Speed KS3
🔢 Speed Formula
- Speed is measured in metres per second (m/s) or kilometres per hour (km/h)
- Distance is measured in metres (m) or kilometres (km)
- Time is measured in seconds (s) or hours (h)
🧠 Key Terms
| Term | Definition |
|---|---|
| Speed | How fast something moves |
| Distance | How far something travels |
| Time | How long it takes to travel that distance |
| Average Speed | Total distance ÷ total time |
| Instantaneous Speed | Speed at one specific moment |
📏 Units Table
| Quantity | Symbol | Units (common) |
|---|---|---|
| Distance | 𝑑 | metres (m), km |
| Time | 𝑡 | seconds (s), hours |
| Speed | 𝑠 | m/s, km/h |
🧮 Example 1
A car travels 100 km in 2 hours. What is its speed?
🧮 Example 2
A rabbit runs 80 metres in 10 seconds. What is its speed?
🧰 Converting Units
- 1 km = 1000 m
- 1 hour = 3600 seconds
📊 Graphs of Speed
Distance–Time Graph
- A straight diagonal line means Steady speed
- A horizontal line = stopped
- Curved line getting steeper = Acceleration = Increasing speed
- Curved line flattening out = Deceleration = Decreasing speed
- A straight diagonal line in other direction means Steady speed – returning to the point where started
| Number | Graph Segment Description | Motion Type |
|---|---|---|
| 1 | Straight diagonal line (upwards) | Steady speed |
| 2 | Horizontal line | Stationary (stopped) |
| 3 | Curved line getting steeper | Acceleration (increasing speed) |
| 4 | Curved line flattening out | Deceleration (decreasing speed) |
| 5 | Straight diagonal line (downwards) | Steady speed (returning to start) |
🎯 Practice Questions
- A cyclist covers 45 km in 3 hours. What is their speed?
- A cheetah runs 120 m in 6 seconds. What is its speed?
- Convert 90 km/h to m/s.
- Convert 15 m/s to km/h.
- A graph shows a straight line from (0, 0) to (5, 25). What is the speed?
🧠 Quick Check
- ✅ Speed is distance ÷ time
- ✅ Units must match
- ✅ Use graphs to visualise motion