# Motion

Motion is defined as the change in the position of an object over time and mathematically described in terms of displacement, distance, velocity, acceleration, speed, and time. When we talk about motion of points, we refer to points belonging to rigid bodies, intending to establish the connection between the motions of the two entities – point and body – as determined by the position and constraints. The motion of a body is observed by attaching a frame of reference to an observer and measuring the change in position of the body relative to that frame.

If the position of an object is not changing relatively to a given frame of reference, the object is said to be at rest, motionless, immobile, stationary, or to have a constant or time-invariant position with reference to its surroundings. As there is no absolute frame of reference, absolute motion cannot be determined. Thus, everything in the universe can be considered to be in motion.

## Types of motion of a body

There are various types of motion: rectilinear, curvilinear, circular, parabolic and elliptical: all these are called trajectories. By composing the individual motions together, it is possible to determine the trajectory of a body in space. Among the motions of classical physics, we remember:

• Translation
• Rotation
• Roto-translation
• Plane motion
• Uniform motion
• Uniform straight motion
• Smoothly accelerated motion
• Relative motion
• Cyclical motion
• Circular motion
• Transient motion
• Anharmonic motion

## Transmission of motion

The motion transmission systems allow a transfer of mechanical energy from one object to another without changing the nature of the movement (rotational to rotational or translation to translation). For example: in gears, or friction wheels, the motor wheel transmits its rotational movement to the following wheel. Both wheels are in rotation. The transmission of movement can occur by direct contact between two mechanical pieces or with the help of an intermediate device such as a chain or a belt.

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