Physics · Unit 12

Gravity and Orbits

The force that shapes the cosmos

Newton's insight was that the force pulling an apple down and the force holding the Moon are the same force, which was a genuinely radical claim about the sky obeying earthly rules.

The unit covers universal gravitation, weight and g, gravitational fields, orbits and satellites, tides, and gravity on other worlds.

This unit breaks down into 20 short steps and 119 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: 20
Questions: 119
Difficulty: 2-3

What this unit covers

Orbits and Satellites
Gravity on Other Worlds
Universal Gravitation
Weight and g
Gravitational Fields and Tides

Where this fits

Needs Forces and Newton's Laws. Overlaps with the Astronomy track's unit of the same name.

Where people slip

Astronauts are not weightless because gravity is absent. They are in free fall around the Earth, falling continuously and missing, and gravity at that altitude is nearly as strong as at the surface.

How the unit is structured

Gravity and Orbits runs as 20 short steps that unlock in order. 15 are practice rounds and 5 are challenge rounds that pull together everything before them. Questions start at difficulty 2 and climb to 3 as you progress.

Step 1 · easierStep 20 · harder

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 119 in the unit altogether.

Gravitational Fields and Tides

Choose all that applyLevel 2
1. Which statements about a gravitational field are correct?
- It is strongest close to the masscorrect
- It always points toward the masscorrect
- It points away from the mass
- It disappears completely a short distance away
A gravitational field points toward the mass and is strongest near it, weakening gradually with distance.
Fill the blankLevel 2
2. A region of space where a mass feels a gravitational force is called a gravitational ____.
- fieldcorrect
- wave
- current
- circuit
A gravitational field is the region around a mass where another mass feels a pull.
Guess the numberLevel 2
3. Most coastlines experience how many high tides each day?
Answer: 2 high tides
Most coasts have two high tides and two low tides roughly every 24 hours.
Multiple choiceLevel 2
4. What is the main cause of the ocean tides on Earth?
- The gravitational pull of the Mooncorrect
- The heat of the Sun
- Winds blowing across the sea
- The Earth's magnetic field
Tides are caused mainly by the Moon's gravity pulling on the Earth's oceans.
Fact or fibLevel 3
5. Ocean tides on Earth are caused mainly by the difference in the Moon's gravitational pull across the Earth.
Answer: True
Tides arise because the Moon pulls harder on the near side of Earth than the far side, stretching the oceans into two bulges.
Match the pairsLevel 3
6. Match each gravitational-field term to its meaning.
Answer: Gravitational potential = Energy per unit mass; Gravitational field strength = Force per unit mass; Equipotential surface = Surface of constant potential; Barycentre = Common centre of mass
Potential is energy per unit mass, field strength is force per unit mass, an equipotential has constant potential, and the barycentre is the shared centre of mass.

Gravity on Other Worlds

Fact or fibLevel 2
7. Astronauts can jump higher on the Moon than on Earth.
Answer: True
The Moon's weaker gravity means the same push sends an astronaut higher and slows their fall.
Fill the blankLevel 2
8. The strength of gravity on the Moon is about one ____ of Earth's.
- sixthcorrect
- half
- tenth
- third
The Moon's surface gravity is roughly one sixth of the Earth's.
Guess the numberLevel 2
9. A person weighs about 600 N on Earth. Roughly what would they weigh on the Moon, where gravity is about one sixth as strong?
Answer: 100 N
About 600 N divided by 6 gives roughly 100 N on the Moon.
Build the sentenceLevel 3
10. Build the phrase describing what gives a world strong surface gravity.
Answer: large mass and small radius
Surface gravity g = GM/r^2 is greatest for worlds with large mass packed into a small radius.
Choose all that applyLevel 3
11. An astronaut travels from Earth to Mars. Which statements are correct?
- Their mass stays the samecorrect
- Their weight decreases because Mars has weaker gravitycorrect
- The gravitational force on them is smaller on Marscorrect
- Their mass decreases because the gravity is weaker
Mass is unchanged, but weaker Martian gravity (about 3.7 N/kg) makes both weight and gravitational force smaller.
Match the pairsLevel 3
12. Match each world to its approximate surface gravitational field strength.
Answer: Earth = 9.8 m/s^2; Moon = 1.6 m/s^2; Mars = 3.7 m/s^2; Jupiter = 24.8 m/s^2
Surface g is about 9.8 m/s^2 on Earth, 1.6 on the Moon, 3.7 on Mars and 24.8 on Jupiter.

