Movement of a car, movement of a bike, a human walking, a bird flying, a dog running, a baby crawling, all of these things have a similarity. It is the fact that, all of them move in a straight line.
As per Newton’s first law of motion, a body tends to be in state of motion or in a state of rest until and unless acted upon by some external force acting against it. So a body moving in a straight line will continue to do so till a force modifies its direction or alters its path.
TYPES OF MOTION
In a three dimensional space that we live in, three coordinates are used to describe the position of an object – x coordinate in the direction of x-axis from origin, y coordinate in the direction of y-axis from origin and z coordinate in the direction of z-axis from origin. Let’s say a point is (3, 4, 5). It signifies 3 as the x-coordinate, 4 as the y-coordinate and 5 as the z-coordinate. Now, a motion can be described in terms of number of axis used by a body.
- ONE DIMENSIONAL MOTION – If only one of the three coordinates describing the position of the body changes with respect to time, then it is called one dimensional motion. For example, any object falling towards the earth because of gravity (only the y-coordinates change), a train moving along a straight track (the coordinate along the straight track changes, rest are fixed).
- TWO DIMENSIONAL MOTION – If two out of the three coordinates describing the position of the body change with respect to time, then it is called two dimensional motion. For example, rotation of earth around the sun (only two coordinates forming the circular path change), movement of boat (since the boat does not go up or down, movement is across 2 coordinate axes).
- THREE DIMENSIONAL MOTION – If all the three coordinates describing the position of the body change with respect to time, then it is called three dimensional motion. For example – airplane flying in the air (it changes all x, y, z coordinates), a kite or a bird flying in air, water molecules moving randomly when water is heated.
With the external force is applied, a body can change its motion across one dimension, two dimension and third dimension, as the external force might change the path of the body.