PHY205 Physics of Everyday Life · PDF file · 2013-04-10• Starting Chapters 2 and 3 of Conceptual Physics (we are skipping chapter 1..) • Motion, ... • To begin class at 10

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PHY205H1F Summer

Physics of Everyday Life

Class 1

• Welcome - please make yourself

comfortable!

• I am Jason Harlow, the instructor for

this course

• Today I will introduce the course,

and start in on the first 2 chapters:

• Chapters 2 and 3 from

• Conceptual Physics by P.G.Hewitt

Today’s Outline

• Introduction Who am I? What is physics?

• Run of the Course Clickers, Pre-Class

Quizzes, Tutorials, Problem Sets, Test and

Exam

• Starting Chapters 2 and 3 of Conceptual

Physics (we are skipping chapter 1..)

• Motion, Force, Inertia

• Newton’s First Law

• Relative Motion

• Speed, Velocity, Acceleration

• Free Fall

Who am I?

• Jason Harlow, Senior Lecturer

• B.Sc. in Physics at U of Toronto 1993

• Ph.D. in Astronomy and Astrophysics at

Penn State 2000

• I have been teaching at U of T for 8 years

• Contact Info: [email protected]

• 416-946-4071 Office: MP121B

• Office hours: Mondays and Wednesdays: 10-11AM,

Fridays: 9-10AM. In addition to these hours, you

have are invited to call or email for an appointment,

or just drop by my office.

Other Important Contacts

• Ms. April Seeley, Course Administrative

Assistant

• [email protected]

• 416-946-0531

• Office: MP129

• Office hours: Monday,Tuesday, Thursday, Friday

9:30am to 5:00pm, and Wednesdays from 9:30am

to 4:30pm

• Your T.A. – you will meet May 13 or 15

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What is Physics? • Paul Hewitt, the author of the course textbook,

says:

“You know you can’t enjoy a game unless you know its

rules; whether it’s a ball game, a computer game, or

simply a party game. Likewise, you can’t fully appreciate

your surroundings until you understand the rules of

nature.

Physics is the study of these rules, which show how

everything in nature is beautifully connected. So the

main reason to study physics is to enhance the way you

see the physical world.

You’ll see the mathematical structure of physics in frequent

equations, but more than being recipes for computation,

you’ll see the equations as guides to thinking.”

Physics at U of T • Some of the top research fields in our department

are:

• Atmospheric – Observational and Computational

• Biological Physics

• Condensed Matter Physics – Theoretical and

Experimental

• High Energy Particle Physics – Theoretical and

Experimental

• Geophysics

• Quantum Optics

• Physics Education Research

Physics at U of T Physics at U of T • Angry Birds at Summer Science Camp (held in

August), led by Professor Sabine Stanley (Earth,

Atmospheric and Planetary Physics)

3

Show of hands

• What would you describe as your main

area of study at U of T?

– Humanities (Arts)

– Rotman Commerce

– Computer Science

– Social Sciences

– Other?

Who Should be Taking This

Course? • To do well in this course, you must be familiar with life

on earth, including moving, breathing and eating.

• It also helps if you have some experience thinking about

light, sound or music, and if you have ever used an

electric device, or played with magnets.

• There are no pre-requisites for this course but there are

exclusions!

• This course is primarily intended to be a breadth course

for students in the humanities, social sciences,

commerce, etc. You may not take this course if you

have ever taken or are taking PHY131, PHY151, or any

equivalent laboratory-based first year physics course.

My Goals for You • Begin to see physics in everyday life

• Learn that physics isn’t frightening

• Learn to think logically in order to solve physics

problems

• Develop and expand your physical intuition

• Learn how things work

• Begin to understand that the universe is

predictable rather than magical

• Obtain a perspective on the history of science

and technology

My Goals for Me

• To try to teach well and explain physics

clearly, at an appropriate level.

• To treat you with courtesy, respect and

kindness.

• To be fair.

• To be in my office at scheduled office

hours.

• To answer emails within 48 hours.

• To begin class at 10 after the hour and end

on the hour.

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What you need to buy (3 things) 1. The required textbook: "Conceptual Physics" 11th

edition, by Paul Hewitt ©2011 by Pearson Education.

