Born in 1642, at a time of great political turmoil in the UK, Sir Isaac Newton was a British scientist whom many regard as the greatest physicist of all time perhaps because of the tremendous effect that knowledge of his three laws have had on our world ever since he proposed them. Before Newton’s laws it was Aristotle’s description of the physical universe that had been broadly accepted but it had proved inadequate to describe the true nature of movement.
Newton worked on the problem for some time and devised three general rules about the movement of objects which were published in 1686 (when he was just 24 years old) and have come to be known as Newton’s Three Laws of Motion. Together with his theory of gravitation, they were regarded as ‘laying down the entire foundation for classical mechanics’.
The First Law of Motion
All objects resist changes in their state of motion so this law states that every object will remain at rest, or in uniform motion in a straight line, with the same direction and speed, unless compelled to change its state by the action of an external force. This is normally taken as the definition of ‘inertia’ – an unchanging state. In other words, if nothing is happening to you, you’ll simply stay the same. And if you’re going in a specific direction, you will go in that direction forever, unless something happens to change your course. It takes an external force (e.g electrical, magnetic, gravitational, or something with tension, friction or resistance) to change your situation. This first law simply shows that objects will just keep doing what they are doing forever in time until forcibly changed by something else.
It is easy to try this out with a cup of tea in your car. If you begin to drive your car, while the car accelerates forward, the tea will try to stay in the same restful state, no matter what the car is doing, or how difficult that might be with the increased movement. However, if the car accelerates out from under the tea (the external force) the tea is likely to spill in your lap. Another example is that of pushing a child in a swing. It is much easier than trying to push an adult because the adult would have more intertia.
The Second Law of Motion
This proposes that the acceleration(a) of an object produced by applied force(f) is directly related to the magnitude(m) of the force. Thus the relationship between an object’s mass, its acceleration and the applied force can be easily calculated by using the formula F = ma. This law shows that if you exert the same force on two objects of different mass, you will get different accelerations (changes in motion). The effect (acceleration) on the smaller mass will be greater and more noticeable. In the simplest terms, this law demonstrates that heavier objects need more force to move the same distance as lighter ones.
This can easily be tested in sports where the size and weight of the balls involved will need varying degrees of push and force behind them to maintain the same acceleration and momentum as each other. That is why a soccer ball (being lighter) wlll accelerate more than a bowling ball when thrown with the same force.
The Third Law of Motion
This states that for every action (force) there is an equal and opposite reaction (force) . Forces are found in pairs because of the need for symmetry, hence forces in action always encounter other forces acting in the opposite direction. In simple terms, whenever one object pushes another, it gets pushed back in the opposite direction equally hard! If that did not happen, the first object would not make any progress in whatever it is doing. It would always be frustrated in its action.
For example, take the every day act of sitting in a chair. Your body exerts a downward force to sit, but the chair needs to exert an equal upward force to contain your weight, otherwise it would collapse! Another great example is shooting a cannonball. When the cannonball is fired through the air by the explosion, the cannon is pushed backward. Though the force pushing out the ball was equal to the force pushing back the cannon, the true effect on the cannon is less noticeable because it has a much larger mass.
These three laws have enabled greater understanding of mechanics, and the way nature works, creating some innovative changes in our lives, especially in the travel and space industries. In fact, they have become such an integral part of our existence, we often do them without even thinking!
Sir Isaac Newton lived to the ripe age of 85 and was able to see some very useful applications of his laws.
Sources
http://www.grc.nasa.gov/WWW/K-12/airplane/newton.html
http://www.sciencemaster.com/jump/physical/newton_law.php
http://teachertech.rice.edu/Participants/louviere/Newton/laws.html
