Irish Dance Defying Gravity

    This past weekend, I was watching my friends compete at the Irish Dance Regional Championship. I was a competitive Irish dancer my whole life, but I never realized the level of physics that is involved in this sport until our discussion of forces in our class! In Irish dance, one specific move requires you to push off the ground to do a leap in the air. This move is done in shoes similar to ballet shoes. A visual of the lead dancer of Riverdance performing this move is shown below.

    You can see that due to the force of gravity on the dancer, they go up and come down relatively quickly. Newton's third law stating that "every force has an equal and opposite force" can also be seen between the dancer's foot on the ground and the ground pushing back on the dancer's foot to help propel her upwards into the air. It was obvious to me and my fellow dancers how much of a toll this sport takes on your bones and muscles, but we didn't quite focus on why certain injuries were so common. I had overuse tendon and muscle injuries multiple times a year, which I can now attribute to the level of force acting on my body when I would push off the ground to leap, like my friend here above :) 

    I wanted to take a look at what the actual value of a typical Irish dancer's force would be to push up off the ground. I used a mass of 40 kg with an average acceleration of 1.5 m/s^2. The calculations to find the force of a dancer's push off the ground are found below.

F	X	Y
Fp	-	Fp
Fg	-	-mg

F = ma = Fp - Fg

(40 kg)(1.5 m/s^2) = Fp - [(40 kg)(9.8 m/s^2)]

Fp = 452 N

    Now it makes sense why injuries are very common in this sport. That's a lot of force on a small person!

   

 I always felt like Irish dancers were able to defy gravity, but PHYS 111 actually allows me to prove it mathematically now!