There is a custom edition for U of T St. George at the

campus bookstore which includes only the chapters we

will be covering in this course: 2-5, 7 , 8, 13-16, and 19-

28. It also contains an i-clicker rebate coupon.

Custom cover:

Regular cover

What you need to buy (3 things) 2. An i-clicker personal remote. Available at the

campus bookstore New: $36, used: $27. You will be

registering this online with your UTORid for marks.

What you need to buy (3 things) 3. A calculator - this doesn’t need to be too fancy, but it

must have SIN, COS, TAN buttons on it. For example a

new Casio fx-260 is $16.

Pre-Class Reading Quizzes • In order to get the best out of my classes (which will

include lots of clicker questions and discussion) you must

read the chapters before coming to class

• If you hate reading, I have also posted 20 minute pre-class

videos, which go over the main points from each day’s

chapters

• Beginning this Wednesday, there will be a short online

multiple choice quiz due by 10:00am before class.

• You must access the quizzes on the portal site for this

course

• The quiz will be based on your reading or watching of the

pre-class video.

• The questions are not too tricky – if you’ve read the

material, you should find them quite straightforward.

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Tutorials • Tutorials begin this week.

• You should go to your tutorial once every

Monday or Wednesday

• See the web-site for your room location

based on your tutorial group on portal: “My

Tutorial Group”

• Tutorial worksheets are worth 5% of the

course mark.

• Problem Set 1 will be distributed in tutorial

this week and next Monday.

Tests

• The Midterm Test is Wednesday, May 29 from 1:10-3:00 in ??

• That is in just a little over 2 weeks from now!

• This test is worth 30% of the course mark.

• The tests will involve a combination of multiple choice and written questions, which will test your understanding of course material and ability to think and apply what you have learned to simple problems and explaining phenomena.

• A simple pocket calculator and a 5"×3" index card with your own hand-written notes will be permitted during the tests.

© 2010 Pearson Education, Inc.

Two balls are launched along a pair of tracks with

equal velocities, as shown. Both balls reach the

end of the track. Predict: Which ball will reach the

end of the track first?

• A

• B

• C: They will reach the end of the track at the

same time


Demo: Two balls were launched along a pair of

tracks with equal velocities. Both balls reached the

end of the track. Observe: Which ball reached the

end of the track first?

• A

• B

• C: They reached the end of the track at the

same time

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Why does ball reach the end of the track first? Explanation:

• Balls A and B start and end with the same

• But while ball B is on the lower part, it is going than ball A because gravity has sped it up.

• Its is greater, so it gets there

Chapter 2.

Galileo’s Inertia Experiment • A ball rolls down a hill, along a flat part,

and then up a hill again

• It tends to roll up to the same height from

which it was released (or a little less)

• What if there was no second hill?

• Q: What keeps an object going if it is

already moving?

• A:


• Born in 1643, the year died.

• Was a “physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian and one of the most influential people in human history.” (http://en.wikipedia.org/wiki/Isaac_Newton)

• In Philosophiæ Naturalis Principia Mathematica, published 1687, he described universal gravitation and the three laws of motion, laying the groundwork for classical mechanics.

Isaac Newton


What is a force? A force is a

A force acts on an

Pushes and pulls are applied to something

From the object’s perspective, it has a force on it

• The S.I. unit of force is

the

• 1 N = 1 kg m s–2

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7

Vector quantity

• a quantity whose description requires both

(how much) and (which way)

• can be represented by drawn to scale,

called

• length of arrow represents magnitude and arrowhead

shows direction

What is a force? Net Force Net force is the combination of all forces that

change an object’s state of motion.

Examples:

One person pushes a cart to the right with a

force of 5 N.

At the same time, a second person pushes the

same cart to the left with a force of 10 N.

What is the magnitude of the net force on the

cart?

A. 0 N

B. 5 N

C. 10 N

D. 15 N

Net Force


force of 5 N.



What is the direction of the net force on the

cart?

A. To the left

B. To the right

Net Force

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force of 5 N.



The net force on the cart is 5 N to the left.

Net Force

Two forces are in opposite

directions, so they

The direction is determined by the

direction of the

The Equilibrium Rule : Example

A string holding up a bag of flour

• Two forces act on the bag of flour:

– force acts upward.

