Transcript Introduction to HONORS 227 & Science as a Way of Knowing

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