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Year 9

Gravitational force and weight

I can describe and apply the relationship between mass and gravitational force.

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New
New
Year 9

Gravitational force and weight

I can describe and apply the relationship between mass and gravitational force.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. The mass of an object is measured in kilograms.
  2. A force of about 10 N is needed to lift 1 kg on Earth.
  3. On Earth a 1 kg mass pushes down on a surface with a force of about 10 N.
  4. There are 1000 g in 1 kg.
  5. Gravitational force, W = m x g

Common misconception

Pupils often mix up the terms for weight and mass and use weight when they mean mass and vice versa.

Teach pupils that a force lifts objects against the pull of gravity before introducing the term weight.

Keywords

  • Gravitational force - The force that acts on an object inside a gravitational field.

  • Mass - The amount of matter (material) in an object.

  • Gravitational field strength - The force per kilogram caused by a gravitational field.

  • Newton - The unit for force.

  • Newtons per kilogram - The unit for gravitational field strength.

Allow pupils to lift objects with different masses, getting them to compare the sizes and weights. Discuss weight as the force the object is putting on the pupils hands when they lift something.
Teacher tip

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Starter quiz

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6 Questions

Q1.
How can a force acting on an object be shown on a diagram?
An arrow pointing to where the force is acting on the object.
Correct answer: An arrow starting on the object and pointing to the direction the force acts.
A straight line joining the object to the force.
Q2.
Which of these forces pulls objects towards the centre of Earth?
tension
normal reaction force
Correct answer: gravitational force
electric force
magnetic force
Q3.
How should a force arrow for the gravitational force acting on a football be drawn?
Correct answer: Starting in the centre of the football.
Starting in the bottom of the football.
Starting in the top of the football.
Correct answer: Pointing downwards.
Pointing upwards.
Q4.
What property does this top pan balance measure?
An image in a quiz
force in grams
weight in grams
Correct answer: mass in grams
mass in newtons
Q5.
The figure shows a hand holding a small metal block. The metal block is not moving. Which statements are correct?
An image in a quiz
There are no forces acting on the metal block.
Correct answer: There is no resultant force acting on the metal block.
Correct answer: There is an upwards support force acting on the metal block.
Correct answer: There is a gravitational force is acting on the metal block.
The metal block has no mass.
Q6.
An astronaut is walking on the Moon carrying a hammer. What will happen to the hammer if they let go of it?
An image in a quiz
The hammer will float off upwards, getting faster and faster.
The hammer will float exactly where it was released.
The hammer will fall towards the Moon's surface at a constant speed.
Correct answer: The hammer will fall towards the Moon's surface, speeding up as it falls.

Exit quiz

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6 Questions

Q1.
Match the key words to their definitions:
Correct Answer:gravitational force,A force that pulls objects towards the centre of planets.

A force that pulls objects towards the centre of planets.

Correct Answer:mass,The amount of material (matter) in something.

The amount of material (matter) in something.

Correct Answer:gravitational field strength,The force on each kilogram due to gravity.

The force on each kilogram due to gravity.

Correct Answer:newton,The unit used for force.

The unit used for force.

Correct Answer:newtons per kilogram,The unit for gravitational field strength.

The unit for gravitational field strength.

Q2.
Starting with the smallest, sort these in order of mass.
1 - 0.2 g
2 - 25 g
3 - 200 g
4 - 0.25 kg
5 - 2 kg
6 - 20 kg
Q3.
An astronaut takes a flag pole from Earth to the Moon with them. Which of the following are true?
An image in a quiz
Correct answer: The mass of the flag pole stays the same.
The mass of the flag pole decreases.
The mass of the flag pole increases.
The weight of the flag pole stays the same.
Correct answer: The weight of the flag pole decreases.
Q4.
An alien weighs themselves on the surface of some of the moons in our solar system. Starting with the smallest, list the locations into the order of the weight recorded.
1 - Umbriel (g = 0.20 N/kg)
2 - Ariel (g = 0.27 N/kg)
3 - Oberon (g = 0.34 N/kg)
4 - Triton (g = 0.77 N/kg)
5 - Callisto (g = 1.2 N/kg)
6 - Ganymede (g = 1.4 N/kg)
7 - Io (g = 1.8 N/kg)
Q5.
A space probe has a mass of 954 kg and is being sent to land on the moon Europa, which has a gravitational field strength of 1.31 N/kg. How much will it weigh on Europa?
728 N
955 N
953 N
1.25 N
Correct answer: 1.25 kN
Q6.
An astronaut with mass 652 kg lives on Mars. They weigh themselves and find that they weigh 2420 N. What is the gravitational field strength?
Correct answer: 3.71 N/kg
1.58 N/kg
0.27 N/kg
8.94 N/kg
0.37 N/kg