Changing speed | Science | Quizalize & Oak National Academy

Starter quiz

Which of these is a force measurement?

30 kg

30 m

30 m/s

30 N ✓

30 J
What feature of a distance-time graphs shows the speed?

The horizontal axis.

The verical axis.

The gridlines.

The gradient of the line. ✓

The number of divisions on each axis.
Which of these show how forces should be represented on diagram?

Is drawn as an arrow. ✓

Has a special colour for each type of force.

Starts at the point where the force acts. ✓

Points in the direction the force acts. ✓

Must always have a pair drawn with it.
Ben pushes a shopping trolley so it is moving quickly but then falls and lets go. Which of these forces still act on the trolley after he has let go?

Ben's push.

A driving force keeping the trolley moving.

A friction force due to the ground. ✓

A normal contact force due to the ground. ✓

A gravitational force due to Earth. ✓
A student is measuring the average speed of a trolley between two points marked on a ramp. Which measurements do they need to make to find the speed?

The mass of the trolley.

The angle of the ramp.

The time for the trolley to pass between the markers. ✓

The time the trolley took to reach the markers.

The distance between the two markers. ✓
What is the average speed of this object?

0 m/s

0.15 m/s ✓

6.6 m/s

51 m/s

69 m/s

Exit quiz

Match the key word with the description.

resultant force

⇔

The sum of forces on an object, accounting for direction. ✓

gradient

⇔

The steepness of a line on a graph. ✓

speed

⇔

Distance divided by time. ✓

dynamics trolley

⇔

A wheeled device used in motion experiments. ✓

acceleration

⇔

A change in speed. ✓
Which of the following are acceleration?

A change in the mass of an obejct.

An increase in speed. ✓

A decrease in speed. ✓

Moving at constant speed in one direction.

A change in distance.
A person drags a box along the ground using a force of 25 N towards the right. A frictional force of 20 N acts on the box as it is dragged. What is the resultant force on the box?

45 N to the right

45 N to the left

5 N to the right ✓

5 N to the left

0 N
A sprinter takes part in a 100 m race. Which statement describes how the forces change during the race?

The sprinter is at the same speed throughout the race as the force is constant.

The sprinter's speed will only increase at the start of the race.

The sprinter's speed will change as long as there is a resultant force acting. ✓

The sprinter produces a forwards force only at the start of the race.

The forces on the sprinter are always balanced so the speed stays constant.
The figure shows a distance-time graph for a car. What does the graph show?

The speed of the car is increasing.

The speed of the car is decreasing. ✓

The forces on the car are balanced.

There is a resultant force in the same direction as the car's movement.

There is a resultant force in the opposite direction to the car's movement. ✓
A firework rocket is launched vertically and it produces a large thrust for 5 s then the fuel runs out. Which answers correctly describe the rocket's motion?

The rocket will accelerate upwards for the first 5 s. ✓

The rocket will stop after 5 s.

After 5 s the speed of the rocket will start to decrease. ✓

After 5 s the rocket will start to move downwards.

The rocket's speed will still be increasing after 5 s.

Worksheet

Presentation

Video

Lesson Details

Key learning points

A resultant force can change the speed of an object.
The speed of an object changes throughout the time a resultant force is acting on it.
The greater the gradient (steeper the line) on a distance-time graph, the faster the movement.

Common misconception

Pupils can think that change in speed is instantaneous due to forces, not over a period of time.

Demonstrate that objects continue to accelerate while the force is acting. Make the force easy to understand (e.g. a pulling string).

Keywords

Resultant force - The overall effect of a set of forces acting on an object.
Speed - A measurement of how fast something is moving, found from the distance travelled divided by the time taken.
Dynamics trolley - A small wheeled cart used in motion experiments.
Acceleration - A change in speed or direction of movement.