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Newton's Laws Of Motion



Newton's Laws Of Motion

Sir Isaac Newton was born in 1642 and died in 1727.

It is said that his contributions in pure mathematics, theoretical physics and experimental physics had never ben surpassed until the time of Einstein.

He devoted much of his energy to history, theology, chemistry, alchemy and politics and gave up science at 54 years old.

He had made his three greatest discoveries;

  • Calculus
  • The Theory of Gravitation and
  • The Spectrum of light

by the time he was 24 years old.

Through 1665 - 1667, while the university was closed because of the plague, Newton composed his Principia which is claimed to be the 'most concentrated intellectual effort made by man'.

Fascinated with optics he was able to grind lenses which he used in the telescopes he made.

Through this hobby he discovered that white light was made up of all the colours of the spectrum.

Newton's 1st law of motion states that:

A body is incapable of changing it's condition of rest, or of motion in a straight line at a constant speed, unless it is 'persuaded' to do so by some external force.

One way of looking at this law is by the use of a raw egg and a hard boiled egg.
Mark the eggs and get a friend to help you with the experiment.

Taking an egg each, spin them at a predermined signal and, at another signal, put your fingers on the eggs to stop them.

You will notice that the hard boiled egg will remain at rest while the raw egg will begin to spin again.

The force that brought the eggs to rest was the friction caused by your finger.

As the shell and the liquid inside the raw egg move separately the swirling fluid starts it spinning again.

Newton's 2nd law of motion states that:

The rate of change of the quantity of motion in a body is proportional to the impressed force and takes place in the direction of the impressed force.

Before we get into looking at Newton's second law we are going to build a load bearing ramp from a piece of paper.

Take an A4 sheet of typing or copy paper and fold it down the centre along the longest side.

Fold the paper, in the same direction, as the cross section A, above.
Run some adhesive tape across the two loose 'legs' to stop the ramp flattening out with the load.


In a container (a foam coffee or milk shake container or similar) cut a doorway near the bottom capable of allowing a marble to come off the end of the ramp and enter the container.

Run the ramp from the top of a book/s about 5cm (2") high down to the little door on your container.

Roll one marble down the ramp into the container and note the distance it moves.

Now roll two marbles down the ramp and note the distance the container moves.

Since it takes twice the force to move the two marbles at the same acceleration as one marble it takes twice as much force to decelerate them until they have stopped.

The cup was pushing on the two marbles with exactly the same force as the one marble so with the two the cup had to push longer.

The ultimate stopping force here, by the way, was the friction of the bottom of the container on the surface it stood upon.

Newton's 3rd law of motion states that:

To every action there is an equal and opposite reaction.

Hero's Engine

liquid flow - cup movement - gravity

To view Newton's third law of motion you might make a Hero's Engine as shown above (Not a real Hero's engine, by the way.)

You will need a foam coffee or milk shake container, some string and two bendy drinking straws and a pencil.
Near the bottom of the cup poke two holes with your pencil just a little smaller than the straws.

Snip the long ends of the straws so that the straws on either side of the bendy bits are the same length and insert them into the holes, as above.

Above these holes punch two more just under the beaded lip and tie a piece of string loosely across. To the centre of this 'handle' tie a longer piece, say a metre or so.

Unless you have very understanding adults take your Hero's Engine outside and suspend it by the long bit of string to something like a tree or clothes line.

Fill your container with water and watch it rotate as it empties.

You are watching gravity attempting to drag your engine to the ground. As the engine is secured and won't move gravity settles for taking all the water and is pulling it down.

As the water spurts out through your straws in one direction Newton's third law is working in the opposite direction.


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Published by Robin A Cartledge ~ ABN 19 924 273 138 ~ Low Head, Tasmania ~ Contact/Comment