Motion
Motion is apparent in widely ranging phenomena, from blood cells squeezing through capillaries to planets moving across the sky. Motion is the displacement of an object with respect to objects that are at rest. Historically, motion was one of the first phenomena to be studied carefully. Some progress was made in the understanding of motion in ancient times, particularly by the philosophers of classical Greece, but it was not until the Renaissance that the basic laws of motion were discovered. Many individuals made important contributions, but two stand above the rest : Galileo Galilei ( 1564 – 1642 ) and Isaac Newton ( 1642 – 1727 ). If Galileo’s predecessors had placed a greater value on experimentation, they might have made more progress than they did. Instead most natural philosophy was based on logical argument and the constraining influence of a particular school of thought. The transition that Galileo and others made from dogma to experimentation was not without pain; Galileo himself was forced by the Inquisition to recant his work and lived the last years of his life under a form of house arrest.
The central ideas regarding motion developed by Galileo and Newton remained essentially intact until 1905, when Albert Einstein ( 1879 – 1955 ) published his paper on the theory of relativity. Even today, the classical theory of Galileo, Newton and others describes motion with extremely good precision as long as the object being described moves slower than about 1% of the speed of light. The study of motion is kinematics, motion being the displacement of objects with respect to objects that are at rest. Kinematics comes from the Greek word kinema, meaning motion, the same root from which we get the word cinema. Kinematics describes the position and motion of objects in space as a function of time but does not consider the causes of motion.( It deals with motion without considering the forces causing the motion ). The study of the causes of motion is dynamics which relates motion to the forces causing it and to the properties of the moving system.
Kinematics provides the means for describing the motions of varied things as planets, golf balls, and subatomic particles. Because of its precision and generality, mathematics is the natural language for kinematics. To adequately describe motion, one must be able to say where something is located within a given reference frame. Reference frame is a physical entity, such as ground, a room or a moving car, to which we refer the position and motion of the objects.
To say that space is three dimensional, it means that three numbers are needed to completely locate the position the position of an object. A system for assigning these 3 numbers, or coordinates, to the location of a point in a reference frame is called coordinate system. Because the coordinate system is a mathematical construction, you are free to choose the system that you want, orient it as you wish, and place its origin wherever you prefer.
TIME, DISPLACEMENT, VELOCITY AND ACCELERATION
Time is measured in terms of change. If nothing changes, then it is impossible to tell that time has passed. All devices that measure time measure change; i.e., days are measured are measured by the change in position of the sun in the sky, clocks measure elapsed time by the change in position of their hands.
Displacement is the location of an object relative to a reference point. Displacement is specified by the distance from a reference point (magnitude) and the direction to get to the present location. This implies that displacement is a vector quantity which has magnitude and direction. Distance has no given direction and has only magnitude. It is a scalar quantity.
Velocity and Speed. Speed is time rate of change of position while velocity is time rate of change of displacement. Velocity can also be describe as speed in a specific direction.
ν = Change in displacement = Δ S , ν is average velocity
Change in time Δ t
Acceleration is the time rate of change of velocity or the speeding up or the slowing down of bodies in motion. Acceleration is a vector quantity and has both magnitude and direction.
a) Positive acceleration ( acceleration,) – the speeding up of bodies in motion ( νf > ν0 ).
b) Negative acceleration ( deceleration) – the slowing down of bodies in motion ( νf < ν0 ).
Average acceleration, a = Change in velocity = Δ ν
Change in time Δ t