Year 9 Forces: Motion, Pressure and Turning Effects
Key Stage 3 | Ages 13–14 | Beginner
Instructions: Work through the activities in order. Use the equations and data given, show your working in the answer boxes, and include units where appropriate. For calculations, remember to convert units when needed.
Speed, Distance and Time
Use speed = distance ÷ time. Rearrange it when needed: distance = speed × time, and time = distance ÷ speed. Convert minutes to hours where necessary, and write a suitable unit with each answer.
1. A cyclist travels 600 m in 120 s. Calculate the cyclist's speed in m/s. [2 marks]
2. A car travels at 20 m/s for 15 s. Calculate the distance travelled. [2 marks]
3. A runner covers 1,500 m at an average speed of 5 m/s. Calculate the time taken in seconds. [2 marks]
4. A bus travels 30 km in 0.5 h. Calculate its average speed in km/h. [2 marks]
Interpreting a Distance–Time Graph
The table gives points from a distance–time graph for a walker. Distance is measured from the starting point. Use the change in distance divided by the change in time to find speed; a horizontal section means the walker is stationary.
| Time (min) | Distance (m) |
| 0 | 0 |
| 2 | 120 |
| 4 | 240 |
| 6 | 240 |
1. Calculate the walker's speed from 0 to 2 minutes in m/min. [2 marks]
2. How far has the walker travelled from the starting point at 4 minutes? [1 mark]
3. During which time interval is the walker stationary? [1 mark]
4. Calculate the walker's speed from 2 to 4 minutes in m/min. [2 marks]
Relative Motion
Compare the objects' speeds and directions. For objects moving in the same direction, subtract the smaller speed from the larger speed to find their relative speed. For objects moving towards one another, add their speeds.
1. A train travels east at 18 m/s. A second train on a parallel track travels east at 12 m/s. What is the first train's speed relative to the second? [2 marks]
2. Two cyclists ride towards each other at 6 m/s and 4 m/s. What is their closing speed? [2 marks]
3. A car travels north at 15 m/s. A bus travels south at 10 m/s. What is their relative speed? [2 marks]
4. A walker moves at 1.5 m/s on a travelator moving in the same direction at 0.5 m/s. What is the walker's speed relative to the ground? [2 marks]
Pressure on Surfaces and in Fluids
For a solid surface, use pressure = force ÷ area. Pressure is measured in pascals (Pa), where 1 Pa = 1 N/m². For a liquid, use pressure = depth × density × gravitational field strength; take water's density as 1,000 kg/m³ and gravitational field strength as 10 N/kg. In a gas, particle collisions create pressure.
1. A force of 120 N acts over an area of 0.4 m². Calculate the pressure in Pa. [2 marks]
2. The same 120 N force acts over an area of 0.2 m². Calculate the pressure in Pa. [2 marks]
3. Calculate the water pressure at a depth of 2 m using p = h × ρ × g. [2 marks]
4. Explain, using particle collisions, why compressing a gas into a smaller volume can increase its pressure. [2 marks]
Moments and Levers
A moment is the turning effect of a force. Use moment = force × perpendicular distance from the pivot, with distance in metres and moment in newton metres (N m). For a balanced lever, the clockwise moments equal the anticlockwise moments.
1. A 10 N force acts 0.3 m from a pivot. Calculate its moment. [2 marks]
2. A 20 N force acts 0.5 m from a pivot. Calculate its moment. [2 marks]
3. A 12 N force acts 0.4 m from a pivot. What force, acting 0.8 m from the pivot on the opposite side, balances it? [3 marks]
4. A lever has a 15 N load 0.2 m from the pivot. A force is applied 0.6 m from the pivot on the other side. Calculate the force needed to balance the lever. [3 marks]
Contact and Non-Contact Forces
Classify each force as contact or non-contact. Contact forces require objects to touch; non-contact forces act at a distance. Then use the named forces to answer the final question.
1. Is friction between a shoe and the floor a contact or non-contact force? [1 mark]
2. Is the gravitational force between Earth and the Moon a contact or non-contact force? [1 mark]
3. Is the magnetic force between two magnets a contact or non-contact force? [1 mark]
4. Is the air resistance acting on a falling parachute a contact or non-contact force? [1 mark]
5. Name one non-contact force and one contact force from Questions 1–4. [2 marks]
Activity 1: 5 m/s ; 300 m ; 300 s ; 60 km/h
Activity 2: 60 m/min ; 240 m ; 4–6 minutes ; 60 m/min
Activity 3: 6 m/s ; 10 m/s ; 25 m/s ; 2 m/s
Activity 4: 300 Pa ; 600 Pa ; 20,000 Pa ; Compression increases the frequency of particle collisions with the container walls, so pressure increases.
Activity 5: 3 N m ; 10 N m ; 6 N ; 5 N
Activity 6: Contact ; Non-contact ; Non-contact ; Contact ; Non-contact: gravity or magnetic force; contact: friction or air resistance
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