• Quick retrieval from earlier learning (Earth's orbit, years and seasons; Scalars and vectors: distance vs displacement, speed vs velocity). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. When it is summer in the UK, the Northern Hemisphere is… (not tilted / furthest from the Sun because of distance / tilted away from the Sun / tilted towards the Sun) → tilted towards the SunPrompt: Summer comes with longer days and more direct sunlight.
2. Is displacement a scalar or a vector quantity? (scalar (size only) / vector (size and direction)) → vector (size and direction)Prompt: Does it make sense to give it a direction?
3. A year is 365 days, plus one extra day every 4 years (a leap year). How many days are there in 12 years in a row? → 4383Prompt: How many leap days are there in 12 years?

• Ask why we see the Moon change shape over a month.
• Share the objective: Orbits and orbital speed (v = 2πr / T). Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: A polar weather satellite orbits at a radius of about 7200 km from Earth's centre, taking 101 minutes per orbit. What is its orbital speed, in km/s? (v = 2πr ÷ T; give 1 decimal place)
• Step 1: T = 101 × 60 = 6060 s
• Step 2: 2π × 7200 = 45239 km
• Step 3: 45239 ÷ 6060 = 7.47
• Step 4: So the answer is: 7.5 km/s
• Answer: 7.5 km/s
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. A GPS satellite orbits at a radius of about 26560 km from Earth's centre, taking 718 minutes per orbit. What is its orbital speed, in km/s? (v = 2πr ÷ T; give 1 decimal place) → 3.9 km/sPrompt: Convert the period to seconds.
2. Why are geostationary satellites useful for TV broadcasts? (They orbit once every 24 hours, so they stay above the same point on Earth / They pass over the poles / They do not move / They orbit very close to the ground) → They orbit once every 24 hours, so they stay above the same point on EarthPrompt: Dishes can point in a fixed direction.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. The Moon takes about 27 days to orbit Earth, but the ISS takes about 90 minutes. Why the difference? (The ISS orbits much closer, so it must move faster around a much shorter path / The ISS has no mass / The Moon orbits a different planet / The Moon is pushed by the Sun) → The ISS orbits much closer, so it must move faster around a much shorter pathPrompt: Compare their distances from Earth.
2. Orbits: which statement is NOT true? (There is no gravity at the height of the ISS. / The Moon is a natural satellite of the Earth. / Gravity provides the force that keeps planets and satellites in orbit. / The force on an orbiting object points towards the centre of the orbit.) → There is no gravity at the height of the ISS.Prompt: Is velocity the same as speed?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-11.