Motion and forces

Science understanding — Australian Curriculum v9.0, Year 10 Science.

Achievement focus

Students explain how Newton’s laws describe motion and apply them to predict motion of objects in a system.

---

AC9S10U05 — Newton’s laws of motion

Students learn to: investigate Newton’s laws of motion and quantitatively analyse the relationship between force, mass and acceleration of objects.

Core ideas

• First law (inertia): an object stays at rest or constant velocity unless a net external force acts.
• Second law: (net force, mass, acceleration); use SI units (N, kg, m/s²) for calculations.
• Third law: forces come in pairs—if A exerts a force on B, B exerts an equal and opposite force on A (on different bodies).

Learning checkpoints

1. A 50 kg rider on a kart experiences a net horizontal force of 200 N. What is the acceleration?
   Sample answer: .

2. A book sits on a table. Identify one Newton’s third-law pair involving the book.
   Sample answer: Earth pulls the book down (weight); the book pulls Earth up with an equal force. Or: table pushes book up; book pushes table down.