Thursday 5th December 2013
A journalist looked out over a crowded dance floor in Harlem and asked a nearby dancer, “What do you call this dance?” The dance did not yet have a name, but it was 1928 and Charles Lindbergh (nickname “Lucky Lindy”) had just “hopped” across the Atlantic, and so the “Lindy Hop” was born.
This may be an apocryphal tale but it has some truth in it, because this form of swing dancing certainly emerged from the ballrooms of Harlem at this time. The Lindy Hop was a coming together of tap, the Charleston and the Breakaway, and was danced to the swinging jazz rhythms of the time. The recent resurgence of swing music has put this dance firmly back on the dance floor. In fact, dance floors all over the country seem to be filling new Lindy Hoppers who are unknowingly becoming expert physicists.
For thousands of years, dancing was primarily a group activity with men and women dancing separately. When people danced with partners it was mostly in open hold, with just their hands in contact. There were exceptions, such as an Elizabethan court dance called the Volta, and a much earlier alpine turning dance called the ländler. Both involved the man lifting the woman from the ground, which obviously required a close connection – in the case of the Volta, this involved a male thigh under the female buttocks. Then, in 1814, the Waltz exploded onto the dance floors of Vienna. The ballrooms of Europe and America would never be the same. The Waltz was a “close hold” dance, with the man and woman’s bodies in almost constant contact.
These close hold partner dances were highly controversial. They were often viewed as a “gateway sin” – something that could lead on to more serious sins, such as gambling and fornication. Despite the negative press, however, partner dancing continued to grow and many new partner dances swept America and Europe. There were the ragtime animal dances of the 1910s, including the Bunny Hug, the Turkey Trot, and the Grizzly Bear. Then, in the 1920s, the energetic and leggy Charleston emerged with competitions, marathons, and a new democracy in dancing. No longer was position on the dance floor dictated by social status, but by merit. Women could choose whom they danced with and how they danced. Close or separate. Having learned a few simple moves anyone could dance, and dance they did. From this ferment the Lindy Hop emerged.
Lindy Hoppers developed a range of moves as varied as swing music itself. However, like any dance, these complex movements could only occur if an external force was acting on the dancer. For example, the turn of the Waltz is only possible due to friction between foot and floor and contact between “lead” and “follow” (traditionally, the man and the woman). The characteristic lift of the Volta is only possible as the lead dancer applies a vertical force to overcome the weight of the follow.
This requirement of force led, in part, to the traditional roles in the dance: male’s lead and female’s follow. The reality is more complex. The average man’s greater strength and height are said to give an advantage when leading the more physical aspects of the dance. However, the lead must also be sensitive to the interpretation of the dance by the follow, responding to the subtleties of their timing and style. The average female’s greater flexibility is said to allow for a greater range of body positions as a follow. Follows must also provide much of the physicality in the dance and must have the courage to throw themselves into potentially dangerous positions. For these reasons, I believe, dancing is the science of lead and follow not male and female.
For instance, when Fred Astaire and Ginger Rogers danced cheek-to-cheek in a close turn their two bodies achieved a beautiful line impossible for any individual. Dancing like this is a conversation in physics, where the bodies of both dancers are required to master the forces involved.
In close hold, bodies are joined at the hip and hand. The follow exerts an equal and opposite force through arms and body in response to the lead. These equal and opposite forces, in accordance with Newton’s Third Law of Motion, allow the follow to dance in synchrony with the lead: as a mirror image. This symmetry can only be broken if the pairs of forces become unbalanced, causing one or both of the dancers to accelerate away from the other. For example, the lead may provide a subtle signal indicating to the follow to reduce the resistance, accept the transfer of momentum, and move away into a backwards step.
This, and all forces, cause a transfer of momentum (which is the product of mass and velocity). So, when the lead applies a net force, momentum is transferred to the follow. The more of the lead’s mass (body) moves as the force is applied, the greater the transfer of momentum and so the more the follow’s mass will move. Also, the longer it takes to transfer that momentum the smoother the ride. This is the difference between the slow gentle acceleration and deceleration of a careful driver, and the painful jarring of rapid acceleration or an emergency stop. The constant contact and gentle tension between the bodies of dancers means that momentum can be transferred at any time and over any time period.
This is beauty of partner dancing. When dancing alone you are constrained by your abilities and by the physical reality of friction and gravity. These forces are reliable, adaptable and predictable, but unchanging. When dancing with a partner these forces are countered by two different minds and bodies, each with its own interpretations, motivation, timing, strength and style.