– acts downward.

• Both are equal in magnitude and

opposite in direction.

– When added, they

– So, the bag of flour remains

Normal Force

The normal force on an object resting on a

flat surface is an upward force on an object

that is opposite to the force of gravity.

Example: A book on a table compresses

Atoms in the table, and the compressed

atoms produce the support force.

Understanding Normal Force

When you push down on

a spring, the spring

Similarly, when a book

pushes down on a table,

the table pushes

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Equilibrium of Moving Things

Equilibrium: a state of no change with no net

force acting

– Static equilibrium

Example: hockey puck at rest on slippery ice

– Dynamic equilibrium

Example: hockey puck sliding at constant speed on

slippery ice

Equilibrium of Moving Things A man pushes a crate with a force to the right.

The downward gravity force is balanced by an upward

normal force.

normal

gravity

push

Can this crate move at a constant velocity?

A. Yes

B. No, there must be another force involved.

Equilibrium of Moving Things

Equilibrium test: whether something

undergoes changes in motion Example: A crate at rest is in static equilibrium.

Example: When pushed at a steady speed, it is in

dynamic equilibrium.


Newton’s First Law

The natural state of an object with no net

external force on it is to either remain at rest

or continue to move in a straight line with a

constant velocity.

1

10


Thinking About Force

Forces exist due to interactions happening now,

not due to what happened in the past

Consider a flying arrow

A pushing force was

required to accelerate the

arrow as it was shot

However, no force is

needed to keep the arrow

moving forward as it flies

It continues to move because of

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The Reference Frame of a

Moving Car

Is it possible to juggle in a car that is moving at

100 km/h on the highway?

Yes!

Velocity is relative.

If your laboratory is enclosed inside the back of a

truck with no windows, there is no experiment

you can do to determine whether the truck is at

rest or moving along the highway at a steady

speed.

PHY205

Physics of Everyday Life

Chapter 3

• Motion Is Relative

• Speed : Average and Instantaneous

• Velocity

• Acceleration

• Free Fall

Joke: Why Did the Chicken Cross

the Road?

Aristotle (330 BC):

“Because

Newton (1687):

“Because

Einstein (1905):

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Motion Is Relative

Motion of objects is always described as

relative to something else. For example:

• On the subway you are

moving at 50 km/h North

relative to the platform.

• The person sitting

across from you is at

rest relative to you

• The station platform is

moving at

relative to you

Caught Speeding

• Officer: “Lady you were going 75 kilometres per

hour in a 50 zone.”

• Lady: “I’m sorry officer, but that can’t be.

• Officer: “No, no. What I mean is, if you had

continued driving at that speed for 1 hour, you

would go 75 kilometres.”

• Lady: “I’m sorry officer, but that’s not true. If I had

continued driving at that speed, I would surely have

• Officer: “Here’s your ticket, explain it to the judge!”

[Paraphrased from famous discussion in The Feynman Lectures on Physics, Vol. 1 by R.P. Feynman, R.B. Leighton

and M. Sands ©1964 by Addison-Wesley]

Speed

• Defined as the distance covered per

amount of travel time.

• Units are

• In equation form:

distanceSpeed =

time

Example: A girl runs 4 meters in 2 sec. Her speed is

Average Speed

• The entire distance covered divided by the total

travel time

– Doesn’t indicate various instantaneous speeds along

the way.

• In equation form:

total distance covered

Average speed time interval

Example: Drive a distance of 200 km in 2 h and your

average speed is

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Instantaneous Speed

Instantaneous speed is the speed at any

instant.

Example:

– When you ride in your car, you may speed up

and slow down.

– Your is given by your

speedometer.

Velocity

• A description of

– the of the object

– what the object is moving

• Velocity is a quantity. It has

– magnitude: instantaneous speed

– direction: direction of object’s motion

Speed and Velocity

• Constant is steady speed, neither

speeding up nor slowing down.

• Constant is

– constant speed and

– constant direction (straight-line path with no

acceleration).

Motion is relative to Earth, unless otherwise stated.

Acceleration

Formulated by Galileo based

on his experiments with

inclined planes.

