Kinematics is the science of describing the motion of objects using words, diagrams, numbers, graphs, and equations.
Distance and Displacement
Consider a friend tells us that there is a treasure about 5 kilometers away from here. It is only a piece of partial information because with this information we can't reach the treasure, as don't know in which direction we need to travel. This is called distance,
It is single-dimensional information and hence called a scaler
But if the friend tells us 'there is a treasure about 5 kilometers north from here', then we have higher chances to reach the treasure because we know in which direction we need to travel. This is called displacement
, it is two-dimensional information (length and direction), hence called a Vector
Speed and Velocity
Consider a car is 20 Km away from the post office and it is moving at 40 Km per hour. With this information, we can't predict that when it would reach the post office because we don't know it is moving toward the post office or going in some other direction. The 40 Km/hour is called speed of car, it is single-dimensional and scalar.
If we know the direction of movement like 'car is moving at the speed of 40 kilometers towards post office', then we can say that it could reach to the post office in half an hour. It is called velocity, it is two-dimensional and Vector
Formula : distance traveled per unit time.
Speed = (distance)/(time)
unti = m/s or ms-1
Types of speed Average speed
: the total distance traveled in total time. Or the average of initial and final velocity.
Average velocity = (total distance)/(total time) or (initial velocity + final velocity)/2 Uniform speed
: If an object is moving with constant speed then it is called uniform speed. Non-uniform speed
: If the speed of an object change with time then it is called non-uniform or variable speed.
The increase of velocity per unit time is called Acceleration
, and the decrease of velocity per unit time is called deceleration
. This means the deceleration is actually a negative acceleration.
Acceleration = (change in velocity)/time or (v2
)/t or (v - u)/t where v1
or u is initial velocity and v2
or v is final velocity.
unit = meter per square second, m/s2
(As the unit of velocity is m/s when it divides by unit of time so it becomes m/s2
Types of Acceleration Uniform Acceleration
: When the velocity of an object change in equal amounts in equal time intervals then is it called uniform acceleration. Non-Uniform Acceleration
: When the velocity of an object changes in non-equal amounts in equal time intervals then is it called non-uniform acceleration.
- When an object starts from rest its initial velocity (v1 or u) is 0
- When an object comes to rest its final velocity (v2 or v) is 0
- If an object is thrown upward, then at the highest point its velocity becomes 0 (after that, it start to fall)
- If an object falls freely, then its starting velocity is zero.
- If an object is thrown upward, then
- Time is taken to reach max height = Time taken to reach back to the original position