As what I have learned in my five-year-journey of engineering, Mechanics is the field of Physics that studies the motion of objects. On the other hand, Kinematics deals with the quantitative description of motion, while Dynamics focuses on the forces that affect motion.
In this session, we will differentiate speed from velocity, define acceleration, tackle the graphical representation of motion, and solve some problems using the equations of motion.
Speed vs Velocity
I am sure enough that you already heard the terms "speed" and "velocity". Speed is the measure of how fast an object travels. If an object moves from one position to another in a measured time, its average speed v is obtained by dividing the distance d traveled by the time t taken to cover the distance.
and t is the time in seconds; all in SI units.
Example Problem:
A boy ran a distance of 100 m in 10 s. What was his speed?
A speedometer gives readings of an instantaneous speed.
In physics, instantaneous speed is the speed of a body at a certain instance of time. Cars and other vehicles are the best examples for instantaneous speed. If the instantaneous speed does not change at any moment, then the object is said to move at constant speed.
For some instances, a pilot on an airplane, the direction of motion is just as important as speed. Speed in a given direction is called velocity. Velocity is a vector quantity and is defined as the rate of change of displacement.
Example Problem:
A car traveled 100 km North in 1 hr. What was the car's velocity?
Acceleration
It is often that an object moves at a constant speed, nor remain in the same direction. So, it is very important to specify both the magnitude and direction of a moving object by describing its velocity. Wikipedia defines Acceleration as the rate of change of velocity of an object with respect to time. For example, when a car is moving in a fixed direction picks up speed at the start of the journey and slows down when coming to stop, its velocity is not constant; and it is called an acceleration.
The car traveling along a straight line but with changing speed is said to be accelerating because its velocity is changing over time. Considering that v is the velocity of the car at some instance of time t and v2 is its velocity at some later instance t2, the average acceleration during the two time interval is
Acceleration is expressed as a unit of velocity divided by a unit of time. If v is in m/s and t is in s, then the unit of acceleration is
There is also a term of deceleration. Deceleration is the reduction in speed or rate. It is a negative acceleration.
Example Problem:
A man is biking at a constant acceleration of 15 m/s for 5 seconds. What was his acceleration in that time?
Distance-Time Graph
Motion graphs are useful tools that can tell you how far a body has travelled, how fast it is moving, and all the speed changes take place.
To measure the distance covered by a moving body from a starting position, say, every second, and then plot the values of the distances covered against the corresponding time readings, one obtains a distance-time graph.
Some useful problems from the internet:
@mikekenlytungal
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