lec21-particle physics intro

7/27/2019 Lec21-Particle Physics Intro

1/23

Announcements

Pick up A,B,C,D cards. Please bring them to class with you.

Bring a calculator to lab. In many cases, you will need it.

Course book A Tour of the Subatomic Zoo is available at

Bookstore until April 15. So, please purchase it asap.

In most cases, I will be making the lecture notes available on themorning of lecture. I encourage you to make a copy and bringthem to class. Note that there are things I cover in class which arenot on the slides. You are responsible for both, soplease dontmiss class.

Yes, there is LAB this week.


2/23

Welcome to Particle Physics

Were barely aware that they are there, but the elementary particles of matterexplain much of what we take for granted every day. Because ofgluons

binding the atomic nucleus, matter is stable and doesnt crumble. Because ofgravitons, our feet stay firmly planted on the ground. We see because oureyes react tophotonsof light.

Particle Physics explains the ordinary, and delights us with tales of theextraordinary. Antimatter annihilates matter. Virtual particles blink in andout of existence in the vacuum of space. Neutrinos zip through the Earth

untouched.

Particle Physics doesnt stop at the unusual either. It contemplates thecosmic too, exploring the origins of the universe and the symmetries thatframe its design.

A blurb from the Quarks Unbound from the

American Physical Society


3/23

Aims of Particle Physics

1. To understand nature at its most fundamental level.

2. What are the smallest pieces of matter, and how do

they make up the large scale structures that we see

today ?

3. How and why do these fundamental particlesinteract the way that they do?

4. Understand the fundamental forces in nature.


4/23

In this course, my aim is to

introduce you to nature at its

most fundamental level

Some of the concepts you will encounter may not agree with

your intuition, others will

I strongly encourage you to ask questions in class.

It will help you, your classmates, and me!

Before we can get to this, we will first spend some time on

some basics, and then well get to the meat later on.


5/23

Sizes and Powers of 10

In describing nature, objects vary dramatically in size.

The solar system is about 10,000,000,000,000,000,000,000 times

larger than an atom, for example Scientific notation !

You should become comfortable with seeing scientific notation,in the context of relative sizes of objects.

Useful Web Sites which allow you to step through the powers of

10 are at:

http://cern.web.cern.ch/CERN/Microcosm/P10/english/P0.htmlhttp://www.wordwizz.com/pwrsof10.htm

http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/
http://cern.web.cern.ch/CERN/Microcosm/P10/english/P0.htmlhttp://www.wordwizz.com/pwrsof10.htmhttp://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/http://www.wordwizz.com/pwrsof10.htmhttp://cern.web.cern.ch/CERN/Microcosm/P10/english/P0.html


6/23

Powers of 10

1

1

1 10.1 10

10 10

2

2

1 1 1 10.01 10

100 10 10 10

x

3

3

1 1 1 1 10.001 10

1000 10 10 10 10x x

1 1 1 31000 10 10 10 10 10 10 10x x x x

1 1 2100 10 10 10 10 10x x

1

10 10

Positive

Powers

Negative

Powers

100 = 10 Power


7/23

Scientific Notation

12500 = 1.25 x10000 = 1.25 x(10 x10 x10 x10) = 1.25 x 104

1.2500 Move decimal 4 places to right1.25x10? 12500.0

0.00367 = 3.67 x 0.001 = 3.67 x(.1 x .1 x.1) = 3.67 x 10-3

3.673.67x10? 0.00367 Move decimal 3 places to left

The sun has a radius of 695 million meters. How is this expressed

in scientific notation?

A) 695x105 B) 6.95x108 C) 6.95x109 D) 6.95x106

The earth has a circumference of about 25,000 miles. How is this

expressed in scientific notation?

A) 2.5x103 B) 25x104 C) 2.5x104 D) None of these


8/23

Multiplying powers of 10

The circumference of the earth is about 4x107 [m]. If I were to

travel around the earth 3x102 times, how many [m] will I have gone?

A) 7.0x109 B) 1.2x1010 C) 1.0x1015 D) 7.0x1015

(4x107)x (3x102) = (4x3)x (107x102) = 12x10(7+2) = 12x109

= (1.2x10)x109

= 1.2x1010

A bullet takes 10-3 seconds to go 1 [m]. How many seconds will it

take for it to go 30 [m]?A) 3.0x10-1 B) 3.0x10-2 C) 4.0x10-2 D) 4.0x10-1

(1x10-3)x (3x101) = (1x3)x (10-3x101) = 3x10(-3+1) = 3x10-2


9/23

Dividing Powers of 10A gas truck contains 4.6x103 gallons of fuel which is to be distributed

equally among 2.0x104

cars. How many gallons of fuel does each carget?

A) 2.3x101 B) 2.3x10-1 C) 23 D) 2.3

3 3

(3 4) 14 4

4.6 10 4.6 10* 2.3 10 2.3 102.0 10 2.0 10

x

x x

x

The area of the U.S is about 3.6x106 [miles], and the population is

about 300x106. On average, what is the population density in persons

per square mile?A) 1.2x102 B) 1.2x10-1 C)1.2x10-3 D)1.2x10-2

6 6(6 8) 2

8 8

3.6 10 3.6 10* 1.2 10 1.2 10

3.0 10 3.0 10

x

x x

x


10/23

Common Prefixes

Commonly used prefixes

indicating powers of 10

10

3

= kilo106= mega

109= giga

1012= tera

10-3= milli

10-6= micro

10-9= nano

10-12= pico

10-15= femto

1 km = 103 m and there are 106 micrometers in a meter, sothere are 109 (or 1 billion) micrometers in 1 km

How many times larger is a kilometer than a micrometer ?

