Work, Power, & Energy
Today we're talking about biomechanics and three basic principles that often get misunderstood: work, power, and energy.
What is work?
If you look up the definition, you’ll probably arrive at something like this: activity involving mental/physical effort to achieve results. Makes sense, right? It takes mental effort to drive, process documents, or remember where you put the keys.In mechanics work is force multiplied by displacement. Displacement is simply the shortest distance from your FINAL destination back to where you started. It’s different from distance because if you end where you start your displacement is zero while your distance would still be some number.
Work = force x displacement. Mechanically, you must apply force and their needs to be some sort of displacement for work to occur. Holding a hotdog isn’t work. Holding a board for your friend while he hammers it (hopefully he has good aim) is not work. Throwing a hot dog up in the air or raising a board from the ground is work because force is applied, and displacement occurs.
It’s also worth noting the formula above is for linear work when the force applied is in the same direction of displacement traveled. The true formula is W = F×d×(cos(θ)) where cos is the angle between the force and displacement.
Work example.
Work is measured in Joule’s, force in newtons, and displacement in meters. Work (j) = force (n) x displacement (m). Let’s look at an actual example.Bobby likes to push crates. Because that’s what he does for fun. He pushes a crate directly parallel to the ground at a force of 12 N for 5 m. How much work did he do?
Work (j) = force (n) x displacement (m) = Work (j) = 12 n x 5 m = 60 j
What is power?
We hear this term thrown out all the time. That man is power-hungry. That woman has a powerful kick. But what does it mean mechanically? As we learned from our first term you come across many different definitions for the same words. Having a clear understanding of what a word means helps clear up confusion. Mechanical power is simply how much work you do over a certain amount of time.Power = work / Δ time (change in time, time elapsed)
Power example.
Power is measured in watts, work in joules, and time in seconds. Power (w) = work (j) / time (seconds). Taking the same example above, let’s add on to it. Let’s say Bobby goes Hulk on that crate and pushes with a force of 12 N moving it 5 m in 3 seconds. Here is what that looks like.Power (w) = work (j) / time (seconds = Power (w) = 60 j (from first problem) / 3 s = 20 w
This equation tells us you can increase your power by doing more work in less elapsed time or producing more force lifting the same weight in the same amount of time.
What is energy?
Energy is a beautiful concept in physics. Energy cannot be created or destroyed, but It can be transferred from one object to another. In physics, there are many types of energy and many equations for each type. Two common types of kinetic energy and potential energy.Kinetic energy is a result of movement. You develop kinetic energy running down a soccer field or running down the street to catch the bus. The amount of energy it would take to stop you from moving is kinetic energy.
Potential energy is a result of an object's position. If you throw a ball in the air as the ball travels upward it has kinetic energy, and this is transferred to potential energy as it starts to fall.
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