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Friction force; tipping and sliding of block

Short answer

Friction force is the resisting force along contact surfaces opposing relative motion, with limiting value μN. For a block of weight W, base width b, pushed at height a: sliding occurs if P > μW; tipping about the toe occurs if P > Wb/(2a). The smaller P decides the first failure mode.

Define friction force and explain condition of tipping and sliding of a block.

Friction force

Friction force is the resisting force that acts along the common tangent of two surfaces in contact and opposes the relative motion, or the tendency of motion, of one surface over the other. Its maximum (limiting) value is F = μN, where N is the normal reaction.

Sliding and tipping of a block

Take a block of weight W, base width b, acted on by a horizontal force P at height a above the base, with coefficient of friction μ.

  • Sliding: the block slides when P exceeds the limiting friction: P > μW (since N = W).
  • Tipping: the block tips about its lower toe when the overturning moment exceeds the restoring moment: P a > W b/2, i.e. P > Wb/(2a).

The smaller of the two values of P decides what happens first: if μW < Wb/(2a) the block slides; if Wb/(2a) < μW it tips. When tipping starts, the normal reaction moves to the toe of the block.

✓ Answer checked by Claude Opus 5.5 (high effort)

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