Mechanics

Linear Motion - Speed, Velocity, Acceleration
Linear Motion is motion in a straight line.

Speed
Speed is defined as the rate at which distance changes with time. In other words,
                                   Speed = Distance
                                                      Time
In many cases a motorist traveling over any distance will be faced with varying traffic conditions to slow down, stop or speed up. By the end of the journey, he would have done an average speed.
                  Average Speed = Total Distance
                                                Total time taken
Traveling from point A to point B, a distance of 144 miles in 2 hrs. would give an average speed of 144/2 = 72 miles/hr.

Velocity
Velocity is speed in a specified direction. It is a vector quantity while speed is a scalar quantity.

Acceleration
Acceleration is the rate of change of velocity with time. Let's say a motorist comes to a stop at point B from a speed of 152 meters per sec. (m/s) in 20 sec. The final velocity then would be 0 m/s. The initial velocity is 152
m/s. Change in velocity = final velocity - initial velocity
                                  = 0 - 152
                                  = -152 m/s
The rate of change of the velocity would be -152/20. That is, -7.6 m/s². The minus sign tells the car is decelerating.

Equations of Motion
A car moving from point A to point B will move in a given time t. The velocity at which it leaves point A is the initial velocity u, while that of reaching point B is the final velocity v. The distance between A and B is given as s and the acceleration, a.

There are three main equations of motion.
                                             1.   v = u + at
                                             2.   s = ut + ¹/₂at²
                                             3.  v² = u² + 2as
Using any of these depends on the information one may have on a given moving body.
                                                                                     Solved Problems
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Newton's Laws of Motion
1. A body continues in its state of rest or of uniform motion in a straight line, unless compelled by some external force to act otherwise.

2. The rate of change of momentum of a body is proportional to the applied force and takes place in the direction in which the force acts.

3. To every action there is an equal and opposite reaction.
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