Year 7 Science · Unit 3 · Lesson 2
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. Weight and mass are two words for the same thing.
Correct it:
2. A spring scale (newton meter) measures weight.
Correct it:
3. A 60 kg student would have less mass on Mars than on Earth.
Correct it:
4. There is no gravity in space.
Correct it:
5. On Earth, gravity pulls on each kilogram of mass with a force of about 9.8 N.
Correct it:
Sort it
Write each description in the correct box. The boxes do not hold the same number of items.
Mass
Weight
1. A 30 kg science probe lands on Mars, where g = 3.7 N/kg. Calculate the probe’s weight on Mars using W = m × g. Show your working.
Weight on Mars N
2. Kai writes: “My weight is 45 kg.” (a) Rewrite Kai’s sentence so that it is scientifically correct. (b) Calculate Kai’s weight on Earth (g = 9.8 N/kg).
Weight on Earth N
Read the data: one bag of rice, two worlds
Scenario
An astronaut weighs the same bag of rice with three instruments, first on Earth and then on the Moon. The bathroom scale shows kilograms and was set up on Earth.
| Instrument | Reading on Earth | Reading on the Moon |
|---|---|---|
| Balance scale | 10 kg | 10 kg |
| Spring scale | 98 N | 16 N |
| Bathroom scale | 10 kg | 1.6 kg |
Source: values calculated for this worksheet using g = 9.8 N/kg (Earth) and 1.6 N/kg (Moon).
3. Use W = m × g to show that the spring-scale reading on the Moon is correct.
4. Which instrument gives the same reading in both places? Explain why it does.
5. On the Moon the bathroom scale shows 1.6 kg. Has the rice lost mass? Use Table 1 to explain what a bathroom scale is really measuring.
6. Lena says: “When I go on a diet, I lose weight but my mass stays the same, just like when an astronaut goes to the Moon.” Explain what is wrong with Lena’s statement. Use the words mass, weight and g.
True or false
1. False: mass is matter (kg); weight is the pull of gravity on it (N). 2. True. 3. False: the student’s mass is still 60 kg on Mars; only the weight is smaller. 4. False: gravity acts everywhere; it weakens with distance but never switches off. 5. True.
Sort it
Mass: measured in kilograms; the amount of matter in an object; stays the same on the Moon; measured with a balance scale. Weight: measured in newtons; a force caused by gravity; smaller on the Moon than on Earth; worked out with W = m × g; measured with a spring scale. Six to eight correct = 1; all nine = 2. [2 marks]
Question 1
W = 30 × 3.7 (1) = 111 N (1, unit needed). [2 marks]
Question 2
(a) “My mass is 45 kg.” (1) (b) W = 45 × 9.8 = 441 N (1). [2 marks]
Read the data: one bag of rice, two worlds
3. W = 10 × 1.6 = 16 N, which matches the table (1). [1 mark]
4. The balance scale (1). It compares the rice with known masses; weaker gravity on the Moon pulls less on both pans together, so it still balances at 10 kg (1). [2 marks]
5. No: the balance still reads 10 kg, so the mass has not changed (1). The bathroom scale measures how hard the rice presses down, which is its weight (1). The weight falls from 98 N to 16 N (about one-sixth), so the scale, set up for Earth, shows about one-sixth of the kilograms (1). [3 marks]
Question 6
Marking guide: 1 Lena is wrong about the diet; 1 on a diet the body loses matter (atoms), so mass falls; 1 weight = m × g, so with g unchanged the weight falls too: both fall together; 1 on the Moon the mass stays the same and only g changes (9.8 to 1.6 N/kg), so only the weight falls; 1 the difference: a diet changes the mass, but moving to another place changes g. [5 marks]
Model answer: Lena is wrong about the diet. On a diet you lose matter, so your mass falls; g stays 9.8 N/kg, so W = m × g falls as well. On the Moon the astronaut keeps all their matter, so the mass stays the same, but g drops to 1.6 N/kg, so only the weight falls. A diet changes m; a trip to the Moon changes g.
Common error: giving weight in kilograms, or changing the mass when an object moves to another planet.