What Is a Force? Contact and Non-Contact
You'll be able to classify forces as contact or non-contact.
In 2022, Kelsey-Lee Barber hurled a javelin 64.91 m to win gold for Australia, every centimetre shaped by contact and non-contact forces acting at once.
Printable Worksheets
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Q1 · Push a door and pull a drawer open. What's the difference between pushing and pulling?
Q2 · Can one object affect another without touching it? Give an example from your life.
● Know
- The definition of a force and its unit (Newton)
- The difference between contact and non-contact forces
- Examples of each type of force in everyday life
● Understand
- Why forces are represented as arrows (vectors)
- How multiple forces can act on one object at the same time
- That all forces in daily life come from just 4 fundamental forces
● Can do
- Classify forces as contact or non-contact
- Draw a simple force arrow diagram with labels
- Identify forces acting on an Australian everyday object
When you kick a ball, something invisible happens in the fraction of a second your foot touches it. That invisible thing, a force, changes the ball's speed and direction. Forces are pushes or pulls.
Saying "I kicked it hard" is not enough for science, because two separate pieces of information decide what happens to the ball. The first is magnitude, how big the force is, measured in Newtons (N). The second is direction, which way the force acts. Change either one and the ball ends up somewhere different: the same size kick aimed at the side of the ball sends it sideways rather than forward, and a gentler kick in the same direction sends it a shorter distance. Because you need both pieces of information before you can say what a force will do, a force is called a vector.
That is also why forces are drawn as arrows instead of written as numbers. An arrow carries both pieces of information at once. How long you draw it stands for the magnitude, so a longer arrow means a bigger force, and where it points stands for the direction. This matters more than it first looks: two arrows drawn on the same object can be compared at a glance, so you can see which force is winning without doing any arithmetic. That single trick is the whole reason force diagrams exist, and you will use it in every lesson from here on.
What a force actually does is change motion, and that change shows up in four ways. A force can start a stationary object moving, which is what happens when you push a still ball. It can stop something that was already moving, which is what the brakes on a bicycle do. It can change the direction of something without making it faster or slower, which is what turning a steering wheel does to a car. And it can change an object's shape, which is what your hand does when it squashes a soft drink can. Look at what those four have in common: in each one, something about the object was different afterwards. That is the test to apply when you are unsure whether a force acted at all, because if nothing about the object changed, no unbalanced force was acting on it.
Force is measured in Newtons (N), named after Sir Isaac Newton. A newton is a small amount of force: holding a small apple up against gravity takes about 1 N, and carrying a school bag full of books takes somewhere around 50 to 80 N. Those two numbers are worth keeping in your head, because they give you something to test an answer against. If a calculation tells you that shifting a loaded wheelie bin needs 2 N, the number is far too small to be right, and knowing that is often faster than checking the working.
Text description
- Contact forces: objects must touch. Push (hands touching), friction (surfaces touching), pull (rope touching), normal (floor touching).
- Non-contact forces: no touching needed. Gravity and magnetism act at a distance; electrostatic force (static charge) acts at a distance.
Forces split into two families, and the boundary between them is decided by a single question: does the thing doing the pushing have to be touching the thing being pushed? If the answer is yes, remove the contact and the force disappears instantly. If the answer is no, the force reaches across a gap and keeps acting with nothing in between.
Try that question on a case that catches people out. A yacht's sail is pushed along by the wind, so is that a contact force or a non-contact force? It feels like a non-contact force, because nothing solid is visibly touching the sail. But air is made of matter, and the air molecules are hitting the sail, so the wind is a contact force. Now take the balloon that sticks to a wall after you rub it on your jumper. Slide a sheet of paper between the balloon and the wall and the balloon still holds. Nothing has to touch for that force to work, so it is a non-contact force. The test is not "can I see what is touching?" but "is anything touching at all?"
Contact forces only work when objects are physically touching:
- Friction opposes sliding motion between surfaces (e.g. your shoe gripping the floor)
- Tension pulling force along a rope, string or wire (e.g. a tug-of-war rope)
- Normal force the surface pushes back when you press on it (the chair pushing up on you)
- Applied force a direct push or pull you apply with your hands
Non-contact forces act between objects that are NOT touching:
- Gravity Earth pulls every object downward (the Moon is pulled by Earth's gravity even though they're 384,000 km apart)
- Magnetism magnets attract or repel other magnets and magnetic materials from a distance
- Electrostatic force static electricity on a balloon attracts small pieces of paper without touching
Notice that the two families are not two separate worlds. A surfer at Bondi Beach has forces from both acting at the same instant: gravity pulls down on the board and rider without touching them, while the water pushes up on the board and drags backward against it, and both of those need contact with the water. Most real situations are like this. Asking "is this a contact or a non-contact force?" is a question about one force at a time, never about the whole scene, and getting into the habit of naming forces one at a time is what stops a force diagram becoming a guess.
Australian context: none of these forces on the surfer are visible. That is exactly why force diagrams are worth drawing: an arrow shows the size and direction of something you could never photograph.
This card is background, not a Stage 4 requirement. Nothing you are assessed on in this unit depends on the four names below, and you can skip to the activities without losing any marks. It is here because it answers a question the last card leaves open: if a contact force needs objects to touch, what is actually doing the pushing when they do?
