by Amanda Dcosta

Created on: November 04, 2009   Last Updated: February 11, 2010

The three laws of motion by Sir Isaac Newton changed the face of physics since the mid seventeenth century. In 1687, Newton presented his famous research and deductions in "Principia Mathematica Philosophiae Naturalis" which laid the foundation for modern science and mathematical physics. The three laws of motion, in essence, describe the relationship between mass, inertia, acceleration, momentum and force of a body.

The First Law of Motion: The Law of Inertia

"An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force."

This is to say that all objects remain in their state of rest or their state of motion in one direction unless forced to change by an external agent. It is like saying a ball will roll down a slope and change course only when we make it roll upwards by exerting force on it.

Another apt example would be a picture hanging on a wall. It will stay that way unless external force is applied to it to move it from that position.

The Second Law of Motion:

"Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object)."

This law takes into consideration three elements of an equation; Force (F), Mass (m) and Acceleration (a) in F=m x a.

The greater the mass, the greater the force required to accelerate. It is like saying, how much force is required to moved a 1000 kg object at 0.05 metres/sec/sec ? Force would thereby result as F=m x a or F=ma. The above example would thus read as F = 1000 x 0.05 = 50. The unit of force is Newtons and therefore the result would be 50 Newtons.

This law gives the guidelines to also understanding why it is easier to push a child on a swing rather than an adult.

The Third Law of Motion:

"For every action, there is an equal and opposite reaction."

This is to say that when an object pushes another object with a certain amount of force, it also receives an equal amount of force from that object, making it move in the opposite or reverse direction.

This is the principle used to send a rocket moving upwards. The rocket exerts a force on the ground in order to start moving, and the ground in turn exerts an equal and opposite force on the rocket, sending it upwards.

Sir Isaac Newton completed his work outlining the 'laws of motion' in May 1686. Astronomer Edmund Halley published and printed his (Newton's) findings in 1687.

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