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Science lesson plan · 11th grade (Year 12 in England) · 30 minutes

Orbits and orbital speed (v = 2Ï€r / T)

Space

CCSS NGSS.HS-ESS1-4CCSS NGSS.HS-PS2-4England: GCSE Physics: Space physics (orbital motion)

Objective and success criteria

Students will: Orbits and orbital speed (v = 2Ï€r / T).

  • I can answer questions on today's skill on my own, without help.
  • I can explain each step and say why it works.
  • I can check my answer and spot a mistake.

Before and after

Needs first: Earth's orbit, years and seasons; Scalars and vectors: distance vs displacement, speed vs velocity

Leads to: Newton's law of gravitation and field strength; Circular motion and centripetal force

Materials: Torch and ball for a Sun-Earth-Moon model, Space images, Mini whiteboards, A diagram or short video clip of the idea, Printed student sheet (below).

Warm-up · 4 min

  • 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. What causes the seasons? (the Moon blocking sunlight / the Sun getting hotter and colder / Earth getting closer to and further from the Sun / the tilt of Earth's axis as it orbits the Sun) → the tilt of Earth's axis as it orbits the SunPrompt: Earth is actually closest to the Sun in early January.
  2. Is acceleration 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 8 years in a row? → 2922Prompt: How many leap days are there in 8 years?

Hook · 3 min

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

I do: model it · 7 min

  • 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 = 2Ï€r ÷ T; give 1 decimal place)
  • Step 1: T = 101 × 60 = 6060 s
  • Step 2: 2Ï€ × 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.

We do: guided practice · 6 min

  • 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 geostationary satellite orbits at a radius of about 42160 km from Earth's centre, taking 1436 minutes per orbit. What is its orbital speed, in km/s? (v = 2πr ÷ T; give 1 decimal place) → 3.1 km/sPrompt: Convert the period to seconds.
  2. How does orbital speed change for a smaller (lower) stable orbit? (It must move faster / Speed does not depend on radius / It must move slower / It stops) → It must move fasterPrompt: Gravity is stronger closer to Earth.

You do: independent practice · 7 min

  • 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 6 questions are on the student sheet below, with answers in the key.

Exit ticket · 3 min

  • Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.
  1. A geostationary satellite orbits at a radius of about 42160 km from Earth's centre, taking 1436 minutes per orbit. What is its orbital speed, in km/s? (v = 2πr ÷ T; give 1 decimal place) → 3.1 km/sPrompt: Convert the period to seconds.
  2. Orbits: which statement is NOT true? (The Moon is a natural satellite of the Earth. / Gravity provides the force that keeps planets and satellites in orbit. / A satellite in a circular orbit has a constant velocity. / Astronauts on the ISS feel weightless because they are in free fall around Earth.) → A satellite in a circular orbit has a constant velocity.Prompt: Is velocity the same as speed?

Watch out for

  • Everyday meanings of words getting in the way of the science meaning: define key words explicitly.
  • Remembering facts without the reason: ask "why?" and "what is the evidence?"

Support and stretch

Support

  • Review first: Earth's orbit, years and seasons.
  • Use concrete materials: torch and ball for a sun-earth-moon model.
  • Give the first step of each question, or a partly worked example to finish.
  • Pair with a confident partner for the guided practice.

Stretch

  • Move on to: Newton's law of gravitation and field strength; Circular motion and centripetal force.
  • Explain a common mistake in writing and how to fix it.
  • Write a word problem that uses today's skill, then solve a partner's.

Homework and more practice

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

Free lesson plan from eurekami.com/lesson-plan-builder

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Orbits and orbital speed (v = 2Ï€r / T)

Name

Date

Score/ 6

  1. Question 1

    A geostationary satellite orbits at a radius of about 42160 km from Earth's centre, taking 1436 minutes per orbit. What is its orbital speed, in km/s? (v = 2πr ÷ T; give 1 decimal place)

    Answerkm/s

  2. Question 2

    How does orbital speed change for a smaller (lower) stable orbit?

    • A. It stops
    • B. It must move faster
    • C. Speed does not depend on radius
    • D. It must move slower

  3. Question 3

    Orbits: which statement is NOT true?

    • A. The Moon is a natural satellite of the Earth.
    • B. The force on an orbiting object points towards the centre of the orbit.
    • C. Gravity provides the force that keeps planets and satellites in orbit.
    • D. There is no gravity at the height of the ISS.

  4. Question 4

    A satellite moves at a steady speed in a circular orbit. Why is it accelerating?

    • A. Its engines are always on
    • B. Its speed increases every orbit
    • C. Its direction is always changing, so its velocity changes
    • D. It is not accelerating

  5. Question 5

    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)

    Answerkm/s

  6. Question 6

    The Moon takes about 27 days to orbit Earth, but the ISS takes about 90 minutes. Why the difference?

    • A. The ISS orbits much closer, so it must move faster around a much shorter path
    • B. The Moon orbits a different planet
    • C. The Moon is pushed by the Sun
    • D. The ISS has no mass

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Answer key: Orbits and orbital speed (v = 2Ï€r / T)

  1. 1. 3.1 km/s

  2. 2. B. It must move faster

  3. 3. D. There is no gravity at the height of the ISS.

  4. 4. C. Its direction is always changing, so its velocity changes

  5. 5. 7.5 km/s

  6. 6. A. The ISS orbits much closer, so it must move faster around a much shorter path