Newton’s Laws of Motion - 1Newton’s Laws of Motion - 1

Describes the relationship between the motion of objects in our everyday world and the forces acting on them.

Conditions when Classical Mechanics does not apply:

- Very small objects (< atomic sizes)- Objects moving near the speed of light

Classical Mechanics

Forces

Simple definition: a force is a push or pull on some object.

Force is a vector quantity.

Distunguish:contact forces and remote (“action at a distance” or “field” forces.

Contact forces result from physical contact between two objects.

Field forces act between disconnected objects.

Examples of Contact and Field Forces

The Four Fundamental Forces

In order of decreasing strength: Strong nuclear force

Electromagnetic force Weak nuclear force Gravity

All are field forces.Only gravity and electromagnetic forces are treated in classical mechanics.

Lex 1: Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum,nisi quatenus a viribus impressiscogitur statum illum mutare.

Law 1: Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by

forces impressed upon it.

Law 1: Every body continues in its state of rest, or of uniform motion in a straight line, unless it is compelled to change that state by

forces impressed upon it.

This is sometimes called the law of inertia.

Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur.

The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body.

Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur.

The acceleration produced by a particular force acting on a body is directly proportional to the magnitude of the force and inversely proportional to the mass of the body.

Fa

m

Second Law:F

am

is in the direction of

1

a F

a F

am

1. The acceleration vector is in the direction of the net force.

1.

Second Law:F

am

is in the direction of

1

a F

a F

am

2. The magnitude of the acceleration vector is proportional to the magnitude of the net force.

2.

Second Law:F

am

is in the direction of

1

a F

a F

am

3. The magnitude of the acceleration vector is inversely proportional to the mass.

3.

The SI unit for force:

The force that gives an object of 1 kg mass an acceleration of 1 m/s2 is defined as

1 newton (N).

1 N = 1 kg.m/s2