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HONORS 227 1 September 2015 Dr. Harold Geller College of Science School of Physics, Astronomy and Computational Sciences George Mason University 1 Chapters 1 and 2 and Other Stuff • A Personal Response System (iClickers) • Units of length, mass and time • Metric Prefixes • Chapter 2 and the Ordered Universe 2 • The basic unit of angular measure is the degree (°). 3 Angular Measurements • Subdivide one degree into 60 arcminutes – minutes of arc – abbreviated as 60 arcmin or 60´ • Subdivide one arcminute into 60 arcseconds – seconds of arc – abbreviated as 60 arcsec or 60” 1° = 60 arcmin = 60´ 1´ = 60 arcsec = 60” 4 Powers-of-ten notation is a useful shorthand system for writing numbers 5 Common Prefixes for Powers of Ten Factor (billion) 109 (million) 106 (thousand) 103 (hundredth) 10-2 (thousandth) 10-3 (millionth) 10-6 (billionth) 10-9 Name Symbol Giga- G Mega- M kilo- k centi- c milli- m micro- nano- n 6 Astronomical distances are often measured in astronomical units, lightyears or parsecs • Astronomical Unit (AU) – One AU is the average distance between Earth and the Sun – 1.496 X 108 km or 92.96 million miles • Light Year (ly) – One ly is the distance light can travel in one year at a speed of about 3 x 105 km/s or 186,000 miles/s – 9.46 X 1012 km or 63,240 AU • Parsec (pc) – the distance at which 1 AU subtends an angle of 1 arcsec or the distance from which Earth would appear to be one arcsecond from the Sun – 1 pc = 3.09 × 1013 km = 3.26 ly 7 Science is an adventure of the human mind 8 HNRS 227 Chapter 2 – Ordered Universe 9 Main Concepts I will focus Upon from Chapter 2 • • • • • • • • Speed vs. Velocity Acceleration Force Falling Objects Newton’s Laws of Motion Momentum Angular Momentum Universal Law of Gravity 10 Speed and Velocity • Speed – distance traveled in a unit of time – a scalar quantity • Velocity – speed and direction – a vector quantity 11 Force • Definition of force – something that causes a change in the motion of an object • a push or pull • an electric, magnetic, gravitational effect • a vector quantity • Net force - Resultant Force 12 Inertia • Defining Inertia – tendency of an object to remain in its current state of motion • the more massive the more inertia • think of stopping a car vs. truck 13 Acceleration Due to Gravity • Direction of acceleration due to gravity – directed to center of Earth • Think: scalar or vector? • Why? 14 Generalized Motion • Motion can be viewed as a combination of movements – vertical component • typically gravitational acceleration – horizontal component • some force from muscle, gunpowder, etc. 15 Question for Thought • Do you recall what inertia is? 16 Question for Thought • Where does the unit s2 (or concept of “square second”) come from? 17 Newton’s Laws of Motion • Newton’s First Law of Motion – body at rest tends to stay at rest and body in uniform motion will stay in straight line uniform motion unless acted upon by an outside force • Newton’s Second Law of Motion – the acceleration of a body is proportional to the force being applied –F = m*a 18 Newton’s Laws of Motion • Newton’s Third Law of Motion – for every force there is an equal and opposite force (action and reaction) 19 Question for Thought • How can there ever be an unbalanced force on an object if every action has an equal and opposite reaction? 20 Momentum • By definition momentum is the product of – mass and velocity • Conservation of momentum –total momentum of a closed system remains constant 21 Angular Momentum • Torque – Twisting force • Conservation of Angular Momentum – “an object that is rotating will keep rotating unless a twisting force called a torque acts to make it stop” – Applications include • Ice skater • Inertial guidance systems 22 Universal Law of Gravity • Newton’s Universal Law of Gravitational Attraction – every object is attracted to every other object – the force is proportional to masses and inversely proportional to the distance squared »F = (G*m*M) / r2 23