Speed (Edexcel GCSE Maths): Revision Notes
Speed
What is speed?
Speed tells us how fast something is moving. It measures the distance travelled in a specific amount of time.
Average speed is calculated by dividing the total distance travelled by the total time taken for the journey.
Understanding speed is fundamental to many physics and mathematics problems. Speed is a scalar quantity, which means it only has magnitude (size) but no direction.
The speed formula triangle
The formula triangle is a helpful visual tool that shows the relationship between three key quantities:
- D = Distance
- S = Speed
- T = Time
D
---
|S|T|
---
To use the triangle, simply cover up the quantity you want to find with your finger. The position of the other two quantities shows you the formula to use.
The formula triangle is particularly useful in exams as it helps you remember all three formulas without having to memorise them separately. Practice using it until it becomes second nature!
Speed formulas
There are three main formulas you need to know:
- Speed = Distance ÷ Time ()
- Time = Distance ÷ Speed ()
- Distance = Speed × Time ()
These formulas work for any journey where you know two of the three values and need to find the third.
Units of speed
The most common units of speed are:
- metres per second (m/s)
- kilometres per hour (km/h)
- miles per hour (mph)
Unit Consistency is Critical!
The units in your answer will depend on the units you use in the formula. When distance is measured in kilometres and time is measured in hours, speed will be measured in km/h. Always check that your units match before calculating!
Converting between minutes and hours
For speed questions, you often need to convert between minutes and hours:
| Hours | Minutes |
|---|---|
| 1/2 | 30 |
| 3/4 | 45 |
| 2 1/4 | 135 |
Key conversion: To convert minutes to hours, divide by 60.
For example: 45 minutes = 45 ÷ 60 = 3/4 hour
Worked example
Worked Example: Distance Calculation
Question: A plane travels at a constant speed of 840 km/h for 45 minutes. How far has it travelled?
Solution:
- Draw the formula triangle and identify what you need to find (Distance)
- Check units: Speed is in km/h, so convert time to hours
- 45 minutes = 45 ÷ 60 = 3/4 hour
- Use the formula: Distance = Speed × Time
- The plane has travelled 630 km
Exam tips for speed questions
Essential Exam Strategy
When answering speed questions:
- Draw a formula triangle to help you identify the correct formula
- Make sure the units match - if speed is given in km/h, convert time into hours
- Give units with your answer - check what units are expected
- Show your working clearly for full marks
Remember!
Key Points to Remember:
- Speed measures how fast something travels (distance per unit of time)
- Use the formula triangle to find the correct formula by covering what you want to find
- Always check that your units match before calculating
- Convert minutes to hours by dividing by 60
- The three key formulas are: , , and