Translations of Encyclopedia about Physics

Simple Motions

Motion is a basic activity of a human. Our muscles, heart and lungs continue to move even while we sleep. From a physical point of view, motion is each change in an object’s location.

Motion, or movement, must be understood as a relative concept in that no absolute reference system exists. For example, an object in a car is considered as in a still state when compared to the car. A road is considered in a still state relating to the earth, but the earth revolves around the sun while the sun circulates within the milky way.

The relative concept of motion means that the still position of an object or its motion is always in relation to some other object, as such creating a reference system. An object observed from different points of view may show different forms of motion. For example, if a car is parked in a garage, the car is perceived, together with the garage, to be in a still state, even while both the car and garage are revolving with the earth around the sun.

Motions have direction and dimension and their measurement is speed. When observing motion, physicists place emphasis on uniformity and the trajectory shape (path) of the motion. A trajectory is composed of several points which the object passes through.

A uniform or steady motion is when an object travels at a constant and unchanging speed while its direction changes. The best example of this type of motion is a circular motion. While an object travelling uniformly around a central point continually changes the direction it is travelling in, its speed remains constant.

Motion is linear if its direction does not change, although its speed can be changing. An object whose speed changes can be accelerating or decelerating, such as when a car brakes.

The change in an object’s speed is referred to as acceleration, regardless of whether the speed is increasing or decreasing (if decreasing than it is referred to as negative acceleration). The acceleration of an object is directly proportional to the force acting on the object and indirectly proportional to the mass of the object. While thinking of this, we did not consider the other forces which change proportionally with the increasing speed of the object, such as wind resistance or the friction of the object or its parts.

The motion of a car along a road can be described using simple movements. The gas and brakes within the car can change its motion and the car’s steering wheel is used to change the car’s direction.

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