A) 1,000 B) 1,000,000 C) 1,000,000,000 D) 1x10-9

How many 100 W bulbs can be kept lit with 100 Tera-Watts?

A) 1.0x107 B) 1.0x109 C) 1.0x1012 D)1.0x1013


11/23

Common Conversions

Length: 2.54 [cm] = 1 [inch]Mass: 1 [kg] = 2.2 [lbs]

Speed: 1 [m/sec] = 2.25 [mi/hr]

How many meters are there in a centimeter?

A) 100 B) 0.01 C) 1000 D) 0.001

How many inches in 1 kg ?

A) 2.54 B) 25.4 C) less than 25 D) None of these


12/23

Units

Joe asks Rob About how much does your car weigh ?

Joe answers About 1.5

Is Joes answer correct or incorrect?

Physical quantities have units !!!!!!!!

All physical quantities have units, and they must be used.

One exception is if you are talking only about a pure number.

For example: How many seats are in this classroom?

I will often use bracketsto indicate units:

1 kilogram == 1 [kg]


13/23

Variables/Symbols

It is often more convenient to represent a number using a letter.

For example, the speed of light is 3x108 [m/sec]. To avoid having to

write this every time, we simply use the letterc which represents

this value. That is c = 3x108 [m/sec].

We might use the expression, the particle is moving at 0.1c.

This should be interpreted as

The particle is moving at 1/10thof the speed of light.

We will often use letters to represent constants or variables, so

you must become comfortable with this.


14/23

Proportionality

What do we mean when we say:

Quantity A is proportional to quantity B

This means the following:

1) If we double B, then A also doubles.

2) If we triple B, then A also triples.

3) If we halve B, then A also halves.

This is often written as: AaB

The circumference of a circle, C, is proportional to the radius, R.

If the radius is increased by a factor of 10, what happens to the

circumference?

It increases by a factor of 10


15/23

Proportionality Exercises

Consider this 1 cm squarel

What is its area?

Area = base * height = l*l= l2 = (1 cm )2 = 1 cm2

Whats the area of this square? 2l

Area = base * height = 2l*2l= 4l2 = 4(1 cm )2 = 4 cm2

l

l

If we double the length of the side,

we quadruple the area?


16/23

Proportionality Exercises (cont)

The area of a circle is proportional to the radius squared.

What happens to the area of a circle if the radius is doubled?

Radius = 2 cm Radius = 4 cm

A=pr2

Since A a r2, (A=pr2)

doubling the radius quadruples the area !

A=p(22) = 4p A=p(42) = 16p


17/23

Inverse Proportionality

What do we mean when we say a quantity V is

inversely proportionalto another quantity, say d.

V a (1/d)It means:

If we double d, then V is reduced by a factor of2

If we quadrupled, then V is reduced by a factor of4.

Why?

We know that Vd a (1/d)If we double d, then d (2*d), so

V2d a [1/(2d)] = (1/2) (1/d) = (1/2) Vd.

In the same way, show that V4d = (1/4) Vd

i


18/23

ExercisesThe force of gravity is known to be inversely proportionalto

the square of the separationbetween two objects. What happens to the

force between two objects when the distance is tripled?

A) Increases by a factor of 6

B) Decreases by a a factor of 8

C) Decreases by a factor of 9

D) Decreases by a factor of 6

The electric force between two charges is also known to be inversely

proportional to the square of the separation. What happens to the force

if the distance is reduced by a factor of 10.

A) Increases by a factor of 10

B) Increases by a a factor of 100

C) Decreases by a factor of 10

D) Decreases by a factor of 100


19/23

Algebra

If a car is going 20 [mi/hr] for 4 [hrs], how far does the car go?

A) 80 [mi] B) 5 [mi] C) 20 [mi] D) none of these

What did you do to arrive at this result?

You multiplied the speed (20 [mi/hr]) by the time (4 [hrs]).

So, to get the distance, you did this:

distance = velocity * time

d = v*t


20/23

Algebra (cont)

If a biker goes 20 [mi] in 2 [hrs], what is the bikers average speed ?

A) 20 [mi/hr] B) 5 [mi/hr] C) 10 [mi/hr] D) 40 [mi/hr]

What did you do to arrive at this result?

You divided the distance (20 [mi]) by the time (2 [hrs]).

That is, you reasoned:

average velocity = distance / time

v = d / t

Is this equation and the previous one expressing

different relationships among the variables v, d and t?


21/23

Algebra (cont)

NO!

d = v * t v = d / tand Are expressing thesame relationship. The

variables are just

shuffled around a bit!

To cast the first form into the second:

d = v * t

Multiply both sides by (1/t):

The factor oft * (1/t) = 1, so

And, (1/t)*d = d/t,

Or, just switching sides

(1/t)* *(1/t)d = v * td = v(1/t)*

d / t = v

v = d / t


22/23

An important example

E = m c2

Einsteins famous Energy-mass relation:

Can be rearranged to read:

m = E / c2

Note that the units of mass can also be expressed in units of

Energy / (speed)2

(Well come back to this point later)


23/23

Summary

For this module, you should be comfortable with:

1. Using and manipulating powers of 10 (division, multiplication).

2. Understanding what proportional to and inversely

proportional to mean.

3. Simple conversion of units, if you are given the conversion

factors. (e.g. [in.] to [cm], [cm] to [m]., etc)

4. Basic algebra and manipulating equations such as, E=mc2,

c=fl , E=hf , etc.

5. Understanding prefixes, such as Giga, Tera, Mega, etc.

lec21-particle physics intro

Documents