S4.8.4 For the adult
Newton's second law
An empty truck picks up speed quickly. A loaded truck with the same engine picks up speed slowly. Why?
What this chapter teaches
The resultant force on an object equals its mass times its acceleration, F = m × a, with force in newtons, mass in kilograms and acceleration in m/s². The same force gives a bigger mass a smaller acceleration.
Three questions to ask
There is no one right wording. Listen for the idea.
- A trolley of 3 kg has a resultant force of 12 N on it. How do you find its acceleration?
- Why must you work out the resultant force before using F = m × a?
- Why does a loaded truck speed up more slowly than an empty one with the same engine force?
After the chapter, the learner can
- Use force equals mass times acceleration in calculations
- Explain why a loaded truck speeds up more slowly than an empty one
What they copy into their notebook
Second law: resultant force = mass × acceleration, F = m × a. Use the resultant, and the mass in kg. Double the mass and the acceleration halves.