Physics (school) · Part 02
Forces and Newton's laws
How forces change motion, from weight and friction to the three laws.
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- ForceA push or a pull, measured in newtons (N). It can change speed, direction or shape.
- Resultant forceThe single force that has the same effect as all the forces on an object added together, taking direction into account.
- Newton's first lawAn object stays still or keeps moving at a steady speed in a straight line unless a resultant force acts on it.
- Newton's second lawResultant force = mass x acceleration (F = ma). A bigger force gives a bigger acceleration. A bigger mass gives a smaller one.
- Newton's third lawWhen object A pushes on object B, B pushes back on A with an equal force in the opposite direction.
- Weight and massMass is the amount of matter in an object, in kg. Weight is the pull of gravity on it, in N. Weight = mass x gravitational field strength (W = mg).
- Friction and dragFriction is a force that opposes sliding between two surfaces. Drag is the force that opposes movement through air or water.
- Terminal velocityThe steady top speed reached when drag grows until it equals the driving force, so the resultant force is zero.