# The types of speed and the factors necessary for the description of motion

## The motion

The motion is the change of the object’s position ( location ) as the time passes according to the location of another object , The motion happens all around us , We see the objects such as the cars , the people and the balls move in different directions with different speeds  everyday .

When the object’s position changes as the time passes according to the position of another object , We can say that the object is in a state of motion , the path of a moving object may be straight , curved or combination of both .

The motion of the train or metro is in one direction ( forward or backward ) and in a straight line ( not in a curved line ) , The train motion is considered from the motion in one direction as the train moves forward or backward but it does not move upward or downward ?

### The speed

We can describe the motion of some objects around us as fast and some others as slow , The speed is a physical quantity which is used to describe and measure the motion of objects , ( Speed = distance/ time ) .

The two factors necessary for description of motion ( the speed ) are the distance covered by the moving body and the time taken by the moving body to cover this distance .

The speed is the distance moved through a unit time , the object’s speed increases as the time decreases to cover the same distance , The speed of object is inversely proportional with the time .

The object’s speed increases by increasing the covered distance at constant time , The speed of object is directly proportional with the covered distance .

When the distance is measured by meter and the time is measured by second , So , The measuring unit of speed is ( m/s ) , when the distance is measured by kilometer and the time is measured by hour , So , the measuring unit of speed is ( km/h ) .

### Kinds of speed

There are the regular ( uniform ) speed and the irregular ( non-uniform ) speed , The regular ( uniform ) speed is the change of object’s position by equal distances at equal periods of time ( whether the distance and the time are short ) .

The irregular ( non-uniform ) speed is the change of object’s position by unequal distances at equal periods of time , or it is the change of the object’s position by equal distances at unequal periods of time .

It is difficult to determine the amount of irregular speed of the object , So , we use the average speed which is the total distance covered by the moving object divided by the total time taken to cover this distance .

The average speed represents the regular speed by which the moving object moves to cover the same distance at the same period of time .

When the average speed of a moving body equals the regular speed , the motion is described as the regular motion , when the average speed of a moving object does not equal the regular speed , The motion described as the irregular motion .

The relative speed is the speed of a moving object relative to an observer , Measuring the relative speed depends on the position of the observer who determines the magnitude of this speed .

If the observer is at rest , So ,  ( the relative speed = the real speed of the object ) , If the observer is moving in the same direction of the moving object , So , ( The relative speed = The object’s speed – the observer’s speed ) , if the two speeds are equal , So , The relative speed equals zero .

If the observer is moving in the opposite direction of the moving object , So , ( The relative speed = the object’s speed + the observer’s speed )  .