The answer is that every force in the universe traces back to just four fundamental forces. When your book presses on the desk, the atoms in the book never truly touch the atoms in the desk. Each atom is surrounded by a cloud of electrons, and electrons carry negative charge, so the two clouds push each other apart before the atoms can meet. What you feel as a solid surface is that electrical push, which means the normal force from the desk is really an electromagnetic force wearing a different name. The same is true of friction and tension. So "contact" is a description of how a force looks from the outside, not of what is happening underneath.
| Fundamental force | What it does | Everyday example |
|---|---|---|
| Gravity | Attraction between any two objects with mass | You staying on the ground; the Moon orbiting Earth |
| Electromagnetic | Forces between electrically charged particles, includes magnetism, light, and ALL contact forces at the atomic level | Magnets; static electricity; friction at the atomic scale |
| Strong nuclear | Holds the protons and neutrons together inside an atom's nucleus | Nuclear power; the Sun's energy |
| Weak nuclear | Responsible for radioactive decay | Radioactive materials; carbon dating |
For Year 7 science, only the first two are worth carrying with you. Gravity and the electromagnetic force explain every force you will meet in this unit, and the two nuclear forces never reach outside an atomic nucleus, which is why you never notice them. Keep the level straight: friction, tension and the normal force are the names Stage 4 asks you to use, and "electromagnetic" is the deeper reason they exist rather than a replacement for them.
A book sits still on a table. List all the forces you think are acting on the book. Are they contact or non-contact? What do you predict is special about how these forces compare to each other?
How close was your prediction?
Well done, you identified the forces and noticed they balance out.
Key insight: even still objects have forces acting on them, they just cancel out.
Below are 10 everyday forces. For each one, write whether it is a contact force (C) or non-contact force (NC), then name the specific force type.
| # | Situation | C or NC? | Force type |
|---|---|---|---|
| 1 | A rope pulling a water-skier | ||
| 2 | Earth pulling the Moon toward it | ||
| 3 | Your shoe gripping the footpath | ||
| 4 | A compass needle turning to face north | ||
| 5 | A chair pushing up on you as you sit | ||
| 6 | Static on a jumper attracting lint | ||
| 7 | A swimmer pushing off the pool wall | ||
| 8 | The Sun pulling Earth in its orbit | ||
| 9 | Air resistance slowing a falling leaf | ||
| 10 | A crane cable holding a load |
Draw a labelled force diagram of a person sitting in a chair. You should include:
- The person shown as a simple box or stick figure
- An arrow for gravity (label it with "Gravity" and a downward arrow)
- An arrow for the normal force from the chair (label it with "Normal force" and an upward arrow)
- Make both arrows approximately the same length to show they are balanced
After drawing (in your book or on paper), answer these questions here:
Q1. Name two contact forces and the non-contact force acting on a skydiver before and after the parachute opens. (2 marks)
Q2. Explain why forces are drawn as arrows in science. What does the length and direction of the arrow tell you? (3 marks)
Q3. A ball is sitting still on a table. Name all the forces acting on it and explain why it doesn't move. (3 marks)
Answers
▾MCQ 1
B A force is a push or pull. Weight is the effect of gravity, speed is motion, and stored energy is potential energy, none of these define what a force is.
MCQ 2
C Gravity acts between objects without them touching. Friction, tension and normal force all require direct contact between objects.
MCQ 3
B Arrow length represents magnitude (how big the force is). Length does not indicate speed, mass or direction change, the arrowhead shows direction.
MCQ 4
C A fridge magnet uses magnetic force, which is a non-contact force. The magnet doesn't grip or tie, it attracts at a distance through its magnetic field.
MCQ 5
D Friction is a contact force, it only acts when surfaces are touching. Gravity, magnetism and electrostatic attraction are all non-contact forces.
Short Answer 1
Model answer: Contact forces: air resistance/drag (fluid friction) and tension from the parachute straps. Non-contact forces: gravity (pulling the skydiver down throughout). Note: gravity acts before and after the parachute opens; air resistance increases dramatically after the parachute opens, creating a large upward drag force.
Short Answer 2
Model answer: Forces are drawn as arrows because forces are vectors, they have both magnitude (size) and direction. The length of the arrow represents the magnitude of the force (longer arrow = bigger force). The direction the arrowhead points shows which way the force acts (e.g., downward for gravity, upward for normal force). Using arrows lets scientists show multiple forces on the same object clearly and to scale.
Short Answer 3
Model answer: Two forces act on the ball: (1) gravity, a non-contact force pulling the ball downward, and (2) the normal force from the table, a contact force pushing the ball upward. The ball doesn't move because these two forces are equal in magnitude and opposite in direction, so they cancel each other out. The net (total) force is zero, so there is no change in the ball's motion, it stays still.
At the start of this lesson you saw the hook: a fridge magnet holding a note against a metal fridge without glue or string. Now you know what's going on, it's a non-contact magnetic force acting across a tiny gap!
How does your new understanding of contact vs non-contact forces compare to what you first thought? Name at least two other non-contact forces and explain what they all have in common.
- A force is a push or pull measured in Newtons (N). It is a vector, it has magnitude and direction, shown by an arrow.
- Contact forces (friction, tension, normal, applied) need objects to touch; non-contact forces (gravity, magnetism, electrostatic) act at a distance.
- All forces come from 4 fundamental forces, for everyday science, gravity and electromagnetic force explain almost everything.