Orbits and Satellites

Build the sentenceLevel 2
13. Build the sentence about what holds the planets in orbit.
Answer: gravity holds the planets in orbit
The Sun's gravity provides the force that keeps the planets in their orbits.
Fact or fibLevel 2
14. The closer a satellite orbits to Earth, the faster it must travel to stay in orbit.
Answer: True
Lower orbits need higher speeds because gravity is stronger closer to the Earth.
Fill the blankLevel 2
15. The inward force that keeps a satellite in a circular orbit is called the ____ force.
- centripetalcorrect
- centrifugal
- magnetic
- elastic
Gravity acts as the centripetal force, always pointing toward the centre of the orbit.
Multiple choiceLevel 2
16. What keeps a satellite moving in orbit around the Earth?
- The pull of Earth's gravitycorrect
- The push of the air
- A rocket engine firing constantly
- The Earth's magnetic field
Gravity provides the inward (centripetal) force that keeps a satellite curving around the Earth.
Guess the numberLevel 3
17. What is the escape velocity from the surface of the Earth, in km/s?
Answer: 11.2 km/s
Escape velocity from Earth is about 11.2 km/s, given by v = sqrt(2GM/r).
Match the pairsLevel 3
18. Match each type of orbit to a typical use or property.
Answer: Geostationary orbit = TV and weather satellites over the equator; Low Earth orbit = the space station and many imaging satellites; Polar orbit = passes over the poles to scan the whole surface; Medium Earth orbit = GPS navigation satellites
Different orbits suit different jobs: geostationary for broadcasting, low orbit for stations, polar for mapping, and medium orbit for GPS.

Universal Gravitation

Build the sentenceLevel 2
19. Build the sentence describing what gravity is.
Answer: gravity is a force of attraction
Gravity is always an attractive force between masses; it never pushes them apart.
Choose all that applyLevel 2
20. Which factors change the strength of the gravitational force between two objects?
- The mass of the first objectcorrect
- The mass of the second objectcorrect
- The distance between the objectscorrect
- The colour of the objects
Gravitational force depends on both masses and the distance between them, not on colour.
Fact or fibLevel 2
21. Every object that has mass attracts every other object that has mass.
Answer: True
Gravity acts between all masses, though the pull is tiny for everyday objects.
Fill the blankLevel 2
22. As two objects move further apart, the gravitational force between them becomes ____.
- weakercorrect
- stronger
- unchanged
- negative
Gravitational force weakens with distance, so the further apart two masses are, the smaller the attraction.
Guess the numberLevel 3
23. The universal gravitational constant G is about 6.67 x 10^-11 N m^2/kg^2. Give just the number in front (the mantissa).
Answer: 6.67 x 10^-11 N m^2/kg^2
G is measured as 6.67 x 10^-11 N m^2/kg^2, one of the smallest constants in physics.
Match the pairsLevel 3
24. Match each symbol in F = G m1 m2 / r^2 to what it represents.
Answer: F = gravitational force between the masses; G = universal gravitational constant; m1 and m2 = the two interacting masses; r = distance between the mass centres
Newton's law links the force to the two masses, their separation r, and the constant G.

Weight and g

Fact or fibLevel 2
25. An object's weight depends on the strength of gravity where it is.
Answer: True
Because weight = mass x g, an object weighs more where gravity is stronger and less where it is weaker.
Fill the blankLevel 2
26. Weight is a force, so it is measured in ____.
- newtonscorrect
- kilograms
- metres
- seconds
Weight is a force and forces are measured in newtons (N).
Guess the numberLevel 2
27. On Earth, roughly what is the weight of a 10 kg object? (weight = mass x g, g about 9.8 m/s^2)
Answer: 98 N
Weight = 10 kg x 9.8 m/s^2 = 98 N.
Match the pairsLevel 2
28. Match each quantity to its correct unit.
Answer: Mass = kilogram; Weight = newton; Acceleration = metres per second squared; Time = second
Mass is in kilograms, weight (a force) in newtons, acceleration in metres per second squared, and time in seconds.
Multiple choiceLevel 2
29. How do you calculate the weight of an object?
- Multiply its mass by the strength of gravity (g)correct
- Divide its mass by the strength of gravity
- Add its mass to the strength of gravity
- Multiply its mass by its speed
Weight equals mass times g, so weight = mass x g.
Build the sentenceLevel 3
30. Arrange the words to state the equation for weight.
Answer: Weight equals mass times g
Weight = mass x g, where g is the gravitational field strength in N/kg.

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 17 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
Listen and choose
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sequence recall
Sort into groups
Spell it
Tap the pairs
True or false
Type the answer

Practise Gravity and Orbits

119 questions across 20 steps. Start with step one and crawl at your own pace.

Play this unit

Read about Gravity and Orbits

Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.

Why Satellites Stay in OrbitA satellite remains in orbit because gravity pulls it inward while its sideways motion carries it forward. Orbit is a continuous fall around Earth rather than an escape from gravity.July 26, 2026 · 5 min read

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