Astronomy & Space · Unit 8
Gravity and Orbits
Gravity, orbits, Kepler's laws, tides and weightlessness
Orbits are the clearest demonstration that gravity is universal: the same law that describes a falling apple predicts the period of a planet to several decimal places.
The unit covers how gravity works, why things orbit rather than fall in, Kepler's laws, free fall and weightlessness, and tides.
This unit breaks down into 21 short steps and 120 questions, starting at difficulty 2 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.
- Steps
- 21
- Questions
- 120
- Difficulty
- 2-3
What this unit covers
- Why Things Orbit
- Kepler's Laws
- Free Fall and Weightlessness
- How Gravity Works
- Tides and Gravity
Where this fits
Overlaps deliberately with the Physics unit of the same name. Either order works.
Where people slip
There are two high tides a day, not one. The far side bulges as well, because the water there is pulled towards the Moon less strongly than the Earth itself is.
How the unit is structured
Gravity and Orbits runs as 21 short steps that unlock in order. 15 are practice rounds and 6 are challenge rounds that pull together everything before them. Questions start at difficulty 2 and climb to 3 as you progress.
Challenge rounds
Example questions
30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 120 in the unit altogether.
Free Fall and Weightlessness
- Build the sentenceLevel 2
1. Build a true sentence about why astronauts float.
Answer: Astronauts float because they are falling
Astronauts float because they are in free fall, dropping around Earth along with their ship.
- Choose all that applyLevel 2
2. Which of these are true about astronauts in orbit? Select all that apply.
- They are constantly falling around Earthcorrect
- They feel weightlesscorrect
- There is zero gravity where they are
- Their spacecraft falls along with themcorrect
Astronauts are constantly falling around Earth with their spacecraft, so they feel weightless even though gravity is still there.
- Fact or fibLevel 2
3. Astronauts feel weightless because they are too far away for Earth's gravity to reach them.
Answer: False
Earth's gravity easily reaches the space station; astronauts feel weightless because they fall along with it.
- Fill the blankLevel 2
4. Astronauts float because they and their spacecraft are ____ together around Earth.
- fallingcorrect
- floating with no gravity
- spinning to a stop
- held still
Everything in the spacecraft falls at the same rate, so nothing presses down and everything floats.
- Multiple choiceLevel 2
5. Why do astronauts on the space station float around inside it?
- They are in constant free fall around Earthcorrect
- There is no gravity that far from Earth
- The station blocks Earth's gravity
- They wear special anti-gravity suits
They and the station are in constant free fall around Earth, so everything falls together and floats.
- Guess the numberLevel 3
6. About how many minutes does the International Space Station take to circle Earth once?
Answer: 90 minutes
The station orbits low and fast, completing one lap of Earth in roughly 90 minutes.
How Gravity Works
- Build the sentenceLevel 2
7. Build a true sentence about what gravity does.
Answer: Gravity pulls objects toward each other
Gravity is an attractive force, so it pulls objects toward each other.
- Choose all that applyLevel 2
8. Which of these are true about gravity? Select all that apply.
- More massive objects pull hardercorrect
- Gravity gets weaker with distancecorrect
- Only planets have gravity
- Gravity pushes objects apart
Gravity gets stronger with more mass and weaker with distance; it acts on everything with mass and always pulls, never pushes.
- Fact or fibLevel 2
9. Gravity gets weaker as two objects move farther apart.
Answer: True
The pull of gravity fades with distance, so far-apart objects attract each other only weakly.
- Fill the blankLevel 2
10. The more ____ an object has, the stronger its gravity.
- masscorrect
- color
- speed
- temperature
Gravity depends on mass, so more massive objects pull harder.
- Match the pairsLevel 2
11. Match each place with how much you would weigh there.
Answer: Earth = Your normal weight; The Moon = About one sixth of your weight; Jupiter = More than your Earth weight
Weight follows gravity, so you weigh normally on Earth, about a sixth as much on the Moon, and more on giant Jupiter.
- Guess the numberLevel 3
12. The Moon's gravity is about one sixth of Earth's. If you weigh 60 units on Earth, about what would you weigh on the Moon?
Answer: 10 units
Dividing 60 by 6 gives about 10, since the Moon's gravity is roughly one sixth of Earth's.
Kepler's Laws
- Fact or fibLevel 2
13. Planets move faster along their orbit when they are closer to the Sun.
Answer: True
Kepler's second law means a planet speeds up near the Sun and slows down when farther away.
- Fill the blankLevel 2
14. The Sun sits at one ____ of a planet's elliptical orbit.
- focuscorrect
- center
- corner
- edge
An ellipse has two focus points, and the Sun sits at one of them rather than the exact center.
