The crossbow is a combination of an archery bow and a rifle. The standard archer’s bow it uses a string to launch ammunition. However, like a rifle, it has a trigger that releases the string.
Advantages of a Crossbow
The nice feature of the crossbow when compared to other bows is there is less physical strength needed to draw the bow as compared to a traditional bow. The crossbow user can draw the string, cock it, and leave the string while taking aim. More traditional bows require the archer to hold the bow at full draw while aiming. In addition, to draw a crossbow requires the use of the archer’s buttock and thigh muscles. These muscles are much stronger than the arm and chest muscles required of a standard bow user.
The crossbow of today is made of strong lightweight materials. The bow is simply a spring. If you compress a spring or pull a spring from either end it stores potential energy that is released as kinetic energy when the spring is released and returns to its normal shape.
The same thing happens to a crossbow. When you draw the bow, the limbs or tips move closer to the archer. When the string is let go the bow returns to its standard shape. The movement of the bow back to its original shape is what launches the projectile.
The amount of energy in a bow depends on its draw weight and draw length. The draw weight is the strength needed to pull the bowstring back. The draw length is the distance between the string at rest and the string fully pulled back. A bow can hold energy equal to the draw weight times the draw length divided by two. In other words, the power of a bow depends on how much strength it takes to pull back the string of the bow and how far back you can pull it. Bow makers express this strength in terms of the bow’s energy measured in joules and the arrow’s speed in feet per second.
Factors that affect the draw weight and draw length
The size of the bow can change a bow’s power. A longbow is more powerful than a short bow. The shape of the bow affects speed of the projectile. For example, recurve bows have bows that curve away from the archer and this shortens the bracing height. As a result extra momentum is forced onto the projectile. The composition of the bow can also affect is power. A bow’s tensile strength and density determine not only the amount of energy it holds but also how quickly and exactly it can return to its original shape. Today’s bows use different materials in different parts of the bow to better serve that particular part or function of the part.
As you can see the crossbow works like a spring. As the spring is compressed, or the bowstring drawn back energy get stored as potential energy. When the trigger of the crossbow is released, like the spring, the crossbow will return to its original resting state dispensing the potential energy it stored as kinetic energy. This kinetic energy is responsible for launching the ammunition at high velocity.
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