Physics of Archery
Energy, Work and Power
Work can be described as the amount of force exerted over a specific distance (W=F∆d). It can also be characterized by a change in energy (∆E), which can be determined by by calculating the different forms of energy and determining their difference. But which forms of energy are prevalent in archery?
When considering the steps in firing a bow, the forms of energy are quite obvious to see. Before the bow is drawn, Chemical Ptential Energy (ECH), is sored in the archer in preparation for the shot. Once the bow is drawn, and the bowstring pulled past equilibrium (when all forces acting on the string are balanced), Elastic Potential Energy (PE) is stored in the bow. When elastic materials (such as string, rubber band, springs) are compressed or stretched, they store elastic energy. Then, as the string is released, the energy is transferred into a different form: Kinetic Energy (EK). This describes the energy of an object in motion. As the arrow soars towards the target, there is also Gravitational Potential Energy (EP). This is the energy that results from gravity’s attraction to an object relative to its vertical height and mass. Finally, as the arrow strikes the target, Sound Energy (ES ) and Thermal Energy (ETH).Alternatively, Power (P=W/∆t) is defined as the “rate at which work is done” (Basic Terminology and Concepts: Power). The amount of power produced is dependent on the ratio of work to time. In archery, different bows are capable of producing different amounts of Force depending on their draw weight. Bows with a higher draw weight are able to project arrows with a greater force (and ∴ more energy) in a smaller amount of time. For these reasons, the Power rating on these bows will be much greater than that of lower draw weight bows because they can perform more work in less time.
-Archer in action
The Law of Conservation of Energy states that energy cannot be created or destroyed, but can be converted into different forms and transferred to different locations within a system. As a result, the total energy within a system will remain constant. Therefore, with regards to archery, the amount of energy remains consistent from the time the arrow is fired to the moment it strikes the target, effectively transferring the energy out of the “system”.
Its the law!