Transcript Introduction to Modern Physics PHYX 2710

Physics of Technology
PHYS 1800
Lecture 10
Introduction
Review for Test 1
Section 0
Lecture 1
Slide 1
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 1
PHYSICS OF TECHNOLOGY
Spring 2009 Assignment Sheet
Date
Day
Lecture
Chapter
Jan 5
M
Class Admin: Intro.Physics Phenomena
1
6
T
Problem solving and math
App. B, C
7
W
Units, Scalars, Vectors,
1
9
F*
Speed and Velocity
2
Jan 12
M
Acceleration
2
14
W
Free Falling Objects
3
16
F*
Projectile Motion
3
Jan 19
M
Martin Luther King
No Class
21
W
Newton’s Laws
4
23
F*
Mass and Weight
4
Jan 26
M
Motion with Friction
4
28
W
Review
1-4
1-4
29
Th
Test 1
30
F
Circular Motion
5
Feb 2
M
Planetary Motion and Gravity
5
4
W
Energy
6
6
F*
Harmonic Motion
6
Feb 9
M
Momentum
7
11
W
Impulse and Collisions
7
13Introduction
F*
Rotational
8
Section
0 Motion
Lecture 1 Slide 2
Feb 16
M
Presidents Day
No Class
17
Tu
Angular Momentum (Virtual Monday)
8
18
W
Review
5-8
19
5-8
H
Test 2
INTRODUCTION TO Modern Physics PHYX 2710
20
F*
Static Fluids, Pressure
9
Fall 2004
Feb 23
M
Flotation
9
25
W
Fluids in Motion
9
27
F*
Temperature and Heat
10
Mar 2
M
First Law of Thermodynamics
10
Physics of Technology—PHYS 1800
4
W Spring 2009Heat flow and Greenhouse Effect Review 10
*Homework
Handout
6
F*
Climate Change
-
Homework Due
-
1
2
3
4
5
-
6
Lecture 10 Slide 2
7
Physics of Technology
PHYS 1800
Lecture 8
Mass & Weight
Motion with Friction
Introduction
Section 0
Lecture 1
Slide 3
Introduction and Review
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 3
Notes on Test
1. Covers Chapters 1-4
2. ~8 short answer problems or questions (5 point
each)
3. 3 Numerical problems based heavily on the
material from the homework and Lab/Demo
sessions (20 points each). One problem each from
Chapters 2, 3 and 4.
4. You will have a formula sheet just like the one in
Introduction
Section 0 Lecture 1 Slide 4
the handout.
5. Test is Thursday January 29 1:30-2:45 in ESLC 46.
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 4
What Do We Need To Measure?
• What is the minimum about things we need to know?
• Where things are—a length, L
• When things are there—a time, T
• How thing interact with gravity—a mass, M
• How things interact with E&M—a charge, Q
Introduction
Section 0
Lecture 1
Slide 5
• How thing inter act with weak nuclear force
• How things interact with strong nuclear force
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 5
Scalars and Vectors
• Scalar: Measure of quantity or size
•
Sometimes called “magnitude”.
•
Examples: Length, volume, mass, temperature,
speed…
• Vectors: Many measurements in physics require a
knowledge of the magnitude and direction of quantity.
•
These are termed vector quantities.
•
Examples: Velocity, acceleration, force, electric field…
• Direction
is an essential feature of a vector quantity.
Introduction Section 0 Lecture 1 Slide 6
•
Example: Flying at 1000 km/hr due North is quite
different to the same speed due East!
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
• Vectors require 2 pieces of information MAGNITUDE and
DIRECTION.
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 6
Describing (Special) Motion
Position—where you are in space (L-meter)
Speed—how fast position is changing with time (LT-1
or m/s)
Acceleration—how fast speed is changing with time
(LT-2 or m/s2)
1 Slide 7
We willIntroduction
focusSection
on0 aLecture
special
case of constant
acceleration due to gravity, termed FREE FALL.
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 7
Acceleration 
Speed 
Distance 
Constant Acceleration
Time
Time
Introduction
Section 0
Lecture 1
Time
Slide 8
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 8
The Math Approach
• Let’s put these ideas into math language
ag
v f  v0  at or a 
v f  vo
t
 v f  vo   v f  vo   vo vo 
t  
t    t
d  vavg t  
 2   2  2 2
 v1f Slidev9o 
vo 0 Lecture
1 2
 vo Section
Introduction
d 
t    t  v0t  at
2
 2   2 2
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 9
• Let the initial velocity be 20
m/s upward.
– It immediately starts
experiencing a downward
acceleration due to gravity, of
approximately 10 m/s.
– Every second, the velocity
decreases by 10 m/s.
• After 2 s, the ball has reached
its highest point.
– Its velocity changes direction,
from upward to downward,
passing through a value of 0
m/s. Introduction Section 0 Lecture 1 Slide 10
• Now, the downward
acceleration increases the
downward velocity.
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 10
Which of these three balls would hit the floor first if
all three left the tabletop at the same time?
a)
b)
c)
d)
The ball with initial
velocity v1.
The ball with initial
velocity v2.
The ball with initial
velocity v3.
They would all hit at the
same time.
Since all three balls undergo the
same downward
acceleration, and
Introduction Section 0 Lecture 1
they all start with a vertical
velocity of zero, they would all
fall the same distance in the
same time!
Slide 11
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 11
Projectile Motion
• Treating the vertical motion independently of the
horizontal motion, and then combining them to find
the trajectory, is the secret.
– A horizontal glide combines with a vertical plunge to
produce a graceful curve.
– The downward gravitational acceleration behaves the
same as for any falling object.
– There is no acceleration in the horizontal direction if air
resistance can be ignored.
– The projectile moves with constant horizontal velocity
while it is accelerating downward.
Introduction
Section 0
Lecture 1
Slide 12
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 12
Dennison’s Laws of Motion
1. Stuff happens (or not).
2. The bigger they are the harder
they fall.
3. You get what you give.
Introduction
Section 0
Lecture 1
Slide 13
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 13
Newton’s Laws in Review
•
1st Law —a special case of the 2nd Law for statics,
with a=0 or Fnet=0
• An objects velocity remains unchanged, unless
a force acts on the object.
•
2nd Law (and 1st Law)—How motion of a object is
effected by a force.
– The acceleration of an object is directly
proportional to the magnitude of the imposed
force and inversely proportional to the mass of
the object. The acceleration is the same
direction as that of the imposed force.
F  ma
units: 1 newton = 1 N = 1 kg m s2
•
Introduction
Section 0 Lecture 1
3rd Law —Forces come
Slide 14
from interactions with
other objects.
• 
For every action (force), there is an equal but
opposite reaction (force).
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 14
Newton’s First Law of Motion
An object
remains at rest,
or in uniform
motion in a
straight line,
unless it is
compelled to
change by an
externally
imposedIntroduction
force. Section 0
Lecture 1
Slide 15
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 15
Newton’s Second Law of Motion
 Note that a force is proportional to an object’s
acceleration, not its velocity.
 Precise definitions of some commonly used terms:
 The mass of an object is a quantity that tells us how much
resistance the object has to a change in its motion.
 This resistance to a change in motion is called inertia.
F  ma
Introduction
Section 0
Lecture 1
Slide 16
units: 1 newton = 1 N = 1 kg m s2
Force has dimensions of (MLT-2)
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 16
Fstring  10 N (t o the right)
Net Forces
 It is the total force or net force
that determines an object’s
acceleration.
 If there is more than one vector
acting on an object, the forces are
added together as vectors, taking
into account their directions.
ftable  2 N (t o the left )
Fnet  10 N  2 N
 8 N (t o the right)
a
Fnet 8 N

