The Laws of Physics and Dance

Kathryn Morgan Haul

I’ve been wanting to write about Physics and Dance for a while but I never know where to start. Physics observe the world we live in and explains it with laws and principles and dance is surely Donsomething to observe!

Physics principles can be applied to any kind of movement, including dancing. And grasping these concepts will help any dancer understand and even improve their dance technique! It can also help some science enthusiasts to appreciate dance differently.

Don’t worry… I will not get very specifics on the maths of the physics in dance but I will do my best to describe some concepts that I think you will find useful.

Describing and explaining movement

Kinematics, according to the definition in Wikipedia, that describes the motion of points, bodies (objects), and systems of bodies (groups of objects) without considering the forces that caused the motion. In this case, the dancer is the “systems of bodies”.

As mentioned above, this can be helpful to describe some aspects of the movement, like position, velocity and acceleration.

These concepts can be used to estimate how long a jump will be or how high a dancer can get during this jump, even where and when a couple of bodies will find themselves when dancing as a duet.

When a body is suspended in the air, like when a dancer is jumping, gravity will be the only force that attracts the body of the dancer to the ground. Since we know the value of the acceleration due to gravity, we can easily describe the type of movement that a dancer makes during a jump, which resembles to the one of a projectile!

Watch this wonderful video on the Biomechanics of Grand Jeté, by Kelly Rosenbaum!

We all have to go through Newton’s laws of physics as we go through high school and apply them to everyday life examples. Up next, I am going to briefly explain the three laws of Newton and give a few examples on how they can apply to dancers.

First Law of Newton and the concept of Inertia

Newton’s First Law, also known as the principle of Inertia states that an object will remain at rest if it was resting or in uniform motion in a straight -if it was moving like that- unless there is an external force that changes their state.

In simple words, if your body is moving in a certain way, unless you make the decision to change it, it is going to keep moving in the same way. This is called Inertia. And the same think happens if you are not moving at all.

This is why it is so hard for us to come out of bed in the morning! Just physics!

Now… in which dance movements can we see the Principle of Inertia in dance?

Well… this one is easy to spot on turns (did you get it? because you have to spot while you turn otherwise you lose balance!)

During Châinés turns the dancer will make a series of rapid turns in a diagonal or in circles. If you are familiarized with these type of turns you will know that is easier to keep turning than to stop. You have to tell your body to stop in a certain position and end the turns, possibly, gracefully.

In other types of turns, like pirouettes, if the technique is done right, any dancer would continue to turn indefinitely until they decide to stop because of the principle of Inertia. But sometimes it is not always the case.

You may notice that it is easier to turn on demi point shoes or point shoes than barefoot, and it gets even easier when you are using a turnboard! (Read: What is a Turnboard and How to use it)

This is because there is a force called friction that the floor makes when it is in contact with our shoes. This is actually something good because otherwise we wouldn’t be able to walk without falling!

Which us to the Second Law of Newton…

Second Law of Newton

When there is a net force that is applied to a body in uniform movement or at rest, meaning the acceleration is 0, there is going to be a change in the acceleration of the body that it will change its speed and direction.

The Equation for this Law is F=m a, where F is the force, m is the mass, and a is the acceleration.

The stronger the net force (F), the greater the change in the movement. In the case of the friction we can use dance shoes (or even socks) that will decrease the friction between the floor and our feet so we can spin a little more!

Another variable that we observe in the equation is the Mass. This is the mass of the body that is affected. The heavier the body, the “harder” it will be to change its speed and/or direction. You can think of partenaire dance here, when a dancer jumps to another one it is a lot easier to catch a lighter dancer than a bigger one!

This doesn’t mean that you have to be super skinny in order to dance or that you can’t catch a dancer that is bigger than yours. This is why we train technique and strength!

 

Third Law of Newton: opposite forces

The third Law of Newton states that for every force that acts on an object (or in our case the body of a dancer) there is going to be a force of equal magnitude but opposite direction which acts back on the object which made the force.

When you prepare for a jump, you need to plie which means bend your knees and then push the floor. When you push the force you are applying a force to the floor and, as a response, the floor will make the same amount of floor but in the upwards direction so you will jump!

If you want to jump in the forward direction, like in a grand jeté, the force applied to the ground should be in a diagonal direction, opposite to the direction of the jump.

You can also think this law in terms of internal forces within a dancer’s body. In order to have proper posture for dance and stand in releve you are going to push the ground so it will push you. But you also have to push from your center up so you balance the forces within your body.

See how these two dancers apply the Third Law of Newton in order to mantain equilibrium between them.

Physics is everywhere!

I hope I gave you an overview on some of the principles of physics that are applied to dance. If you don’t know them yet, don’t worry. As dancers, we usually apply these

concepts (and many others) instinctively, without consciously thinking about them.

If you want me to talk about something in particular or have any doubts, please write them below and I will write about it!

Lately I haven’t had that much time to work on my site so it may take me some time but I will do my best!

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In the mean time, watch these great explanation on the physics of fouette turns, by Arleen Sugano.

 

 

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