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Work vs energy: what's the difference?

Highlighted from a real textbook passage. Explained by Clicked.

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University Course Reader · STEM

The work done by the crane on the load equals the force applied times the height through which it is raised.

The reader highlighted one word in a textbook passage. Clicked broke down the physics term “work” into plain English:

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Overview

Energy is what an object holds, stored in forms such as its motion, its height, its temperature or its chemistry. Work is energy that a force transfers to an object by moving it. The unit for both is the joule. Lift a 10 kg box onto a shelf 2 metres up and you do about 200 joules of work on the box. The box now holds those 200 joules as extra energy, stored in its height. Energy is what the box has; work is how it got there.
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Overview

Energy is what a thing has in the bank: speed, height, heat, chemistry, for a start. Work is energy a force moves in or out by shifting the thing. Hold a plank at the gym and you shake, sweat, and do zero work on the floor, which does not move. Your muscles burn energy every second; it all turns to heat, warming you and drifting into the gym air. Work needs something to move. Energy stays banked until a force moves it out, or it leaks away as heat. 😎

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Detail

Work is a transfer of energy, and energy is the quantity transferred. An object can hold energy in several forms: motion, height, temperature, chemistry, or shape, like a squeezed spring. A force transfers energy into or out of an object by moving it, and that transfer is the work. Only movement in the direction of the push or pull counts. Where the energy ends up depends on every force acting on the object, not just yours. A bike ride shows each piece. Press hard on the pedals while the brakes are on and you do no work, because nothing moves. Release the brakes and climb, and every turn of the pedals transfers energy: your legs push the pedals round, and what your muscles spend is stored as height. Ride back down without pedalling and gravity does the work instead, pulling you downhill and turning the height back into speed. Brake at the bottom and friction does the last of the work, slowing the wheels and turning your speed into heat in the brakes. Your muscular effort became height gained, the height became speed, and the speed became heat: energy was transferred at each step and held in between. Work is the transfer. Energy is what is held. Heat can also move energy, from a hot object to a colder one; a temperature difference drives that transfer, and no force is required.
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Detail

Energy is what a thing has, banked as speed, height, heat or chemistry, to name a few. Work is energy a force moves into a thing or out of it, and it only counts while the thing actually moves the way it is being pushed or pulled. Push a kid on a swing and every shove is work. Your hands push, the swing moves the way you pushed, and energy goes from your arms into the swing and the kid. At the top of the arc the kid is briefly still and holds that energy as height, and on the way down it turns into speed. Now hold the swing still at the top while they sort out their shoelace. You are pushing as hard as gravity pulls, and your arms know about it, but you are doing zero work on the swing, because it is not moving. The energy you burn holding it turns to heat, which your body sheds through your skin and your breath. Let go and gravity takes over: it pulls the kid down the arc, the kid moves the way it pulls, and gravity does the work this time. Work is always some named force moving some named thing. Energy is what the thing holds at any moment, however it got there. 😎

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Analogy

Wind up a clockwork toy and you are doing work on it: you push the key round, the key turns, and energy is transferred out of your muscles and into the spring. Once you stop winding, that energy sits in the coiled spring, and it stays there for as long as the toy is still. Let the toy go and the spring does work in its turn: it pushes the wheels round, the wheels move the way they are pushed, and the stored energy is transferred on into motion. Squeeze the key without turning it and you transfer nothing, however hard you grip, because work needs movement, not just effort. Energy is what the spring holds. Work is each transfer in and out of it.
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Analogy

Roll a bowling ball and all the work happens in the swing: your arm pulls the ball through, the ball moves with the pull, and energy is transferred in. The moment the ball leaves your hand, the transfer is over. The lean, the wince, the pleading as it drifts towards the gutter transfer nothing, because you are no longer applying a force that moves it. The ball carries the energy you gave it down the lane and hands it to the pins, and that handover is work again, ball on pins this time. Energy is what the ball carries between your hand and the pins. Work happens only at the two ends. 😎
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Formal definition — The same term, explained the usual way

Energy is a conserved scalar quantity, measured in joules (J), that a system possesses by virtue of its motion (kinetic energy), position or configuration (potential energy), temperature (thermal energy), chemical bonding, and other forms; it can be transferred between systems but neither created nor destroyed. Work is energy transferred to or from a body by a force acting through a displacement, equal to the component of the force along the displacement multiplied by the distance moved (W = F d cos θ); it is zero if the point of application does not move or moves perpendicular to the force, and negative if the force opposes the motion, as with friction. Work and heat are the two modes of energy transfer; the net work done on a body by all forces equals its change in kinetic energy (the work-energy theorem).

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