Lindy Hop dancers spend a lot of time in open hold with contact only through the hands. This allows both lead and follow to play with the forces, to add variations, to create a feeling of elasticity – of freedom. The follow may sit back on to the lead’s arm and kick out into a jazz step using the tension and elasticity to give the movement energy. This tension is not created by brute strength but core body muscles, body weight and the elasticity of joints and muscles.
The lead may equally bring the follow into a rapid but smooth version of the Twist. To do this the lead twists their body, transferring momentum to the follow’s body; the elasticity of joints and muscles cushions the momentum transfer, giving a beautifully smooth ride. Brute force of tense triceps and biceps would lead to insufficient momentum being transferred too quickly and the motion being jerky and unpleasant. This open hold also allows the follow and lead to improvise, to create art from their bodies or just make each other laugh.
Dancers often seem to get addicted to dancing, even feeling a visceral need to dance. There are many possible reasons for this. It could be due to neurotransmitters such as endorphins, serotonin and dopamine that are released as a result of the physical exertion of dancing. These chemicals do tend to improve people’s moods, but then they are released during most forms of exercise. Another possibility is that dancing with a partner increases the levels of oxytocin in the blood. The science of oxytocin is still unclear but most studies seem to suggest that within a safe environment oxytocin increases trust and our sense of belonging to a group. Maybe this is what keeps us coming back for more.
This increased level of trust may also allow moves on the dance floor that would otherwise feel unsafe: moves such as air steps. These are the most spectacular part of the Lindy Hop. Bodies, usually the follows’, fly through the air with seemingly little fear of falling. This can only occur when the applied force upwards exceeds the downward pull of gravity. This gives an initial upwards acceleration. But as soon as the lead leaves the ground this would become a deceleration and she would slow, stop, and start to fall – unless her partner boosts her upwards momentum allowing her to reach new heights impossible to gain alone.
A skilled dancer can manipulate their partner’s momentum with the application of only a small force and so change their momentum in any way they wish. Thus, with minimal effort a small jump can become a “honeymooner” with the follow finding themselves in the lead’s arms like a newlywed; being spun around and then gently placed back on the floor.
A more sedate form of momentum transfer is Lindy Hop’s version of a pirouette. It seems a simple move: the lead provides a torque, a rotational force, and the follow accepts the rotational momentum and spins. Luckily for the follow they have much more control over the move than that. If a follow sticks a leg out they can slow themselves down; by moving a mass away from the central pivot of the spin they increase their rotational mass (or inertia) and so slow down. The opposite is also true and so an ice skater can spin more quickly by moving their arms in. Alternatively, if a follow starts a spin with a leg out the lead must apply more force to start the turn but, when that leg is brought in that extra momentum is released and so velocity increases.
These spinning dancers seem to enter a world of their own where balance, speed and style are the only things that exist. But no world is so simple. We must add time and space to this world and the symmetry of these dimensions. It is not only the couple in close hold who are dancing in symmetry. Many moves have an element of symmetry and many others can be created using symmetry. Moves can be performed forwards as well as backwards in space, both clockwise and anti-clockwise. They can be translated by a degree or distance; each translation generating another set of possible moves depending on footwork and balance.
Moves can also be reversed in time. If you watch a video of a dance backwards a whole new set of moves appear, moves you can recreate on the dance floor. However, there are exceptions to this time symmetry, where the second law of thermodynamics becomes involved. For example, in a foot slide the foot is placed on the floor away from the body and drawn in. This creates friction and so generates heat. If you reverse this process, sliding your foot outwards, it does not cool the floor and so this move is not truly time reversible.
This world of time and space is a dancer’s to manipulate, up to a point. Yes, to dance is to create – to create your own world within rhythm – but even here the laws of physics must still apply.
When Frankie Manning helped bring the Lindy Hop back to popular attention in the 1980s he was a postal worker and an incredible dancer. He was also as much of a scientist as any laboratory worker. He took advantage of the science of time, space and biology and we can all do this, wherever we are. On the dance floor as in the laboratory, laughter, frustration, and tears run together for all of us who can hear the music.
f you want to read more about the physics of dance I can recommend Kenneth Laws (http://physics.dickinson.edu/~pod_web/) who has written some interesting books on the subject.
If you fancy having a go, most cities in the UK seem to have a Lindy Hop scene. It is great fun and Lindy Hoppers are generally really friendly people. Search on Facebook or on the web and something usually comes up.
If you want to watch more videos, try these:
Thank you to Alistair and many other Lindy Hop friends for their scientific input and the dances!