Speed

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Lesson notes

What is Speed?

**Speed** is a measure of the distance an object moves in a certain time.
Common units include miles per hour (mph) and kilometres per hour (km/h).
In physics, speed is usually measured in **metres per second (m/s)**.
Constant speed means the same distance is covered each second (e.g., 30 m/s = 30 m every second).

Calculating Speed

The equation for speed is: **Speed = Distance ÷ Time**.
Example: A car travels 400 m in 20 s → Speed = 400 ÷ 20 = **20 m/s**.
Always include the correct units (m/s) in your answer.

Calculating Distance

Rearrange the speed equation: **Distance = Speed × Time**.
Example: An athlete runs at 8 m/s for 50 s → Distance = 8 × 50 = **400 m**.

Calculating Time

Rearrange the speed equation: **Time = Distance ÷ Speed**.
Use this when you know distance and speed and need to find time.

Relative Speed

The speed of one object relative to another can be found by adding speeds.
Example: Car at 30 m/s, train 20 m/s faster → train speed = 30 + 20 = **50 m/s**.

Units and Conversions

Speed units: m/s (metres per second), km/h (kilometres per hour), mph (miles per hour).
In calculations, ensure distance and time are in compatible units (e.g., metres and seconds).

Worked Examples

Cyclist: 120 m in 20 s → Speed = 120 ÷ 20 = **6 m/s**.
Runner: 1500 m in 500 s → Speed = 1500 ÷ 500 = **3 m/s**.
Dog walker: 1200 m in 1000 s → Speed = 1200 ÷ 1000 = **1.2 m/s**.

Key Points

Speed = Distance ÷ Time is the core formula.
You can rearrange it to find distance or time.
Constant speed means the object covers equal distances in equal time intervals.

Slides

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Practice questions

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1.What is speed a measure of?
Easy
- AThe distance an object has moved in a certain time
- BThe time an object takes to move a certain distance
- CThe force acting on an object
- DThe mass of an object
2.Which of the following is the correct equation for speed?
Easy
- ASpeed = Distance × Time
- BSpeed = Distance ÷ Time
- CSpeed = Time ÷ Distance
- DSpeed = Distance + Time
3.An object is travelling at a constant speed of 20 m/s. How far does it travel every second?
Easy
- A20 m
- B10 m
- C40 m
- D5 m
4.A car is travelling at 20 m/s and a train is travelling 10 m/s faster than the car. What is the speed of the train?
Easy
- A10 m/s
- B20 m/s
- C30 m/s
- D200 m/s
5.A cyclist travels a distance of 120 m in 20 seconds. What is the cyclist's speed?
Medium
- A6 m/s
- B2400 m/s
- C0.17 m/s
- D100 m/s
6.A runner travels 1500 m in 500 s. What is the runner's speed?
Medium
- A3 m/s
- B750000 m/s
- C0.33 m/s
- D1000 m/s
7.A sound wave travels 686 m in 2 seconds. What is the speed of sound?
Medium
- A343 m/s
- B1372 m/s
- C344 m/s
- D684 m/s
8.Light travels 4,500,000,000 m in 15 seconds. What is the speed of light?
Hard
- A300,000,000 m/s
- B300,000 m/s
- C67,500,000,000 m/s
- D4,500,000,015 m/s

Revision notes

## Speed - **Speed** measures how fast an object moves: distance covered in a given time. - Common units: miles per hour (mph), kilometres per hour (km/h). In physics: **metres per second (m/s)**. - Constant speed means equal distance each second (e.g., 30 m/s → 30 m every second). ### Key Formula $$\text{Speed} = \frac{\text{Distance}}{\text{Time}}$$ - To find distance: $$\text{Distance} = \text{Speed} \times \text{Time}$$ - To find time: $$\text{Time} = \frac{\text{Distance}}{\text{Speed}}$$ ### Example Calculations 1. **Finding speed**: Car travels 400 m in 20 s. $$\text{Speed} = 400 \div 20 = 20 \text{ m/s}$$ 2. **Finding distance**: Athlete runs at 8 m/s for 50 s. $$\text{Distance} = 8 \times 50 = 400 \text{ m}$$ ### Relative Speed - If one object is faster than another, add the speeds. - Car at 30 m/s, train 20 m/s faster → train speed = 30 + 20 = 50 m/s.

Speed: A measure of the distance an object has moved in a certain time.
Metres per second (m/s): The standard unit of speed in physics.
Constant speed: When an object travels the same distance every second.
Speed = Distance ÷ Time: The equation to calculate speed.
Distance = Speed × Time: The equation to calculate distance when speed and time are known.
Relative speed: The speed of one object compared to another; found by adding speeds if moving in the same direction.

Flashcards

What is speed?

Speed is a measure of the distance an object has moved in a certain time.

What units are commonly used for speed in physics?

In physics, speed is usually measured in metres per second (m/s).

What does a constant speed of 30 m/s mean?

It means the object travels a distance of 30 metres every second.

State the equation to calculate speed.

Speed = Distance ÷ Time

How do you calculate distance if you know speed and time?

Distance = Speed × Time

A car travels 400 m in 20 s. Calculate its speed.

Speed = 400 m ÷ 20 s = 20 m/s

An athlete runs at 8 m/s for 50 s. Calculate the distance.

Distance = 8 m/s × 50 s = 400 m

A car is travelling at 30 m/s and a train is 20 m/s faster. What is the train's speed?

The train's speed is 30 m/s + 20 m/s = 50 m/s.

An object travels at constant speed 20 m/s. How far does it travel each second?

It travels 20 metres each second.

An object travels at constant speed 8 m/s. How far does it travel each second?

It travels 8 metres each second.

A car is travelling at 20 m/s, and a train is 10 m/s faster. State the speed of the train.

The train's speed is 30 m/s.

A cyclist travels 120 m in 20 s. Calculate the speed.

Speed = 120 m ÷ 20 s = 6 m/s

A runner travels 1500 m in 500 s. Calculate the speed.

Speed = 1500 m ÷ 500 s = 3 m/s

A dog walker travels 1200 m in 1000 s. Calculate the speed.

Speed = 1200 m ÷ 1000 s = 1.2 m/s

A sound wave travels 686 m in 2 s. Calculate the speed of sound.

Speed = 686 m ÷ 2 s = 343 m/s

Light travels 4,500,000,000 m in 15 s. Calculate the speed of light.

Speed = 4,500,000,000 m ÷ 15 s = 300,000,000 m/s

A car travels at 25 m/s for 400 s. Calculate the distance.

Distance = 25 m/s × 400 s = 10,000 m

A motorbike travels at 40 m/s for 20 s. Calculate the distance.

Distance = 40 m/s × 20 s = 800 m

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