If a particle is moving in a straight line under a constant acceleration, then relations between its velocity, displacement, time and acceleration are represented by the following equations: $x^2$ (1) v = u + at (2) s = ut + (1/2)at² (3) v² - u² = 2as Where: S = Displacement v = Velocity a = Acceleration t = Time taken

Scalar Quantity: A quantity, in which direction is not important, i.e. only magnitude is important is called scalar quantity. e.g. speed, distance etc.

Vector Quantity: A quantity, in which direction as well as magnitude are important is called a vector quantity. e.g. velocity, displacement etc.

Speed: Distance covered by a body per unit time is called speed.

S = D / T

Where
      S = Speed of the body.
      D = Distance travelled by the body.
      T = Time taken

This is most talked about law in the Newton's Laws of Motion. This law states that:

If a force is applied on a body, it applies an
 equal and opposite force.

This law is also generally stated in short as:

Every action has an equal and opposite reaction.

What is so big deal about this law? In fact, there is. Many of the modern day equipments use this law for their working.

For example a rocket:

Various types of constants have been defined in physics, which we use for performing various calculations. These constants are from various branches of science and are mostly universal in nature. (Except some like acceleration due to gravity on Earth, which changes from place to place).

Newton's Second law of motion is very important specially relating to the calculations involving force and motion. This is the basic law relating the force applied on an object and the resultant acceleration gained by that object. So, this law has become a basis of many theories and laws proposed in the Physics.

This law states that:

Force applied on a object is directly proportional to the
acceleration acquired by it.

Putting constant k along with mass m, we get:

According to Newton's First law of motion:


Any object at rest or in uniform motion remains at rest or in uniform motion unless a force is applied on it.

What this definition really means is that any body will not change its status of rest or of uniform motion unless a force is applied on it.

For example, a ball lying on the table at rest will remain there at rest unless someone sets it rolling by applying force.

Similarly, a ball already rolling will keep rolling unless someone stops it by applying force.