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DENJIRO: Here's a unique type of bow. It's called a compound bow and is often used in the Paralympics. Let's try shooting it first. The difference between this and a regular bow is the pulleys attached to the two ends of the bow. This pulley allows the user to draw the bow with little force.
I'm going to pull the bowstring with a spring scale. At first, you need a force of about 5 kg to pull the string. But let me keep pulling. The number has now dropped to about 2.5 kg. With a compound bow, less force is required after a certain point. Therefore, people with not much strength can use it and can aim better as their hands will not shake as much.
The key is this pulley. It actually works as a wheel and axle. Let me explain using this model right here. One weight is attached to the outer disk, and two are attached to the inner disk, which has half the radius. The weights are balanced right now. This is the mechanism behind the wheel and axle. The longer the distance from the axle, the less force you need to spin it. In this case, the larger disk is able to spin with half the power of the smaller disk. This mechanism is applied to the compound bow.
This is a model that represents the wheel and axle of the compound bow. We have the string that represents the bowstring, and there is an axle in the middle. Right now, it's in the same position as if the bowstring weren't being pulled, so the string is close to the axle. This means a greater force is necessary. As we pull more, the distance between the axle and string increases, and less power is required to support the bowstring. This mechanism allows the bow to maintain the tension needed to fire the arrow but without too much force.
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