1 HONORS September 2015 Dr. Harold Geller College of Science School of Physics, Astronomy and Computational Sciences George Mason University

2 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

3 The basic unit of angular measure is the degree (°).

4 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”

5 Powers-of-ten notation is a useful shorthand system for writing numbers

6 Common Prefixes for Powers of Ten FactorNameSymbol (billion) 10 9 Giga-G (million) 10 6 Mega-M (thousand) 10 3 kilo-k (hundredth) centi-c (thousandth) milli-m (millionth) micro-  (billionth) nano-n

7 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 10 8 km or million miles Light Year (ly) –One ly is the distance light can travel in one year at a speed of about 3 x 10 5 km/s or 186,000 miles/s –9.46 X 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 × km = 3.26 ly

8 Science is an adventure of the human mind

9 HNRS 227 Chapter 2 – Ordered Universe

10 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

11 Speed and Velocity Speed –distance traveled in a unit of time –a scalar quantity Velocity –speed and direction –a vector quantity

12 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

13 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

14 Acceleration Due to Gravity Direction of acceleration due to gravity –directed to center of Earth Think: scalar or vector? Why?

15 Generalized Motion Motion can be viewed as a combination of movements –vertical component typically gravitational acceleration –horizontal component some force from muscle, gunpowder, etc.

16 Question for Thought Do you recall what inertia is?

17 Question for Thought Where does the unit s 2 (or concept of “square second”) come from?

18 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

19 Newton’s Laws of Motion Newton’s Third Law of Motion –for every force there is an equal and opposite force (action and reaction)

20 Question for Thought How can there ever be an unbalanced force on an object if every action has an equal and opposite reaction?

21 Momentum By definition momentum is the product of – mass and velocity Conservation of momentum –total momentum of a closed system remains constant

22 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

23 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) / r 2