 Newton’s Laws

Sir Isaac Newton, the man who developed the first theories of gravitation, also introduced the three laws of motion. These laws essentially changed the field of physics in an astounding manner – it paved the way for modern science. Let’s look at these laws in some more detail, which is also covered during our JC physics tuition classes:

Newton’s first law:

It states that an object will remain at rest or in a uniform motion, unless an external force acts on it. This is basically also the definition of inertia. In other words, the state of motion of an object will not change unless there’s an external force that acts to change this motion. Therefore, velocity is either zero, or remains constant.

Newton’s second law:

This describes the change in velocity of an object when acted upon by an external force. Thus, the force exerted on an object is equal to the constant mass of the object multiplied by the change in its velocity over time (acceleration). Mass times velocity is also known as momentum. When it is mentioned that momentum changes over time, it is the exact same concept as mass times acceleration. The formula for Newton’s second law is

F = m x a
Where F is force, m is mass and a is the resulting acceleration due to the force changing the velocity. The unit of this equation is in Newtons (N), or kilograms times meters per squared second (kg x m/s2), when using S.I. units. Here’s an example of the formula in use:

If a man pushes a box that has a mass of 1 kg, and the box has a constant acceleration of 2 m/s2, what is the magnitude of the force that the man exerts on the box, ignoring friction?
F = m x a = (1 kg) x (2 m/s2)
F = 2 N

Note that this formula can be applied in three general ways in a test or exam. You can be asked to calculate either F, m or a. By rearranging the formula, it is possible to calculate m or a because, m = F / a  or  a = F / m

Newton’s third law:

The third, and last, law states that for every force exerted, there’s an opposite force of equal magnitude. For example, if object A exerts a force on object B, then object B will exert a force of equal magnitude on object A.

These are the three simple motion laws of Newton which will remain the building blocks of modern physics. If you decide to continue physics or physics related courses in school or university, these laws will apply to most motion equations that you will study. Therefore it’s very important to understand, and be able to apply, these laws in your studies.