Motion takes place in accord with 3 scientific laws discovered by Sir Isaac Newton.
Understanding these laws of motion is invaluable for anyone involved in dance, yoga, fitness, our orthopedics course because it adds more precise imagery of force, gravity, and reaction to the mental repertoire. These laws will provide a deeper understanding of how the body works and how it deals with inner and outer forces. Successful movement involves dealing efficiently with these forces.
Newton's Law Of Motion
Isaac Newton was born in England in 1643 and formulated the 3 basic laws of motion in his journal while he was still attending college in Cambridge. These laws are the law of Inertia, the law of Acceleration, and the law of Reaction.
1st Law of Motion : Inertia
The tendency of an object to resist changing state, to remain at rest or to keep moving, is called inertia.
You experience the effects of inertia when the car you are riding in suddenly accelerates and you are pushed back into your seat. If the car comes to a sudden stop, you are pitched forward because you stay in motion. To move any part of your body, you must overcome inertia. If you are leaping across a dance floor, you must exert force to stop your forward motion. Inertia depends on a body's mass, the larger the mass, the greater the inertia.
Inertia is subjectively experienced as greater under certain conditions. A baby seems heavier when he is sleeping than when he is awake. People who think of themselves as heavy are harder to carry. Efficient movement is smooth and continuous. This is a sign that you are using your inertia, your tendency to keep moving optimally.
2nd Law of Motion : Acceleration
Newton formulated that acceleration is produced when a force acts on a mass. In other words, an object moves because a force is at work to make it move. In this law, the greater the mass, the greater the amount of force needed, or heavier objects, the ones with more mass, will need more force, should they be moved. The speed of an object with the same mass will depend on the amount of force applied to it. You know this law intuitively. To kick your leg higher and faster, and to jump higher as well, you need to produce more force in your muscles.
Speed is the magnitude of velocity without any specific direction. Velocity is the rate of change of position of an object. Any change in the speed of an object is called acceleration. Acceleration can also induce a change in direction. When the car is accelerating, you feel the seat pushing against your back because a force is being applied to your back. The amount of acceleration you experience depends on the strength of this force and your own mass. The greater the force and the smaller your mass, the more you will accelerate.
It is easier to partner a smaller, lighter dancer because the force you apply has a greater effect. Before executing a lift, you usually practise the step on your own. Obviously, when lifting your partner, increased effort is required. Because the mass of the moving system has increased, you need to exert more force. Acceleration becomes more difficult. Force, mass, and acceleration are always related. If your repeat the same step without your partner, it seems easy because your muscles are attuned to moving a much larger mass.
It is interesting to note that at the cellular level, gravity, and therefore Newton's laws, play much less of a role. Molecules in the cells are moving through the cellular fluids at a very rapid pace relative to their size and appear to be moving in a random fashion called Brownian motion.
3rd Law of Motion : Reaction
Newton's 3rd law states that for every action there is an equal and opposite reaction. Action is another word for force. A reaction is a force that acts in a direction opposite to the action. If forces act on an object without causing it to move, then all the opposing forces add up to zero resulting force.
Force always come in pairs. As soon as two force contact each other, reaction force is involved. If you lean two books against each other, each one exerts force against the other. When book 1 applies a force to book 2, book 2 immediately applies a force equal in magnitude and opposite in direction to book 1.
Objects can sit on top of, be braced against, or hang from one another. If you place one hand on the ballet barre, you and the barre exert force against each other. The ropes holding a docked ship exert force on the ship; the ship tugs on the ropes. A chandelier and the ceiling it hangs from exert force on one another.
If you are standing still, the ground reaction force equals your weigh. Every step you take elicits a reaction from the ground called the ground reaction force (GRF). If the GRF is insufficient, as on quicksand or on a thin layer of ice, you will sink. If you push rapidly against the ground with a force that is greater than your weight, the ground pushes back with a force greater than your weight, propelling you upward. The moment you leave the ground and cease to exert force against it, the ever-present force of gravity returns you to Earth rather quickly. This is what happens when jumping on a trampoline. For the moment, the surface of the trampoline pushes against your feet with a force greater than your weight. When you come back down, the situation reverses. Now your feet are pushing against the trampoline with a force greater than the reaction of the surface of the trampoline. A rocket is able to escape gravity by continuing to exert force against it after blastoff.
Reaction force in the form of pulls and pushes are what create balance in partnering and are the spice of contact improvisation. Used inventively, reaction forces make apparently gravity-defying movements possible. Reaction force may be imagined at any level in the body ~
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