A force is a push or a pull that one object exerts on another which produces, or tends to produce, stops or tends to stop motion. A force can also change the shape of an object.
The SI unit for force is newton (N), with 1N being the approximate amount of force that the earth pulls on an object of mass 100g. A force is a vector quantity, with a magnitude and direction.
Scalar quantities are physical quantities that have a magnitude (size) only. A vector is a physical quantity with a magnitude and a direction. The addition of vectors must not only take in account the magnitude, but also the direction of the vectors. When we add two vectors, we mean to find a single vector with the same effect. The single vector is sometimes called the resultant.