Rate at which velocity

changes over time

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Acceleration

Because velocity is a vector, it can change in two possible ways:

1. The magnitude can change, indicating a change in speed, or

2. The direction can change, indicating that the object has changed direction.

Example: Car making a turn

Acceleration

In equation form:

Unit of acceleration is unit of velocity / unit of time.

Example:

• You car’s speed right now is 40 km/h.

• Your car’s speed 5 s later is 45 km/h.

• Your car’s change in speed is 45 – 40 = 5 km/h.

• Your car’s acceleration is 5 km/h/5 s = 1 km/h/s.

Three Equations of Constant Acceleration

(Good to put on your note-card)

This means the change in

speed is the acceleration

times the time elapsed. atvv if1.

2

i2

1attvd 2.

tvv

d

2

fi3.

This means the distance

traveled is related to the

initial speed times time plus

half the acceleration times

time squared.

This means the distance

traveled is the average speed

times time.

Example (Problem 3 from Chapter 3)

a. What is the instantaneous velocity of a freely falling

object 10 s after it is released from a position of rest?

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b. What is its average velocity during this 10 s interval?




b. What is its average velocity during this 10 s interval?

c. How far will it fall during this time?


Acceleration Direction for

Linear Motion

• When an object is speeding up, its velocity and acceleration are in the direction.

• When an object is slowing down, its velocity and acceleration are in directions.

• Direction can be specified with + or – signs.

• For example, something with positive velocity and negative acceleration is .

• Something with negative velocity and positive acceleration is also !

Acceleration Direction

• A car starts from rest, then drives to the right. It

speeds up to a maximum speed of 30 m/s. It coasts

at this speed for a while, then the driver hits the

brakes, and the car slows down to a stop.

• While it is speeding up, what is the direction of the

acceleration vector of the car?

A.to the right.

B.to the left.

C.zero.

v

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• While the car is coasting, what is the direction of the

acceleration vector of the car?

A.to the right.

B.to the left.

C.zero.

v


• While the car is slowing down, what is the direction

of the acceleration vector of the car?

A.to the right.

B.to the left.

C.zero.

v

Acceleration Galileo increased the inclination of inclined planes.

• Steeper inclines gave greater .

• When the incline was vertical, acceleration was

max, same as that of the falling object.

• When air resistance was negligible, all objects fell

with the same unchanging acceleration.

Free Fall

Falling under the influence of gravity only

- with no air resistance

• Freely falling objects on Earth accelerate at

the rate of 10 m/s/s, i.e., 10 m/s2

• This free fall acceleration depends on

and on the earth.

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• Average: 9.799 m/s2

• For Problem Sets, Tests and the Exam in this class: let’s use

g = 10 m/s2

Free Fall—How Fast?

The velocity acquired by an

object starting from rest is

So, under free fall, when acceleration is

10 m/s2, the speed is

• m/s after 1 s.

• m/s after 2 s.

• m/s after 3 s.

And so on.

Free Fall—How Far?

The distance covered by an accelerating

object starting from rest is

So, under free fall, when acceleration is 10 m/s2, the

distance is

• m after 1 s.

• m after 2 s.

• m after 3 s.

And so on.

Distance (1/2) x acceleration x time x time

Free Fall Acceleration Direction

• An angry bird starts with an upward

velocity, reaches a maximum height,

then falls back down again.

• While the bird is going up (after it has

left my hand), what is the direction of

the acceleration vector of the bird?

A.up.

B.down.

C.zero.

v

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• When the bird is momentarily stopped

at the top of its path, what is the

direction of the acceleration vector of

the bird?

A.up.

B.down.

C.zero.


• While the bird is going down (but

before I catch it), what is the direction

of the acceleration vector of the bird?

A.up.

B.down.

C.zero. v

Before Next Class • Buy a clicker! You will need it for the next

class!

• Please read Chapters 4 and 5, or at least

watch the pre-class video

• Note the first Pre-class reading quiz (on

chapters 4 and 5) is due Wednesday by

10:00am

• Note – Tutorials begin today or

Wednesday – go there for marks and to

pick up your first problem set

Documents

PHY205 Physics of Everyday Life · PDF file · 2013-04-10• Starting Chapters 2 and 3 of Conceptual Physics (we are skipping chapter 1..) • Motion, ... • To begin class at 10