Normal force
The push a surface gives back, at right angles to it, when something presses on it. It changes with acceleration.
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Analogy
The floor pushing up on your feet.
Example
N - mg = maN = 70(9.8 + 2)N = 826 N
In practice
In an elevator accelerating up at 2 m/s squared, a 70 kg rider feels 826 N from the floor.
Practice
Flashcards
- What is the formula for maximum static friction?f max = (coefficient of friction) x (normal force).
Questions people ask
Is the normal force always equal to weight?
No. It equals weight only when the surface is flat and nothing else pushes vertically or accelerates the object. On a slope it is smaller, and in an accelerating elevator it changes. Always find it from F = ma along the perpendicular direction.
Why is it called normal?
In maths, normal means at right angles. The normal force is the contact force that acts perpendicular to the surface. It is a push, never a pull, and it stops objects from passing through the surface. It has nothing to do with being ordinary.