What is Work of a constant force? — Physics

Definition 17.1 High School Physics · Chapter 17 — Work of a Force

A constant force $\vect F$ applied to an object moving along a straight segment from $A$ to $B$ does the work

W_{AB}(\vect F) = F \times AB \times \cos\theta ,

where $F$ is the magnitude of the force (in $\mathrm{N}$ ), $AB$ the length of the displacement (in $\mathrm{m}$ ) and $\theta$ the angle between $\vect F$ and $\vect{AB}$ . Work is measured in joules ( $\mathrm{J}$ ): one joule is the work of a one-newton force along one metre of its own direction.

Only the projection F of the force on the displacement works: W_AB( F) = F × AB ×. — Only the projection $F\cos\theta$ of the force on the displacement works: $W_{AB}(\vect F) = F \times AB \times \cos\theta$ .

Examples

Example 17.3 (Suitcase on a leash)

A traveller drags a suitcase $300\,\mathrm{m}$ across a terminal, the strap pulled with $F = 40\,\mathrm{N}$ at $\theta = 50{}^{\circ}$ to the floor: $W = 40 \times 300 \times \cos50{}^{\circ} \approx 7.7\,\mathrm{kJ}$ . Pulled flat ( $\theta = 0$ ) the same force would deliver $12\,\mathrm{kJ}$ : a third of the pull lifts nothing.

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Examples

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