Speed Knowledge Organiser

Topic OverviewForces and motion Pairs of forces that are of the same size are balanced. When the forces are balanced,

the resultant (overall) force is zero and the object is in equilibrium.o If the object is moving, its speed will be constant (it will not change). o If the object is not already moving, it will remain stationary.

Pairs of forces that are of a different size are unbalanced. When the forces are unbalanced, the resultant force is not zero. o The object will speed up (accelerate) or slow down (decelerate).

Drag Drag is a special type of friction which occurs when objects move through fluids

(liquids and gases). Drag forces act opposite to the direction of travel and slow objects down. Drag can be a useful force. Look at the diagram above. The parachute has a big

surface area, this means more air particles hit it, this in turn increases the size of the drag force and slows the car down.

At other times, drag is not useful. Think about when you are gliding in swimming, the drag force slows you down. To overcome this, you make yourself have a more streamlined shape.

Distance-time graphs Distance-time graphs can be used to show what happens to the speed of an object

over time:o All the lines on the graph are straight – this shows that the speed is constant at

each stage of the journey. Curved lines show acceleration and deceleration.o The gradient of the slope shows you how fast the object is travelling – when the

line is steeper, the object is travelling faster.o When the line is horizontal, the object is stationary (not moving).

You can work out the speed for each stage of the journey by calculating the gradient of the slope. o At stage A: Lisa travels 1000m in 1000s. Her speed is 1000m/1000s = 1m/s.o At stage B: Lisa travels 0m as she waits for 500s. Her speed is 0m/500s = 0m/s.o At stage C: Lisa travels 3000m in 1000s. Her speed is 3000m/1000s = 3m/s.o At stage D: Lisa travels 0m as she waits for 100s. Her speed is 0m/1000s = 0m/s.o The average speed for the entire journey can also be worked out from the graph.

Lisa travelled 4000m to get to school and it took her 2500s to arrive. Therefore, her average speed = 4000m/2500s = 1.6m/s

Speed The speed of an object tells you how fast it is going. The faster an object is moving, the quicker it will travel a certain distance, for

example: most people can walk 5000m in an hour, but a snail can only cover 1m in that time.

As long as we know the distance covered and the time taken, we can calculate the speed of an any object using this equation:

The units for distance and time are used to give the units for speed. Look at the example questions below:

Speed Key Fact Test 1-10

No Questions Answers

1 What do we call pairs of forces that are equal in size? Balanced forces

2 What do we call pairs of forces that are different in size? Unbalanced forces

3 What do we call the overall force acting on an object? Resultant force

4 How do we calculate the resultant force? By working out the difference between two forces in a pair

5 What does it mean if an object is travelling at a constant speed?

It is travelling at the same speed (it is not getting faster or slower)

6 What does stationary mean? The object is not moving.

7 What can you tell about the speed of an object if the resultant force on it is zero?

The speed remains constant (this could mean the object is stationary)

8 What can you tell about the speed of an object if the resultant force is not zero?

The speed is changing (the object is accelerating or decelerating)

9 What does the word acceleration mean? An object speeds up

10 What does the word deceleration mean? An object slows down

Speed Key Fact Test 11-20

No Questions Answers

11 What is the name of the force that acts when an object moves through a fluid? Drag

12 What is the effect of drag on the speed of an object?

Drag causes the object to slow (decelerate)

13 How can drag be reduced? By making the object streamlined.

14 On a distance time graph, what does it mean when the line is horizontal?

The object is stationary (not moving).

15 On a distance time graph, what does it mean when the line is diagonal?

The object is moving at a constant speed.

16 On a distance time graph, what does it mean if the line is steeper?

The object is travelling at a faster constant speed.

17 How is speed calculated from a distance-time graph?

By calculating the gradient (vertical change horizontal change)

18What do we call the measure of the distance covered by an object in a specific amount of time?

Speed

19 Which two measurements do you need to know to calculate speed?

The distance travelled and the time taken.

20 What is the equation used to calculate speed?

Speed = distance time