Overview
What you’ll learn
- Distinguish contact forces, such as friction, from non-contact forces, such as gravity and magnetism.
- Describe effects of forces: a change in motion, a turning effect, a change in shape or size, and pressure.
- State that force is measured in newtons, compare weight and mass, and use pressure = force ÷ area.
- State that energy is measured in joules, can be transferred or converted, and is conserved.
- Describe energy sources and one environmental effect of using them.
In 30 seconds
- 1A force is a push or a pull, measured in newtons (N) with a force meter.
- 2Contact forces need touching, such as friction. Non-contact forces act at a distance, such as gravity and magnetism.
- 3Forces can start or stop motion, turn an object, change its shape, or produce pressure. Pressure = force ÷ area.
- 4Mass (kg) is the amount of matter. Weight (N) is the gravitational force on that matter. They are not the same quantity.
- 5Energy is measured in joules (J). It can be transferred or converted from one form to another. It is not created or destroyed.
- 6Energy sources such as fossil fuels, the Sun, wind and moving water have benefits and environmental costs.
Notes · 1 of 5
Contact and non-contact forces
Some forces need contact. Gravity and magnetism do not.
- Contact
- Friction, the push of your hand, and the support from the floor all need objects to touch.
- Non-contact
- Gravity pulls you to Earth without you touching the planet. A magnet pulls iron without touching it.
The SI unit of force is the newton (N). A force meter, sometimes called a spring balance, measures it. A reading without the unit is incomplete.
Notes · 2 of 5
What forces do
A force can change motion, produce a turning effect, or change shape. It can also be spread over an area as pressure.
- Motion: a force can start, stop, speed up, slow down or change the direction of an object.
- Turning: a spanner turns a nut. A lever helps open a tin. The force has a turning effect.
- Shape and size: squeezing a spring or clay changes its shape. The force is doing that.
- Pressure: the same force on a smaller area gives a higher pressure. A sharp knife and a stiletto heel are everyday examples.
Pressure = force ÷ area. A 40 N force on an area of 2 cm² gives a pressure of 20 N/cm². The same force on 8 cm² gives 5 N/cm². High pressure is useful for cutting. Low pressure, from a large area, stops you sinking, which is why a wide bag strap is more comfortable than a thin string.
Notes · 3 of 5
Weight and mass
Mass stays with the object. Weight is a force and depends on gravity.
| Property | Mass | Weight |
|---|---|---|
| What it is | Amount of matter | Gravitational force on that matter |
| Unit | kilogram (kg) | newton (N) |
| Instrument | Electronic balance (compares mass) | Force meter |
| If you could go to the Moon | Unchanged | Smaller, because gravity is weaker |
On Earth a mass of 1 kg has a weight of about 10 N. So a 4 kg school bag weighs about 40 N here. The bag’s mass is still 4 kg. Say “weighs 40 N” or “has a mass of 4 kg”, and do not mix the units.
Notes · 4 of 5
Energy transfer and conservation
Forces and fuels move energy from one place or form to another. The total is not created or destroyed.
The SI unit of energy is the joule (J). Work is done when a force moves an object in the direction of the force. That is one way energy is transferred. Lifting a bag gives it gravitational potential energy. A moving bicycle has kinetic energy. A stretched spring has elastic potential energy.
Energy can be converted from one form to another: chemical energy in food to kinetic energy when you run, or electrical energy to light and heat in a lamp. Energy is conserved. It is not created or destroyed. In real machines some energy is transferred to the surroundings as heat, so it is not all in the form you wanted. It has not vanished.
Notes · 5 of 5
Energy sources and the environment
Every source has a use and an impact. Name both.
| Source | A use | An environmental point |
|---|---|---|
| Fossil fuels | Electricity, transport | Burning them adds carbon dioxide and uses a finite store |
| Sun (solar) | Electricity, heating water | No fuel is burnt while the panel works; panels need manufacture and space |
| Moving water / wind | Electricity | No fuel is burnt; dams and turbines change habitats |
| Nuclear | Electricity | A large output from a small mass of fuel; waste and accident risk |
Forces in nature can also be destructive: earthquakes, tsunamis, volcanic eruptions and tropical cyclones transfer enormous amounts of energy. Curiosity about those events is part of this topic. The useful exam move is still to name the force or the energy change in the situation you are given.
