Motion

MOTION Motion If the position of an object changes as the time passes with respect to a reference point, then it is said to be in motion. Scalar Quantities The physical quantities which only have magnitude and no direction are called scalar quantities. Ex – Mass, distance, speed, time, work, energy, power etc Vector Quantities The physical quantities which have both magnitude and direction (and which can be operated mathematically only by vector algebra) are called vector quantities. Ex - Displacement, velocity, acceleration, momentum, force etc Distance Displacement Length of the path covered by a body It is the straight line distance between the initial and the final position of a body. It is a scalar quantity. It is a vector quantity. For a moving body it is always positive. For a moving object it can be positive, negative or zero. It is never decreased during a motion. It can increase or decrease during a motion. It is always more than or equal to the displacement covered. It is always less than or equal to the distance covered. Speed Speed of a body indicates how fast it is moving and is given by the distance covered by the body per unit time. Its SI unit is m/s. It is a scalar quantity. Average speed It is defined as the total distance covered by a body in a given time interval. (a) If a body covers a distance S1 in times T1, S2 in the time T2 and so on, then (b) If a body covers a distance S1 with a speed V1, distance S2 with a speed V2 and so on, then (c) If a body covers first distance with a speed V1 in time T1, the next with a speed V2 in time T2 and so on, then (d) If a body covers a distance with a speed u and an equal distance with a speed v, then Uniform Speed If a body covers equal distance in equal time intervals however small the time interval be, the body is said to move the uniform Speed. Velocity The velocity of a body indicates how fast it is moving in a given direction and it is given by the displacement covered by the body per unit time. Its SI unit is m/s. It is a vector quantity. Average Velocity It is defined as the total displacement of the body in a given time interval divided by the time interval. If the velocity of a body changes from u to v uniformly (uniform acceleration), then Uniform Velocity If a body covers equal distances in equal time intervals moving in a particular direction, it is said to move with uniform velocity. This motion is called uniform motion. Acceleration The rate of change of velocity of a body is called its acceleration. Its SI unit is m/s2. It is a vector quantity. Equations of motion by graphical method Consider a body uniformly increasing its velocity from u to v in time interval t. In the graph Initial velocity is represented by OA = EC = u Final velocity is represented by OD = BC= v Time is represented by OC = AE = AB = t 1) Acceleration of the body is given by