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HONORS 2271 September 2015

Dr. Harold GellerCollege of Science

School of Physics, Astronomy and Computational Sciences

George Mason University

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Chapters 1 and 2 andOther Stuff

•A Personal Response System (iClickers)

•Units of length, mass and time•Metric Prefixes•Chapter 2 and the Ordered

Universe

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

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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”

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

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Common Prefixes for Powers of Ten

Factor Name Symbol

(billion) 109 Giga- G

(million) 106 Mega- M

(thousand) 103 kilo- k

(hundredth) 10-

2 centi- c

(thousandth) 10-

3 milli- m

(millionth) 10-

6 micro-

(billionth) 10-

9 nano- n

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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

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Science is an adventure of the human mind

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HNRS 227Chapter 2 – Ordered Universe

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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

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Speed and Velocity

• Speed– distance traveled in a unit of time– a scalar quantity

• Velocity– speed and direction– a vector quantity

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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

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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

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Acceleration Due to Gravity

• Direction of acceleration due to gravity– directed to center of Earth

• Think: scalar or vector?

• Why?

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Generalized Motion

• Motion can be viewed as a combination of movements– vertical component

• typically gravitational acceleration

– horizontal component• some force from muscle, gunpowder, etc.

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Question for Thought

• Do you recall what inertia is?

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Question for Thought

• Where does the unit s2 (or concept of “square second”) come from?

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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

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Newton’s Laws of Motion

• Newton’s Third Law of Motion– for every force there is an equal and

opposite force (action and reaction)

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Question for Thought

• How can there ever be an unbalanced force on an object if every action has an equal and opposite reaction?

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Momentum

• By definition momentum is the product of

– mass and velocity

•Conservation of momentum–total momentum of a closed system remains constant

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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

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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