Newton’s first law of motion states that a body continues to be in the state of rest or in the state of motion until and unless acted upon by some external force. Motion of a body has multiple aspects to it – distance covered, displacement incurred, time taken, speed of motion, force applied to ensure the motion, the direction of motion and much more. Kinematics is a branch of physics where we talk about the spatial or geometrical position of the body while in motion, without considering or talking about the forces involved in the motion of the body. Kinematics does not consider the causes of motion. Let’s learn more about it.
Kinematics comes from Greek word ‘kinemat’ which means motion and Latin word ‘ics’ meaning ‘study of’, therefore making it ‘Study of motion’. With the help of kinematic equations we can calculate multiple aspects of motion including time, displacement, velocity and acceleration.
Displacement is defined as the net difference between the original and the final positions of the moving body.
Time, as the word itself says, is the total time taken for the displacement to occur.
Velocity is defined as the rate at which the body is moving. Mathematical formula is –
v = d / t (v = velocity, d = displacement, t = time)
This also implies that, d = v*t and t = d / v.
Acceleration is defined as the rate at which the velocity of the object is changing. For example, initially when a car starts, its speed is less so net displacement is less. Therefore, the velocity of the car is less. As the speed increases, the displacement increases and hence the velocity increases. This difference in initial velocity and final velocity is the net difference in velocity. When we divide it by time taken, we get the rate at which velocity changes.
a = (v – u) / t
a is the acceleration, v is the final velocity, u is the initial velocity and t is the time taken by the body to reach from ‘u’ to ‘v’.
Example – when a car starts, displacement is 0. So net velocity is 0. Let’s say after 60 seconds, the displacement is 600 meters. Therefore, final velocity is,
v = 600 / 60 = 10 meters per second.
Now acceleration is,
a = (10 – 0) / 60 = 1 / 6 meters per second square.