Revise
Key terms
The words examiners expect you to use precisely.
- Force
- A push or a pull. The unit is the newton (N).
- Contact force
- A force that acts only when objects touch, such as friction.
- Non-contact force
- A force that acts at a distance, such as gravity or magnetism.
- Friction
- A contact force that opposes sliding between surfaces.
- Weight
- The gravitational force on an object, measured in newtons.
- Mass
- The amount of matter in an object, measured in kilograms. It does not change if gravity changes.
Show 3 more key termsShow fewer key terms
- Pressure
- Force spread over an area. Pressure = force ÷ area.
- Energy
- The capacity to make things happen. The unit is the joule. It is conserved when it is transferred or converted.
- Kinetic energy
- The energy an object has because it is moving.
Revise
Common mistakes
Where students most often lose marks in this chapter — and what to do instead.
Mistake: Giving weight in kilograms.
The kilogram is the unit of mass. Weight is a force.
Instead: Mass in kg. Weight in N. On Earth, weight in newtons is about ten times the mass in kilograms.
Mistake: Calling gravity a contact force.
You do not have to touch Earth to be pulled by it.
Instead: Gravity and magnetism are non-contact forces. Friction is a contact force.
Show 4 more mistakesShow fewer mistakes
Mistake: Saying a larger force always means a larger pressure.
Pressure also depends on area.
Instead: Pressure = force ÷ area. A smaller area raises the pressure.
Mistake: Saying energy is used up and disappears.
The conservation statement forbids that.
Instead: Energy is transferred or converted. Name the new form or the surroundings.
Mistake: Treating every metal-and-magnet example as a contact force.
The magnet pulls before the objects touch.
Instead: Magnetic force is non-contact. Once the objects touch, contact forces appear as well.
Mistake: Forgetting the unit on a pressure calculation.
The unit shows whether you divided newtons by cm² or by m².
Instead: Write N/cm² or N/m² to match the area you used. Do not mix the area units.
Check yourself
Quick quiz
10 questions with instant explanations. About 5 minutes.
Question 1 of 3
- Question 1: current question
- Question 2: not answered
- Question 3: not answered
Classify forces
Which is a non-contact force?
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Practise
Topical questions
Exam-style practice in three tiers, from recall to data questions.
- 5Foundation
- 5Standard
- 5Challenging
15 questions worth 41 marks, each with a model answer, mark scheme and examiner tips.
Practise topical questionsExam practice
Practice paper
A 30-mark paper set out like a school paper, with a separate mark scheme. Give yourself 40 min.
Question paper
Chapter 1 Practice Paper
30 marks · 40 min · 6 pages
10 multiple-choice questions and structured questions with answer lines. Chapter 1.
Mark scheme
PROChapter 1 Practice Paper — mark scheme
Answers · Marking points · 3 pages
Model answers with a mark for each creditworthy point — for marking at home or in class.
Where this chapter is tested
Each school sets its own scope — check your assessment outline.
Questions
Frequently asked questions
What is the difference between mass and weight in Sec 2 Science?
Mass is the amount of matter, in kilograms, and it does not change if gravity changes. Weight is the gravitational force on that matter, in newtons. On Earth, weight is about 10 N for each kilogram.
How do you calculate pressure?
Pressure = force ÷ area. Use newtons for the force and keep the area unit consistent, for example N/cm² or N/m². A smaller area gives a higher pressure for the same force.
What is a non-contact force?
A force that acts without the objects touching. Gravity and magnetism are the examples to learn. Friction is a contact force.
Is energy destroyed when a ball stops?
No. The kinetic energy is transferred, often as heat to the ball and the ground because of friction. Energy can change form. It is not created or destroyed.
Is forces and energy in the Sec 2 EOY?
Most schools that follow the usual G2/G3 scheme teach this chapter in Sec 2 and include it in the Sec 2 end-of-year paper. A few schools move a topic across the two years, so check your school’s assessment outline.
Up next
Chapter 2: Transfer of Heat Energy and its Effects