Motion
You see a parked car in front your house. Five minutes later you look out again but the car is in a different spot. The car has moved. You don't know how it moved. It could have moved in a straight line to its new destination. It could have done three circles and a figure eight for all you know. But none of these possibilities changes the truth of the fact that the car has moved.
Usually, when we see something move, we don't just see it in two seperate places. We observe the moving object continuously. Although, if you think about it, that could be considered watching it as a series of observations with very little time between each one.
There some very important things you should know about the nature of motion. The change of position of a moving object, for instance. That change of position in a particular direction is called displacement. A displacement has magnitude, direction, and a point of origin.
Relative motion is another concept of which you should be aware.Relative motion can be detected by comparing the displacement of one object with respect to another. The reference object is usually stationary. In the example with the car, the stationary objects are the house and street. Therefore, motion could be defined as the displacement of a object in relation to objects that are stationary.
Speed is the time rate of motion. This means if you walk 3 meters per second, in 1 second you've walked 3 meters. In 2 seconds you've walked 6 meters, and in 3 seconds, 9 meters. Your average speed is found by dividing the total length you've walked by your total time.
When both speed and direction are specified for the motion, the term velocity is used. In other words, velocity is speed in a certain direction. A person walking east doesn't have the same velocity as a person walking north, even though their speeds are the same. Two people also have different velocities if they walk in the same direction, but at different speeds. If an object travels at a constant speed in one direction, the motion of the object is said to be variable.
The gas pedal of a car is sometimes called the accelerator. When you drive a car along a street and press down on the accelerator, the car's speed increases. This is called acceleration. When you put on the brakes, the car slows down and finally stops. This is called decelerating.
Acceleration is defined as the rate of change of velocity. It can be positive or negative. A car that goes from 0 m.p.h. to 60 m.p.h. in 10 seconds has a greater acceleration than a car that goes from 0 to 60 in 15 seconds. The first car has an average acceleration of (60 m.p.h. divided by 10s)=6 (m.p.h.)/s. The second car has an average acceleration of 4 (m.p.h.)/s.