m 5 kg
 1.6 m s2 (t o t he right
Introduction
Section 0
Lecture 1
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Slide 17

Review
Lecture 10 Slide 17
Newton’s Third Law (“action/reaction”)
For every action (force),
there is an equal but
opposite reaction
(force).
Introduction
Section 0
Lecture 1
Slide 18
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 18
Mass, Weight, and Inertia
• A much larger force is
required to produce the
same acceleration for the
larger mass.
• Inertia is an object’s
resistance to a change in
its motion.
• Mass is a measure of
an object’s inertia.
Introduction
Section 0
Lecture 1
Slide 19
• The units of mass are
kilograms (kg).
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 19
Does a sky diver continue to accelerate?
Air resistance R is a force
directed upward, that
opposes the gravitational
force W
R increases as the sky
diver’s velocity increases
When R has increased to
the magnitude of W, the net
force is zero so the
acceleration is zero
Introduction Section 0 Lecture 1 Slide 20
The velocity is then at its
maximum value, the
terminal velocity
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 20
Free Body Diagrams
• Fancy Science: Vector analysis of complex force
problems is facilitated by use of a free body
diagram.
• Common Sense: A picture is worth a 100 words.
(A scale picture is worth an A!)
• Key is to:
• Isolate a single body and draw all the forces acting on it.
• Add up all the arrows (vectors).
Introduction Section 0 Lecture 1 Slide 21
• What’s left is the net force.
• Net force (and masses)  a.
• A plus initial conditions motion!
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 21
Example: Sea Lion splash!
Fk
N
Fk
N
F|| =mg sinθ
θ
mg cosθ
F||
θ
Free body
diagram
θ
W=mg
W=mg
Resolve the weight force into two components –
parallel and perpendicular to ramp.
Result: - Down slope force F|| = m g sin θ
- Normal force
N = m g cos θ
Introduction
Section 0
Lecture 1
Slide 22
INTRODUCTION TO Modern Physics PHYX 2710
Fall 2004
Physics of Technology—PHYS 1800
Spring 2009
Review
Lecture 10 Slide 22