Kinematics
Motion
Motion can be defined as the process of changing position or place of a body in space.
Motion is the process of changing position.
Motion of a body can be described only if we know its position with respect to time. In order to study motion more easily, we classify motion as linear, rotary, and general.
Linear Motion17
In linear motion all particles of human body travel the same distance during the same time.
Linear motion can be further divided to rectilinear motion and curvilinear motion. In rectilinear motion all particles of the body travel the same distance along parallel straight lines. In curvilinear motion the trajectories of individual particles of the body are curved, although the orientation of the body in space does not change. As an example of rectilinear motion we can imagine a downhill skier going down along the fall line of a flat inclined plane. A good example of curvilinear motion is a gymnast on a trampoline who keeps his/her body in the same position but lands on a spot different from take-off18.
Rotary Motion19
In rotary motion all particles of human body travel along a circle or its part, unless they are in the axis of rotation.
Rotary motion (angular motion) of a body can take place about an axis that passes through the body or about an axis that does not pass through the body. A gymnast swinging on the rings is an example of rotary motion about an axis that does not pass through the body. Figure skater rotating on ice rink is an example of rotary motion about an axis that passes through the body.
Individual parts of human extremities also carry out rotary motion with their joints as axes.
General Motion
General motion is a combination of linear and rotary motions.
General motion is the most common type of motion in sport and physical exercise. Running and walking are among typical examples. In this case the trunk moves in linear motion as a result of rotary motions of individual segments of extremities. Riding a bicycle is another example of general motion.
If we resolve general motion into linear and rotary motions, it is easier to analyze.
17 Linear motion is also known as translatory motion.Zpět
18 Assuming the gymnast is not rotating in space.Zpět
19 Rotary motion is also known as rotational motion.Zpět