Newtonian Newtonian MechanicsMechanics

Corpus omne persevare in Corpus omne persevare in status suo quiescendi vel status suo quiescendi vel movendi uniformiter in movendi uniformiter in directum nisi quantenus illud directum nisi quantenus illud a viribus impressis cogitur a viribus impressis cogitur statum suum mutare.statum suum mutare.

Newton’s First LawNewton’s First Law

Every body continues in its state of rest Every body continues in its state of rest or uniform motion in a straight line unless or uniform motion in a straight line unless compelled by an external force to change compelled by an external force to change that state.that state.

Galileo and the Law of Galileo and the Law of InertiaInertia

Galileo looked at motion differently.Galileo looked at motion differently. If you push an object across a surface, the If you push an object across a surface, the

smoothness or lubrication on the surface smoothness or lubrication on the surface affects how hard you have to push the object to affects how hard you have to push the object to keep the object moving.keep the object moving.

As the surface gets slicker and slicker, the As the surface gets slicker and slicker, the force required gets smaller. Eventually, the force required gets smaller. Eventually, the force required to keep the object moving would force required to keep the object moving would decrease to zero. This leads to:decrease to zero. This leads to:

The Law of InertiaThe Law of Inertia

The Law of Inertia states that a body The Law of Inertia states that a body once set in motion and thereafter once set in motion and thereafter undisturbed will continue in uniform undisturbed will continue in uniform motion forever, all by itself.motion forever, all by itself.

This can be simplified to, “An object This can be simplified to, “An object continues doing what it is already doing.”continues doing what it is already doing.”

Newton add to the Law of Newton add to the Law of InertiaInertia

Newton used Galileo’s Law of Inertia as Newton used Galileo’s Law of Inertia as the basis for his first law that was the basis for his first law that was published in his 1687 work, Principia published in his 1687 work, Principia Mathematical Principles of Natural Mathematical Principles of Natural Philosphy.Philosphy.

Newton extended this law with other Newton extended this law with other laws of motion.laws of motion.

Newton’s LifeNewton’s Life

Born December 25, 1642Born December 25, 1642 Gregorian calendar January 4, 1643 but it was Gregorian calendar January 4, 1643 but it was

not adopted until 1752.not adopted until 1752. Started Trinity College June 1661 and wanted Started Trinity College June 1661 and wanted

to be a lawyer.to be a lawyer. The plague closed Cambridge for two years The plague closed Cambridge for two years

starting in 1665. Newton did work at home.starting in 1665. Newton did work at home. Appointed to the Lucasian Chair in 1669.Appointed to the Lucasian Chair in 1669.

More on NewtonMore on Newton

1687 published Philosophiae Naturalis 1687 published Philosophiae Naturalis Principia MathematicaPrincipia Mathematica

1693 had a nervous breakdown1693 had a nervous breakdown 1696 appointed Warden of the Royal Mint1696 appointed Warden of the Royal Mint 1699 appointed Master of the Royal Mint1699 appointed Master of the Royal Mint 1703 elected president of the Royal Society1703 elected president of the Royal Society 1708 Knighted1708 Knighted 1727 died1727 died

Inertia and MassInertia and Mass

So strong is our belief in the Law of Inertia, we So strong is our belief in the Law of Inertia, we try to use inertia reference frames.try to use inertia reference frames.

Inertial reference frames are frames of Inertial reference frames are frames of reference where the Law of Inertia does work.reference where the Law of Inertia does work.

The rotating frame of reference is an example The rotating frame of reference is an example of a not inertial reference frame. Our minds of a not inertial reference frame. Our minds start to create forces to explain apparent start to create forces to explain apparent deviations from the expected motions.deviations from the expected motions.

A Word About ForcesA Word About Forces

Forces are defined as a push or pull on Forces are defined as a push or pull on an object.an object.

Forces are vector quantities.Forces are vector quantities. In the Metric System of measurement, In the Metric System of measurement,

forces are measured in Newtons (N).forces are measured in Newtons (N). 1 N = 1 kg1 N = 1 kg·m/s²·m/s²

The Fundamental ForcesThe Fundamental Forces

There are four fundamental forces in Nature. There are four fundamental forces in Nature. All other forces are really combinations of the All other forces are really combinations of the four fundamental forces.four fundamental forces.

The four fundamental forces are:The four fundamental forces are: GravityGravity Electric-Magnetic ForceElectric-Magnetic Force Strong Nuclear ForceStrong Nuclear Force Weak Nuclear ForceWeak Nuclear Force

Force of GravityForce of Gravity

The force of attraction between any two The force of attraction between any two masses.masses.

This force is proportional to the product This force is proportional to the product of the masses and is inversely of the masses and is inversely proportional to the square of the distance proportional to the square of the distance between the masses.between the masses.

Electric ForceElectric Force

The electric and the magnetic force are The electric and the magnetic force are two different aspects of the same force.two different aspects of the same force.

The electric force can be an attractive or The electric force can be an attractive or a repulsive force and depends on the a repulsive force and depends on the charges involved and the distance charges involved and the distance between the charges.between the charges.

Strong Nuclear ForceStrong Nuclear Force

The strong nuclear force is the attractive The strong nuclear force is the attractive force between two nucleons (neutrons or force between two nucleons (neutrons or protons). protons).

The strong nuclear force is responsible The strong nuclear force is responsible for holding the nucleus of an atom for holding the nucleus of an atom together.together.

Weak Nuclear ForceWeak Nuclear Force

The weak nuclear force is a repulsive The weak nuclear force is a repulsive force that is responsible for radioactivity.force that is responsible for radioactivity.

““Common” ForcesCommon” Forces

Normal ForceNormal Force The force a surface exerts on an object.The force a surface exerts on an object. The normal force is perpendicular to the surface.The normal force is perpendicular to the surface. TensionTension The force that is exerted by a rope, string, cable etc. The force that is exerted by a rope, string, cable etc.

on an object.on an object. Remember, you can’t push with a rope.Remember, you can’t push with a rope. Elastic ForceElastic Force The force exerted by stretching or compressing an The force exerted by stretching or compressing an

elastic object.elastic object.

More “Common” ForcesMore “Common” Forces

FrictionFriction The force between two surfaces acting The force between two surfaces acting

parallel to the surface.parallel to the surface. BuoyancyBuoyancy The force a fluid applies to an object due The force a fluid applies to an object due

to differences in density.to differences in density.

Units of ForceUnits of Force

In the SI system, forces are measured in In the SI system, forces are measured in Newtons (N).Newtons (N).

A Newton is equivalent to a A Newton is equivalent to a kilogram·metre/second².kilogram·metre/second².

1 N = 1 kgm/s²1 N = 1 kgm/s²