Normal Force: Why Fɴ = mg·cos θ on an Incline

Normal Force: The Support Force That Isn't Always Equal to Weight

The normal force is the perpendicular support a surface exerts, and it equals mg only when there is no perpendicular acceleration. This simulation lets students drag the incline angle and watch the normal force fall from mg to mg·cosθ in real time. Built to fix the common misconception that the normal force always equals weight, and to show why the normal force is not the same as gravity.

Drag the incline angle and watch the normal-force arrow shrink. On a flat surface it equals the full weight mg — but as the slope steepens, it drops to mg·cosθ. Watch the live graph track the normal force against the angle. Takeaway: the normal force is whatever the surface must supply, and it equals weight only when the surface is flat.

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