PHYSICS III MOTION IN PLANE INTRODUCTION

CHAPTER 3

MOTION IN A STRAIGHT LINE
INTRODUCTION

• Motion is change in position of an object with time, body is said to be in motion if it continuously changes its position w.r.t any fixed point.
Point objects: When the size of the object is much smaller than the distance it moves in a reasonable duration of time, the size of objects can be neglected and they can be considered as point-like objects without much error.

Eg; 1) planetary motions. size of the planet is ignored compared with the size of the orbit. 2) Length of a bus may be neglected compared with the length of the road.

Motion in 1, 2 & 3 dimensions

Study of motion of objects along a straight line, is known as rectilinear motion. One dimensional: If the motion of a body is confined to one direction.

eg: an ant moving on a stretched wire, a train running on straight rails, a bus running on a straight road. Two dimensional: If a body is free to move in any direction in a plane surface.

eg: an ant moving on a table, movement of carom coin, movement of the tip of a pen while writing.

. Three dimensional: If a body is free to move in any direction in space. eg: an ant moving over an orange, A fish moving under water, motion of an airplane in space.

Relative concept: not an absolute concept.

Mean vel. of earth in its orbit about the sun, V =d/t =2nr÷t =2nx150x10 + 365x24x60x60=29.86 km/s //

When you say that a car is moving on a road, you are describing the car with respect to a frame of reference attached to you or to the ground. But with respect to a frame of reference attached with a person sitting in the car, the car is at rest.

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