Year 7 Science · Unit 3 · Lesson 11
Foundation Worksheet
Learning Goals
Sort it
Ask “Is this a force? Does it need touching?” Write each item in the correct box. The boxes do not hold the same number of items.
Contact force
Non-contact force
Not a force (a tool or a unit)
Fill the gap
Choose words from the word bank. Each word is used at most once. Two words are not needed: cross them out.
A force is a push or a pull. It is measured in with a . On a force diagram, a longer arrow shows a force. If the arrows cancel out, the forces are and the motion does not change; if they do not cancel, the forces are and the motion changes. The pull of gravity on an object’s mass is its . opposes motion between two surfaces and transfers movement energy to heat. A or a pulley changes the size of the force needed for a task.
A bucket on a spring scale
Scenario: weighing sand
A bucket of sand with a mass of 3 kg hangs, not moving, from a spring scale. On Earth, g is about 10 N/kg.
1. Calculate the weight of the bucket of sand. Use W = mg.
W = N
2. Draw a force diagram of the bucket. Show the two forces as labelled arrows with their sizes in newtons. Then write whether the forces are balanced or unbalanced.
The forces are
Read the data: Kai’s skateboard
Scenario: three surfaces
Kai pushes off once, with the same push each time, then rolls on flat ground until he stops. He tries three surfaces.
| Surface | Smooth concrete | Rough bitumen | Short grass |
|---|---|---|---|
| Distance rolled (m) | 18 | 11 | 3 |
Source: sample class results.
3. On which surface was the friction force largest? Use Table 1 to explain how you know.
4. While Kai is slowing down on the concrete, name the force that slows him and say whether it is a contact or non-contact force. Are the forces along the ground balanced or unbalanced? What happens to his movement energy?
5. A 4 kg melon is weighed with a spring scale on Earth. Then it is taken to the Moon, where gravity is weaker. Explain what happens to the melon’s mass and to its weight. Use W = mg in your answer.
Sort it
Contact force: friction; tension in a rope; air resistance; a hand pushing a trolley. Non-contact force: magnetic force; gravitational force; electrostatic force. Not a force: a spring scale (measures forces); the newton (the unit of force).
Fill the gap
newtons; spring scale; bigger; balanced; unbalanced; weight; Friction; lever. Not used: kilograms (a unit of mass, not force) and temperature.
A bucket on a spring scale
1. W = 3 × 10 (1) = 30 N (1). [2 marks]
2. Arrow down labelled weight (or gravity), 30 N (1); arrow up labelled pull of the spring scale (tension), 30 N, the same length (1); balanced, because the bucket is not moving and the arrows cancel (1). [3 marks]
Read the data: Kai’s skateboard
3. Short grass (1). With the same push, Kai stopped in the shortest distance, 3 m, so the force slowing him was largest there (1). [2 marks]
4. Friction between the wheels and the ground (accept air resistance too) (1); a contact force (1). Unbalanced: nothing pushes him forward, so there is a net force backward (1). His movement energy is transferred to heat (and a little sound) in the wheels and ground; it is not destroyed (1). [4 marks]
Question 5
Marking guide: 1 Earth weight W = 4 × 10 = 40 N; 1 the mass stays 4 kg; 1 because mass is the amount of matter, and no matter is added or removed; 1 the weight becomes smaller; 1 because weight is the pull of gravity, and W = mg gives a smaller W when g is smaller. [5 marks]
Model answer: On Earth the melon’s weight is W = mg = 4 × 10 = 40 N. On the Moon its mass is still 4 kg, because it is made of the same amount of matter. Its weight is smaller than 40 N, because weight is the pull of gravity on the mass and the Moon’s g is smaller, so W = mg gives a smaller force.
Common error: saying the melon “weighs 4 kg”. Kilograms measure mass; weight is a force in newtons.