FORCES

KinematicsThe study of how objects move

DynamicsThe study why objects move as they

do.

Kinds of ForcesGravitational Force:

Attractive force that exists between all objects. The gravitational force between the Earth and the moon keeps the moon in orbit. It may be the most evident but it is the weakest of all the forces.Electromagnetic Force:

Charged particles at rest or in motion exert electric forces on each other. They give materials their strength, their ability to bend, squeeze, stretch or shatter. When charged particles are in motion they produce magnetic forces on each other. Electric and magnetic forces are both considered to be aspects of this single force.

electron

neutron

proton

Kinds of Forces

Strong Nuclear Force:A strong force that holds the particles of the nucleus of an atom together. Short range attractive force that is much larger in magnitude to the gravitational or the electromagnetic forces.

Weak Force:Force involved in transmutation of particles within the nucleus. Only observed/viewed in radioactive decay. Stronger only than the gravitational force.

History LessonAristotle (384-322 B.C.)

Natural MotionObjects seek their natural resting places

- Boulders fall, Smoke rises

Heavenly bodies move in perfect circles around the EarthViolent Motion

Imposed Force

Some external cause i.e.. Wind on a ship

Greek Philosopher and scientist, student of Plato and the tutor of Alexander the Great.

Two Types of Motion

If an object is in motion “Against its nature” then some kind of force is responsible

Earth not moving, is in its natural resting placeWorked for 2

000 years

First to state that a force causes

motion

Nikolaus Copernicus (1473-1543)

Polish Astronomer who demonstrated that the Earth rotates on its axis and that the planets revolve around the sun

Heliocentrist – Belief in the sun centered model of the solar system. Prior belief was the geocentric model, with the Earth as

the center of the universe

Received his publication “ De Revolutionibus” the day he died May 24th 1543

Galileo Galilei (1564-1642)Italian astronomer,

physicist, mathematician, and inventor Tried and convicted of heresy for

his beliefs in the Heliocentric- Copernican model of the solar system

First to define a FORCE as a Push or PullForce is not necessary to keep an object in motion

Friction is a type of force, caused by irregularities in the surface of objects that are in contact. When friction is present a continual contact force is needed to keep an object in motion.

So why do objects come to rest? FRICTION

Galileo believed and showed that “Experiment” not “Logic” was the best test of knowledgeGalileo’s ideas discredited Aristotle and many ancient

philosophiesHe died the year that Newton was born 1642

Sir Isaac Newton (1642-1727)

Born in England on Christmas day 1642

Never knew his father, As a young lad lived with his mother on their family farm

Had few friends and was not a stellar student but was very bright

A family friend recognized his intelligence and

helped him to get into Trinity College, Cambridge

University

In 1665 the Bubonic In 1665 the Bubonic Plague reached Plague reached

Cambridge and the Cambridge and the University was University was

closedclosedNewton went back to his family farm and

continued to study on his own.

It was during this time that he

devised a number of scientific

principles that we still adhere to

todayThree Laws of Motion

Theory on colored light

Fluxions – Better known as Calculus

The law of Gravity

Three Laws of Motion

Newton’s First Law of Motion“Law of inertia”

An object will remain in it’s state of motion unless a force acts upon it.

Inertia = The reluctance of a body to change it’s state of motion.

Mass is a measure of inertiaA Body at rest `tends to stay at rest

A Body in motion tends to stay in motion

Newton’s Second Law of MotionThe acceleration produced by a net force on an object

is directly proportional to the magnitude of the net force (in the same direction as the net force), and is inversely proportional to the mass of the object.

Acceleration= Net Force/ Mass

F=ma

a =

Fm

Newton’s Third Law of MotionWhenever one object exerts a force on a

second object, the second object exerts an equal and opposite force on the first object.

Action – Reaction Law Hammer & Nail

The hammer exerts a force on the nail to drive it into the block. The nail must exert a force on the hammer to halt it in the process

Force is an interaction between

objectsInteraction always occur in pairs

Horse and Horse and CartCart

A horse has some understanding of physics. He knows Newton’s third law. For every force applied there is an equal but opposite force.

So, he knows that no matter how hard he pulls the cart, the cart will pull back on him with the same force, opposite in direction. The forces must be balanced. Hence no acceleration. So why pull?

Its actually Newton’s Second Law that

determines if the cart accelerates

All the forces on the cartcart must be identified

1. The pull of the horse is only one force

2. The friction between the cart and the ground is

another

If the Horse can pull on the cart more than the friction applied between the cart and the ground,the cart will accelerate

If unbalanced net force is

present than the

cart accelerates