Basic laws of classical mechanics | Biomechanics in sport

Basic laws of classical mechanics

Law of Inertia A body remains in its state of uniform motion as long as no force is acting on it. Example: A vehicle is at rest on the road. In order to change this state, a force must act on the vehicle.

If the vehicle is in motion, external active forces act on it (wind resistance and friction). Forces that can accelerate a vehicle are engine and slope downforce. Law of Acceleration The change in motion is proportional to the force acting on the vehicle and occurs in the direction in which that force acts.

This law states that a force is needed to accelerate a body. Law of counteraction An acting force always produces an opposite force of the same magnitude. In literature one often finds the term actio = reactio. This third law of classical mechanics means that the force applied around one’s own body or an object in motion produces a counterforce.

Biomechanical principles

In general, biomechanical principles are understood to mean the exploitation of mechanical laws for the optimisation of sporting performance. It should be noted that biomechanical principles are not used to develop techniques, but only to improve techniques (see Fosbury Flop in athletics). The biomechanical principles are:

  • Principle of maximum initial force
  • Principle of the optimum acceleration path
  • Principle of coordination of partial impulses
  • Principle of reciprocity
  • Principle of the rotational recoil
  • Principle of conservation of momentum

Definitions

Body centre of gravity (CSP): The body centre of gravity is the fictitious point that lies in, on or outside the body. All forces acting on the body have the same effect in CSF. It is the point of action of gravity.

In rigid bodies the CPG is always in the same place. However, this is not the case in human bodies due to deformation. Inertia: Is the property of a body to resist an attacking force.

(A heavy car rolls downhill faster than a light one for the same volume). Force F=m*a: Force means mass x acceleration. A force acting on a body causes a change of location.

Therefore heavier cars need stronger engines to accelerate at the same speed. Impulse p=m*v: The impulse is the result of mass and speed. This becomes clear when serving in tennis.

If the mass (weight of the racket) is high, the impact speed does not have to be as high as with a light racket to achieve the same effect. Torque M=F*r: The torque is the effect on a body that leads to an acceleration of the body around an axis of rotation. Mass moment of inertia I=m*r2: Describes the inertia when changing rotational movements.

Rotational moment of inertia L=I*w: Is the rotational condition of a body. The angular momentum is generated by an eccentrically acting force and results from the mass moment of inertia and the angular velocity. Work W=F*s: To accelerate a body, work is complex.

Defined as a force acting over a certain distance. Kinetic energy: Is the energy contained in a moving body. Positional energy: Is the energy contained in a lifted body.