Year 7 Science · Unit 3 · Lesson 9
Foundation Worksheet
Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. To avoid parallax error, read the scale with your eye level with the pointer.
Correct it:
2. The pointer on a spring scale shows the mass of the object in kilograms.
Correct it:
3. Hooke's Law means a spring always returns to its original length, however far you stretch it.
Correct it:
4. A spring scale gives its most accurate reading when it hangs upright, not tilted.
Correct it:
5. You should zero a spring scale after you hang the object on the hook.
Correct it:
1. What is the unit of force, and what is its symbol? Name the instrument you would use to measure a force.
Sort it: the force on the hook
An apple hangs from a spring scale. Write each change in the box for what it does to the force pulling on the hook. The boxes do not hold the same number of items.
Increases the force
Decreases the force
Does not change the force
2. A pineapple has a mass of 600 g. Calculate the reading it gives on a spring scale on Earth, using weight = mass × 9.8 N/kg. Change grams to kilograms first.
Answer N
Read the data
Scenario: loading a spring
Zara hangs 100 g masses on a spring, one at a time, and measures how far it has stretched after each one. A 100 g mass weighs about 1 N. When she has finished, she takes all the masses off and finds that the spring is now 2 cm longer than when she started.
| Mass hung (g) | Force on the spring (N) | Extension (cm) |
|---|---|---|
| 100 | 1 | 2 |
| 200 | 2 | 4 |
| 300 | 3 | 6 |
| 400 | 4 | 8 |
| 500 | 5 | 13 |
Source: sample class results.
3. Describe the pattern in the first four rows of Table 1. Which law does it show?
4. What happened to the spring at 500 g? Use two pieces of evidence from the scenario and Table 1.
5. On Earth, a 2 kg mass hanging from a spring scale gives a reading of 19.6 N. An astronaut takes the same mass and the same spring scale to the Moon, where gravity is 1.6 N/kg. She also takes a balance. Explain what each instrument reads on the Moon and why they behave differently. Use the words mass, force, newton and gravity.
True or false
1. True. 2. False: it shows force (weight) in newtons; a balance measures mass. 3. False: only up to the elastic limit; beyond it the spring stays stretched. 4. True: tilted, gravity does not act fully along the spring. 5. False: zero it before you attach anything.
Question 1
The newton, symbol N (1). A spring scale, also called a newton meter (1). [2 marks]
Sort it
Increases: hang a second apple below the first; swap the apple for a heavy bag of rice; pull down on the apple with one finger. Decreases: take the scale and apple to the Moon; take the apple off the hook; support the apple from below with your palm; swap the apple for a feather. Does not change: move your eye level with the pointer (it changes what you read, not the force); hold the scale in your other hand.
Question 2
600 g = 0.6 kg; 0.6 × 9.8 (1) = 5.88 N, about 5.9 N (1). [2 marks]
Question 3
Each extra 1 N adds 2 cm: extension is proportional to force (1). Hooke's Law (1). [2 marks]
Question 4
It passed its elastic limit (1). Evidence: the extension jumped by 5 cm, to 13 cm, instead of 2 cm to 10 cm (1); with the masses off it stayed 2 cm longer, so it was permanently stretched (1). [3 marks]
Question 5
Marking guide: 1 spring scale on the Moon: 2 × 1.6 = 3.2 N; 1 a spring scale measures force (weight) in newtons, which depends on gravity, weaker on the Moon; 1 the mass is still 2 kg; 1 the balance still reads 2 kg because it compares against known masses, and weaker gravity pulls on both sides equally; 1 all four words used correctly. [5 marks]
Model answer: The spring scale reads 2 × 1.6 = 3.2 N on the Moon. It measures force, the pull of gravity on the mass, in newtons, and the Moon's gravity is weaker. The balance still reads 2 kg: it compares the object with known masses, and gravity pulls equally on both sides. The mass has not changed.
Common error: forgetting to change grams to kilograms before multiplying by 9.8.