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4.3. Levers

How To Invent (Almost) Anything > 4. Applied Simple Science > 4.3. Levers

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Levers are simple devices that are used in many situations. We think that we understand them well, which makes them an excellent subject for invention: many inventors will ignore the ‘well-understood,’ preferring the choppier waters of new technology, leaving the simple and once over-fished territory for those who prefer profit to glamour.

At its most basic level, a lever is a trade-off between force and distance. Increase the length of the lever and less force is needed to move the target. As Archimedes said, ‘Give me a lever long enough and a prop strong enough and I can single-handedly move the world.’ But we can invent further beyond this basic variable.

Let us look closer at the humble door handle, round or flat lever, it does not matter. With some initial consideration, we can see that its function is to turn. All levers are carrying out a turning function. We use the handle to move a small part in the door: a lock or catch. To prevent the door rattling, the catch is pushed against the door frame parts. To hold the door firmly closed, we have friction, and the lever action is needed to overcome this friction.

So most of the time we want the friction between the catch and the frame, but when we open the door we want that friction to go away. When we have a door which is stuck we often push the door to reduce the friction between these parts. Here is an opportunity! Can you redesign the catch system so that less leverage is required?

For some levers it is not the friction which is the problem but the weight or mass of the object being moved. We are then using a lever to enable us to use a small force to move a large mass. A car jack operates like this, either with a long arm or using a screw action.

If you have ever used a poor quality jack you may have noticed that it bends near the connection point. This is because the greatest force is near the point of the fulcrum. Consider the shape of the arm/lever: usually they are of uniform shape and material along their length. As we are only applying a small force at the end we need only a light small section to our arm at this end. We need more and stronger material near the fulcrum.

Fig. 4.4 Improving the vehicle jack

Look around at lever systems–you may see these in the kitchen (grinders and graters will have some leverage somewhere) or in the garage (the door may have a lever system for operation) or anywhere. Now invent!

Other sections in this chapter:

• 4.1. Hinges
• 4.2. Bottle-tops
• 4.3. Levers
• 4.4. Nuts and Bolts
• 4.5. Knives
• 4.6. Invention 'So-what?'

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