m²).
- Moment
- The turning effect of a force: force × distance from the pivot.
- Pivot
- The point something turns around.
- Lever
- A bar that turns around a pivot to make a force more effective.
- Principle of moments
- In balance, clockwise moments equal anticlockwise moments.
- Mean
- The total of the values divided by the number of values.
- Median
- The middle value when the values are in order.
- Mode
- The most common value.