Physics (university) · Part 02
Newton's laws and forces
How pushes and pulls change motion, from friction to inclined planes.
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- Newton's first lawAn object keeps its velocity (including staying still) unless a net force acts on it.
- Net forceThe vector sum of every force on an object. It decides whether the object speeds up, slows down, turns or stays steady.
- Newton's second lawNet force equals mass times acceleration (F = ma). The same push gives a small mass more acceleration.
- Newton's third lawWhen object A pushes on object B, B pushes back on A with an equal and opposite force. The two forces act on different objects.
- WeightThe pull of gravity on an object, found with W = mg. Mass stays the same everywhere, weight does not.
- Normal forceThe push a surface gives back, at right angles to it, when something presses on it. It changes with acceleration.
- FrictionA force along a surface that resists sliding. Its largest value is the coefficient of friction times the normal force.
- Free-body diagramA sketch of one object with arrows for every force acting on it. It turns a messy problem into F = ma.
- TensionThe pulling force along a rope or string. An ideal light rope has the same tension all along it.
- Inclined planeA ramp problem. Gravity splits into a part along the slope and a part pressing into it.