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# The Physics of Dance

Sarah Johnston explains the intersection of science and art in dance, and how they play off one another to create a beautifully impressive form

Image(s): behance.com

If you’re a dancer trying to improve your technique, the last place you’d go looking for advice is probably a physics textbook. However, dance – like everything – relies on science. Whether you want to jump higher, turn faster, tap louder, or stretch further, there is an underlying scientific principle you are harnessing to be able to move the way that you do. Dancers are often taught techniques which involve using this science without realizing, so I want to shed some light on why we dance the way that we do.

I want to begin with something quintessential to dance, but also to many other artistic sports: turning. If you’ve ever received dance training, you’ve probably heard the same advice about turns: hold your core, move your arms to first position as you turn, and ‘spot’ your head by trying to keep it on the same spot for as long as possible before snapping it round. Each of these things relies on an innate and basic principle of movement mechanics. When we turn, we harness something called angular momentum, which is a measurement of the momentum of a body which is rotating. Angular momentum is a product of the radius of the object (how wide it is) and its linear momentum (which is its mass multiplied by its speed). Momentum must be conserved, it is a physical law of the universe. This means if you change the radius of the object that is spinning, the speed of the object must change to keep the momentum constant.

Balancing is not only artistically impressive but is physically impressive because of the huge pressures your body is subjected to when you do it. Pressure is defined as the force per unit area, where the force is due to your mass, and so if the area you are balancing on is small e.g. just the ball of your foot, then the pressure your foot is exerting is incredibly large. Take for instance a dancer standing on pointe. The total area of the pointe shoe is very small, a few 10s of cm2, and if the weight of the dancer is 50+ kg then you can end up with pressures of thousands of Pascals. In fact, a dancer in a pointe shoe can exert more pressure on the ground than a tank, because although the tank is much heavier, its weight is spread over a much larger area. This is why it is so important to have properly fitted dance shoes, to make sure that all of the pressure you’re exerting on the ground doesn’t just break your toes.

I might even go as far as to say that gravity is the worst enemy of dancers. Dancers can make jumps and leaps look effortless, when they are in fact battling against a fundamental force. The gravitational field on Earth is 9.8 Newtons per kilogram, which means that for every kilogram you weigh there are 9.8 Newtons of force pulling you downwards. Gravity only affects vertical motion and works to pull the dance down, so jumps usually look like a parabola (arch) shape if you watch them from the side as the dancer continues to move horizontally while they jump. However, the effect of gravity limits how long they can spend in the air, as it causes them to accelerate back towards the ground. This means dancers need to come up with inventive and artistic ways to increase their ‘air time’ or at least appear to increase it. Sometimes when you watch a dancer, they can create an illusion of floating or hanging in the air. When a dancer reaches the peak of their jump (the highest point), they can tilt their head back and bring only their legs and arms up while keeping their torso steady which makes it appear as though they are still moving upwards. This gives the illusion of them being frozen in the air for a moment, making them seem to float. If you are trying to get a bit of extra height on your jumps, as well as your take-off, make sure you're harnessing your body whilst in the air.