Force
Force is an elementary concept in biomechanics, therefore it will be explained in an individual chapter. Without applying force we would be completely helpless in sport and physical exercise. Forces make us move, stop, or change direction. Forces are even important also when we stand still. For example we exert forces to keep our upright posture. To keep balance while riding a bicycle or skiing also requires to be able to control various forces.
If we omit inertia forces, force is a quantitative description of the interaction between two physical bodies, such as an object and its environment. For the needs of biomechanics we can state, in a simplified way, that force is produced by pull, push, or gravity. Physical bodies in contact always exert forces at each other. Forces always occur in pairs. Every action is accompanied by a reaction of equal magnitude but opposite direction.
Force causes free body to undergo a change to its speed or a change to its shape.
To study many topics in human biomechanics it is sufficient to replace human body with a model composed of rigid segments. In biomechanics we use models with various numbers of segments, from one to multi-segment models, which describe tiny parts of human body. Objects that are in contact with human body are often regarded as rigid bodies and in that case we can make use of the knowledge of rigid body mechanics. In rigid body mechanics forces do not cause bodies to undergo a change to their shape, only a change to their speed, in the absence of opposing forces. The unit of force is newton (N), named after the famous physicist Sir Isaac Newton. The symbol used is F. The force of 1 N is equal to the amount of net force required to accelerate a mass of 1 kg at a rate of 1 m·s-2.
A force has both magnitude and direction.
Force is thus a vector quantity5. Vector is a quantity completely specified by its magnitude and its direction.
5 VVector physivcal quantities are marked in bold italics.Zpět