Physics Involved- Action-Reaction Force Pairs, Newton's First and Second Law, Friction, Energy and Work
Hey readers, I recently discovered a workout called Burpees! Not only are Burpees a fantastic cardio workout, but also there is a ton of physics involved! To truly understand what is happening as you work those muscles, lets jump right into all the science:
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Hey readers, I recently discovered a workout called Burpees! Not only are Burpees a fantastic cardio workout, but also there is a ton of physics involved! To truly understand what is happening as you work those muscles, lets jump right into all the science:
- First of all, it’s important to note that doing this on a floor with a high coefficient of friction such as a carpet or on concrete is important because when landing and doing pushups, you want to slide as little as possible so you can keep a firm position. Fortunately Newton’s First Law of Motion doesn’t apply here because we have friction to keep us from moving forever.
- To begin, get into a crouch position. As you lower yourself to this crouch position, you need to push on the ground with less force then you originally were so the gravitational force downward overtakes that normal force upward and you begin to accelerate downward. You must stop yourself by stabilizing the normal and gravitational forces and push hard on the ground. Believe it or not, the normal force of you on the ground downward is equal to the normal force of the ground on you upward, and this always stays true even when changing forces so you can go up and down.
- Next you push your legs out behind you by exerting more force onto the ground so the ground on you is more force than gravity on you so you go up in the air and are able to readjust to a push up position.
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- On Sam’s page, he talks about the physics in a pushup, so go ahead and do one! I know you are working hard to keep yourself up after that pushup, but in physics terms you are actually doing no work! The formula W=Fd considers displacement, and you are not moving while holding yourself up, making d=0 and you are doing no work. Your arms are getting a good workout here as they must apply a lot of force depending on your mass, assuming you are going the same speed, as shown in Newton’s Second Law, where F=ma.
- Afterward you bring your legs back under you to return to a crouching position, and the concept is the same as when you pushed your legs out.
- Finally, you jump! There is displacement as you fly up into the air and because you push off the ground to produce it, there is work-in. As you go higher and higher into the air, you gain gravitational potential energy but since you go ground-to-ground the potential energy doesn't really do anything. Unfortunately there is no kinetic energy as that is concerned with just the start and end points of the jump, which you are at rest on the ground for. While in the air, you are considered to be in free-fall because the only force to act on you is gravity which brings your speed down 9.8m/s until you hit the ground. Finally when you land, there is work-out as the ground forces your legs to bend from the crashing force with the ground.
- Now rinse and repeat!
Here's a YouTube video for all you visual learners out there: