Forces Today’s Goal: 1.Describe and give examples of the law of inertia and understand that inertia is a basic property of matter

Sir Isaac Newton English “natural philosopher” (what we would call a scientist. Famous apple Published in 1687 The Philosophiae naturalis principia mathematica, commonly known as the Principia In the King’s English: The Mathematic Principles of Natural Philosophy

The Principia First publication of its kind; nobody had ever treated science so rigorously In order to adequately describe nature, Newton invented Calculus at the same time Laid out the fundamental principles of Classical Physics which dominated science until the advent of Quantum Mechanics in the 1920’s

Newton Also developed the science of optics Was knighted (the first scientist to be so honored) “If I have seen so far, it is because I stood on the shoulders of Giants.”

Mass The quantity of matter – how much stuff something is made of On a fundamental level dependent on the number of atoms that make something up SI Unit : kilograms An object’s mass can only be changed by changing the object (breaking it, cutting, etc)

Forces A force is any action that is capable of accelerating an object – that is capable of changing the motion of an object Push or pull Forces are vectors; meaning they have magnitude and direction Symbol: F sandtime/force/ sandtime/force/

Newton’s Second Law The acceleration of an object is proportional to the net force acting on the object and is inversely proportional to the mass of the object. Net force – sum of all forces acting on an object.

Newton’s First Law So what if no net force acts on an object? –The object continues in motion in a straight line with constant velocity (the acceleration is zero) –If it’s at rest, it stays at rest. Inertia: the tendency of any object to resist changes in its motion Equilibrium – state when the net force acting on an object is zero

Newton’s First Law “Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon.” Newton

Newton’s First Law The idea that an object keeps moving forever in a straight line is contrary to what you see. This is because every object that you encounter on a daily basis is stopped by friction or drag.

Newton’s Third Law Forces always occur in pairs When you push on something, it pushes back. This force is called a reaction force. The reaction force is equal in magnitude to the original force & opposite in direction.

Measuring Force Forces can be measured with springs or other elastic objects (such as rubber bands) SI Unit: Newton (N) English Unit: Pound (lbs) 1 lb = 4.4 N Another unit: ton 1 ton = 2000 lbs

Force Magnitudes Force (N)Force (lbs) Refrigerator magnet102.3 Weight of a person Force on jet pilot during takeoff Force generated during space shuttle launch 140,00035,000

Two Kinds of Forces Long – range forces – act over distances between two objects Contact forces – force between two objects in direct contact What are some examples of each?

Four Fundamental Forces 1.Gravity – acts over distances between two objects 2.Electromagnetic – responsible for all the forces you encounter except gravity – force between charged particles 3.Weak Nuclear Force 4.Strong Nuclear Force Hold nucleus of atoms together: very short range

Forces You Should Know Gravity (F g ) – the force of attraction between two objects: also known as weight Tension (F T ) – the force that holds a string or rope together Friction (F f ) – force caused by surfaces rubbing together; acts to oppose relative motion Normal (F N ) – reaction force of a surface on anything pushing on it

Forces You Should Know Drag (F D ) – force of a fluid exerted on anything moving through it (air resistance) Thrust (F T ) – force from engines, rockets, etc. that propel an object forward Lift (F L ) – Upward force that causes airplanes and other flying objects to fly

GRAVITY GRAVITY: An attraction force between all masses Newton’s universal law of gravitation Newton’s universal law of gravitation: Every object in the universe exerts a gravitational attraction to all other objects in the universe The amount of gravitational force depends upon the mass of the objects and the distance between the objects What is Gravity?

Mass vs. Weight Mass – the measure of how much matter an object possess Weight – a measure of how strongly the Earth (or whatever planet an object is on) pulls the object down: same as saying “force of gravity” Mass and Weight ARE NOT THE SAME!!

Mass vs. Weight Mass can only be changed by adding or removing matter from the object Weight can be changed by moving to a different planet, or by changing the mass Weight is dependant on the mass of an object and the acceleration due to gravity, which changes from place to place.