Year 7 Science · Unit 4 · Lesson 14

Unit Synthesis: Observing the Universe

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Date

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Learning Goals

Tell observations from inferences, and correct common mistakes about the sky.
Explain how the Moon’s pull and Earth’s spin give two high tides a day.
Process repeated crater results: find a mean, deal with an odd result, plot a graph and conclude.

Warm Up

True or false? Fix the false ones

Circle T or F. If a statement is false, correct it on the line.

1. Our model of the Solar System changed from an Earth-centred picture to a Sun-centred one as new evidence came in.

Correct it:

2. In science, an idea never changes once it has been written down.

Correct it:

3. Aboriginal and Torres Strait Islander Cultural Knowledges link the Moon, the stars and the tides.

Correct it:

4. Most beaches get one high tide and one low tide each day.

Correct it:

5. The Moon makes its own light, and that light grows and fades to give the phases.

Correct it:

Your Turn

Observation or inference?

Each statement comes from a crater investigation. Write observation (something noticed or measured directly) or inference (a conclusion worked out from observations).

Statement	Observation or inference?
The ball must have been moving faster when it landed.
The crater measured 42 mm across with a ruler.
Flour was pushed up into a ring around the dent.
A higher drop probably gives the ball more energy.
The crater from 100 cm was wider than the crater from 20 cm.

Cause and effect: two high tides

Fill the two empty boxes. Each box is caused by the one before it, and row 2 carries on from the end of row 1.

The Moon’s gravity pulls on Earth’s oceans.

Most beaches get two high tides and two low tides each day.

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Go Deeper

Read the data: heavier balls

Scenario

Noah’s class wanted to know whether a heavier ball makes a wider crater. They filled the same hollow plastic ball with different amounts of sand, taped it shut and dropped it from 50 cm into the same tray of flour, three times for each mass.

Table 1. Crater diameter (mm) for each mass of ball

Mass of ball (g)	Trial 1	Trial 2	Trial 3	Mean
20	30	31	29	30
40	35	37	36
60	40	42	55
80	45	44	46	45
100	48	49	47	48

Source: sample class results.

1. Calculate the mean crater diameter for the 40 g ball. Write it in Table 1.

Apply 2 marks

Answer mm

2. One result for the 60 g ball does not fit the others. Name it, say what the class should do with it, and work out the mean for 60 g.

Analyse 3 marks

3. Plot the five means, with mass along the bottom. Label both axes with units and draw a smooth line.

Apply 3 marks

Graph 1. Title: ______________________________

4. Write a conclusion: does a heavier ball make a wider crater? Use the trend and two numbers from Table 1.

Analyse 2 marks

Show What You Know

5. Pick one: Moon phases, tides or the Solar System model. Describe the path from people watching the sky to trusted scientific understanding of it.

Analyse 6 marks

Answer Key (for teachers)

True or false

1. True. 2. False: an idea can change when new evidence appears. 3. True. 4. False: most beaches get two high and two low tides a day. 5. False: the Moon’s half facing the Sun is lit; phases come from seeing different amounts of that lit half as it orbits.

Observation or inference?

Reading down: inference; observation; observation; inference; observation.

Cause and effect: two high tides

Box 1: the ocean is raised into two bulges (1). Box 2: as Earth spins, each beach passes through both bulges every day (1). [2 marks]

Read the data: Question 1

(35 + 37 + 36) ÷ 3 (1) = 36 mm (1). [2 marks]

Question 2

Trial 3, 55 mm (1). Leave it out of the mean, or repeat that drop (1). (40 + 42) ÷ 2 = 41 mm (1). [3 marks]

Question 3

Axes labelled “Mass of ball (g)” and “Mean crater diameter (mm)” with even scales (1); five points plotted correctly (30, 36, 41, 45, 48) (1); smooth rising line (1). [3 marks]

Question 4

Yes: the heavier the ball, the wider the crater (1), from 30 mm at 20 g to 48 mm at 100 g (1). [2 marks]

Question 5

Marking guide: 1 correct cause or model; 1 an observation; 1 an inference from it; 1 repeated observation over time shows the pattern; 1 new evidence or instruments test and improve the idea; 1 links to the big idea. [6 marks]

Model answer (phases): Phases come from seeing different amounts of the Moon’s lit half as it orbits Earth. People observed the Moon’s shape change night after night and inferred that only part of the lit side faces us. Watching over many months showed a repeating cycle that can be predicted. Better instruments and new evidence let scientists test this idea, turning careful observation into testable knowledge.

Common error: averaging the 55 mm result into the 60 g mean.