What is Newton's Second Law (F = ma)?

In short

Newton's second law says that the net force on an object equals its mass multiplied by its acceleration, $F = ma$ . The acceleration is in the direction of the net force.

In simple words

The force is in newtons (N), the mass is in kilograms and the acceleration is in $\text{m/s}^2$ . One newton is the force that gives a mass of $1\ \text{kg}$ an acceleration of $1\ \text{m/s}^2$ . The law uses the net force, the sum of all forces on the object. A bigger mass needs a bigger force for the same acceleration. F stands for force, m for mass and a for acceleration.

Example

A $2.0\ \text{kg}$ trolley is pushed with a net force of $6.0\ \text{N}$ . Its acceleration is $a = \dfrac{6.0\ \text{N}}{2.0\ \text{kg}} = 3.0\ \text{m/s}^2$ .

Also searched as: what does f ma stand for, second law of motion.