- Match the pairsLevel 2
15. Match each orbit term with what it means.
Answer: Perihelion = Closest to the Sun; Aphelion = Farthest from the Sun; Ellipse = Oval orbit shape
Perihelion is the closest point to the Sun, aphelion the farthest, and an ellipse is the oval orbit shape.
- Multiple choiceLevel 2
16. According to Kepler, what shape are the orbits of the planets?
- Ellipses, which are ovals
- Perfect circles
- Squares
- Straight lines
Kepler showed that planets travel in ellipses, which are slightly stretched ovals.
- Choose all that applyLevel 3
17. Which of these statements about elliptical orbits are true? Select all that apply.
- An ellipse is an oval shapecorrect
- The Sun sits at one focus of the ellipsecorrect
- The planet's speed changes along the orbitcorrect
- The planet moves slowest when closest to the Sun
An ellipse is an oval with the Sun at one focus, and the planet changes speed, moving fastest when closest, not slowest.
- Odd one outLevel 3
18. Which of these is NOT one of Kepler's three laws of planetary motion?
- All orbits are perfect circlescorrect
- Orbits are ellipses
- Planets sweep equal areas in equal times
- Farther planets take longer to orbit
Kepler showed orbits are ellipses, not perfect circles, so the circle statement is the odd one out.
Tides and Gravity
- Build the sentenceLevel 2
19. Build a true sentence about how often tides happen.
Answer: Tides rise and fall twice each day
Most coasts see the water rise and fall twice each day because of Earth's two tidal bulges.
- Fact or fibLevel 2
20. Spring tides only happen during the spring season.
Answer: False
Spring tides are named for water springing up and happen whenever the Sun and Moon align, all year round.
- Fill the blankLevel 2
21. When the Sun and Moon line up, we get extra-large ____ tides.
- springcorrect
- neap
- low
- red
At new and full Moon the Sun and Moon pull together, making higher spring tides.
- Guess the numberLevel 2
22. How many high tides does a typical coast get in one day?
Answer: 2 high tides
Because Earth has two tidal bulges, most coasts pass through two high tides each day.
- Choose all that applyLevel 3
23. Which of these statements about tides are true? Select all that apply.
- The Moon is the main cause of tidescorrect
- There are usually two high tides each daycorrect
- The Sun has no effect at all on tides
- Spring tides are larger than neap tidescorrect
The Moon is the main cause, there are usually two high tides a day, and spring tides are the larger ones; the Sun does affect tides.
- Match the pairsLevel 3
24. Match each tide idea with what causes it.
Answer: Spring tide = Sun and Moon aligned; Neap tide = Sun and Moon at right angles; High tide = Ocean water bulges outward
Spring tides come when the Sun and Moon align, neap tides when they pull at right angles, and high tide is the water bulging outward.
Why Things Orbit
- Build the sentenceLevel 2
25. Build a true sentence about the Moon's motion.
Answer: The Moon orbits the Earth
The Moon travels around Earth once each month, held by Earth's gravity.
- Choose all that applyLevel 2
26. Which of these are needed for a stable orbit? Select all that apply.
- Sideways forward motioncorrect
- Gravity pulling toward the centercorrect
- A rope connecting the two objects
- The right balance of speed and gravitycorrect
A stable orbit needs sideways motion and gravity in the right balance; no rope or string is involved.
- Fact or fibLevel 2
27. Without gravity, a moving planet would travel in a straight line.
Answer: True
Gravity constantly bends a planet's path; remove it and inertia would send the planet off straight.
- Fill the blankLevel 2
28. Earth orbits the ____, held in place by its gravity.
- Suncorrect
- Moon
- Mars
- North Star
The Sun's strong gravity holds Earth and all the planets in orbit around it.
- Multiple choiceLevel 2
29. Why does the Moon stay in orbit around Earth instead of flying off into space?
- Earth's gravity keeps pulling it into a curved pathcorrect
- The Moon has no motion of its own
- The Sun pushes it back toward Earth
- The Moon is tied to Earth by a magnetic field
Earth's gravity keeps pulling the moving Moon into a curved path around it.
- Match the pairsLevel 3
30. Match each orbit idea with its description.
Answer: Low Earth orbit = Faster and closer in; Geostationary orbit = Stays over one spot; Escape velocity = Leaves orbit for good
Low orbits are fast and close, geostationary satellites hover over one spot, and escape velocity leaves orbit entirely.
Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.
How you practise
This unit mixes 14 different question formats, so you are recalling and applying rather than recognising the same layout every time.
- Build the sentence
- Choose all that apply
- Fact or fib
- Fill the blank
- Guess the number
- Match the pairs
- Multiple choice
- Odd one out
- Picture question
- Put in order
- Sort into groups
- Spell it
- True or false
- Type the answer
Practise Gravity and Orbits
120 questions across 21 steps. Start with step one and crawl at your own pace.
Play this unitRead about Gravity and Orbits
Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.
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