Forces and Motion
MYP Year 3 Sciences: Forces and Motion
This topic is really one idea wearing six different outfits: what does the net force do to the object's motion? Every question — whether it's a box on carpet, a toy car on sandpaper, or a graph of a cyclist's journey — is testing whether you can find the net force (or read it off a graph) and then correctly predict speeding up, slowing down, staying at constant velocity, or staying still. Get that reasoning chain solid and every subtopic below becomes the same three steps repeated.
Overview — the shape of this topic
Why these six subtopics are really one argument
Forces don't need to be 'big' or 'obvious' to matter — a book sitting still on a table has real forces acting on it (weight and normal force), they're just balanced. The entire unit builds toward one skill: identify every force acting, work out the net (resultant) force, then use that net force to explain or predict the motion. Motion graphs and speed/velocity/acceleration give you the language to describe motion; force diagrams, friction, and balanced/unbalanced forces give you the reasoning to explain why it happens.
- Friction and drag are the forces most exam questions hide inside real contexts — carpets, brake pads, wet roads.
- Distance-time graphs turn motion into a shape you can read: gradient is speed, and the shape of the line tells the whole story.
- Speed, velocity and acceleration are the vocabulary for how fast and how the speed is changing — mixing these up is the single most common vocabulary error in this unit.
- Force diagrams are the working-out step: draw every force as an arrow, then combine them to get the net force.
- Knowing the types of forces (contact vs non-contact) lets you correctly identify what's even acting before you can diagram it.
- Balanced and unbalanced forces is the payoff — the rule that connects net force directly to constant velocity vs acceleration.
The shape of the chapter
Command terms this topic actually tests
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| Identify | Give a short, precise answer — a direction, a name, a value — with no explanation required. | AO1 | 1 mark for the correct short answer alone; adding an explanation neither helps nor hurts. |
| Describe | State what is happening or the pattern shown, using specific details from the data, graph or diagram. | AO1/AO2 | Marks awarded per distinct feature named (e.g. 'increases, then levels off'), not for one vague general comment. |
| Explain | Give reasons — the 'why' — linking a cause to its effect (e.g. link friction size to net force to speed change). | AO2 | The causal link itself carries the mark; stating the fact alone without the link earns 0. |
| Calculate | Show working using the correct formula and give a final numerical answer with the correct unit. | AO2 | A method mark is often available for correct substitution even if the final arithmetic is wrong; missing units can cost the final mark. |
| Analyse | Break down data or a relationship and comment on pattern, consistency, or significance — go beyond describing to interpreting. | AO3 | Requires comparing actual values against an established trend, not just repeating the numbers given. |
Key point
Overview