Essay Sir Isaac Newton's Three Laws of Motion

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We have all heard the story of the apple falling on Newton's head while he was sitting against the tree, thus

giving him the sudden idea for the Universal Law of Gravity. This, as I am sure most of us know, is not really

what happened. A more accurate version would probably be, Newton observed an apple falling from a tree

and started contemplating the physics of the apple's fall. The acceleration experienced by the apple, which

started at zero when hanging in the tree, then increased as the apple fell. This as Newton reasoned from his

second law of motion, means there must be a force acting upon the apple in order to cause the acceleration,

this force we will call gravity. Thus giving us the acceleration due to this force
From this we are able to tell that

if an object is either accelerating or decelerating than an external force must be acting on it even if it is

simply the force of gravity, air resistance, or friction.

Newton's 2nd Law

This is probably the most known of all three of Newton's Laws of motion.

* The acceleration of an object is directly proportional to the net force

acting on it, while being inversely proportional to its mass.

More often though we see this law written as;

Fnet = ma

Where "F" equals the net force on the object in Newtons, "m" equals the mass in kilograms and

"a" equals the acceleration of the object in meters/second^2. Since force is a vector this can be

rewritten in three separate equations to take into account direction;

Fx = ma, Fy = ma, Fz = ma

Fnet = Fx + FY+ Fz

We must also remember that acceleration as well is a vector and therefor has three components just

like the force. When learning how to use Newton's 2nd Law, however, one usually only uses examples

where there is only two directional forces acting on an object. These are usually the x-direction (side

to side) and the y-direction (up and down). For now we are only going to take into account these two

components.

This law is very useful in the fact we can determine the acceleration of an object if we know the forces

acting on it as well as it's