PHYS1171 Lecture 2 - Newton's Laws

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

PHYS1171 - Forces and MotionLecture 2 - Newton’s Laws

A/Prof Tim McIntyre

The University of Queensland

Semester 1, 2014

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Contact Details

A/Prof Tim McIntyre

3365 3423

[email protected]

By appointment

Room 325Building 6Physics Annex

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Study Expectations

Consult Blackboard forclass details

Do the pre-reading(5 Min Phys)

Attend class

Attempt tutorial andsupplementary questions(textbook)

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Where to get help

Me Friends

Tutor

FacebookPHYS1171Sem 1, 2014

Physics Learning Centre (PLC)12.30-1.30 pmWeekdays (from Week 2)

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Exam Questions (for my part)

Concepts - “Explain how

the body transfers heat

to the surrounds...”

Problem solving -“Calculate the speed of

blood through a

constricted artery

given...”

Not a memory test -formula sheet provided!

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Using your Keepad Clicker

Setting the channel:

Press & release GO button

Light flashes red & green, enter channel number (41)

Press & release the GO button

Light should turn green to confirm

When answering a question:

Click a number (from those available!)

Can change your selection (i.e. click a di↵erent number)

Green flash - answer received

Orange flash - no question available or no receiver

Red flash - failed, probably wrong channel

No flash - battery dead. See the library ASAP

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Using your Keepad Clicker

Clicker registration:

Assessable ‘Reading Quiz’ questions

Regular non-assessable quiz questions

Clicker identified by 6 digit hex code - e.g. 0D8AEF (onback)

Enter this number only through the Clicker Blackboardquiz by end Week 3.

Progress scores will be posted on Blackboard

To change your clicker, e-mail Tim McIntyre([email protected]) with the new clicker number andyour full student number - don’t overwrite the old number

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Technology Test

My primary degree is

1 Science

2 Biomedical Sciences

3 Human Movement Studies

4 Biotechnology

5 Food Technology

6 Engineering

7 Arts

8 IT

9 Other

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Technology Test

I’m enrolled in this course because (please select the mostappropriate)

1 I’m interested in Physics and would like to learn more

2 I think it will be useful for my degree

3 I’m trying to improve my GPA

4 I’m taking this course to help me get into medicine

5 I didn’t take Physics at High School and need this coursebefore continuing in Engineering

6 It’s a compulsory course for my degree

7 Some other reason

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Technology Test

I studied Physics in High School

1 Yes

2 No

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Technology Test

I’ve taken (or am taking) SCIE1000

1 Yes

2 No - but I am enrolled in the BSc

3 No - I‘m not enrolled in the BSc

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Motion - Types

Motion with constant acceleration (or force)

Circular motion withacceleration/force towards a centralpoint

Simple harmonic motion (restoring force)

Other motion under a changing force

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Lecture 2 - Newton’s Laws

Today’s lecture covers

What is a force?

Newton’s Laws

Free-body diagrams

Preparation

Read Five Minute Physics -Lecture 2 - Introduction to Forces

Reference

Biological Physics (2010), Section 2.1, 2.2

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Force

What is a force?

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Force

The forces on the object are . . .

Voyager 1 (artist’s rendition).

Image courtesy

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Force


Space Shuttle Discovery in orbit.

Image courtesy NASA

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Force


Apollo Command Module re-entering the atmosphere

(artist’s rendition)

Image courtesy NASA

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Force


Tim sliding

Image courtesy of Tim

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Force


Tim’s forearm

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Force

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Reading Quiz (assessed)

In describing motion, which of the following statements isfalse?

1 The unit of force is N (= newton)

2 Gravity is one of the four fundamental forces

3 An object in motion will slow down unlessacted on by an external force

4 Newton’s Second Law says acceleration isforce divided by mass

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Newton’s Laws

Set of laws that define force . . .

http://www-gap.dcs.st-and.ac.uk/history/PictDisplay/Newton.html

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Question...

The earth and the moon attract each other due to gravitationalforces. How do the magnitude of these forces compare?

1 The earth exerts a bigger forceon the moon

2 The moon exerts a bigger forceon the earth

3 The forces are equal

4 The forces are zero because theycancel out

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Force

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Newton’s Third Law

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Reading Quiz (assessed)

Dynamic equilibrium of a body means

1 The body is falling only under the influence ofgravity

2 The body is moving but has no net forceacting on it

3 The body is balanced but rocking back andforth

4 The body satisfies the requirements ofNewton’s Third Law.

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Question...

A book is lying on a table. The book will remain there at restbecause

1 There is a net force but the book is too heavyto move

2 There are no forces acting on it at all

3 It does move, but too slowly to be seen

4 There is no net force on the book

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Question...

A penguin slides on ice at a constant velocity. Which of thefollowing is true about the net force acting on the penguin?

1 The net force depends on the penguin‘s weight

2 The net force is zero

3 The net force depends on the penguin‘s speed

4 The net force depends on how rough the ice is

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Newton’s First Law

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Question...

A force, F

1

is applied to a car with mass m

1

causing it toaccelerate at a rate a

1

. If I applied double the force to a car ofhalf the mass the acceleration a

2

would be

1 a

1

/4

2 a

1

/2

3 a

1

4 2a

1

5 4a

1

PHYS1171 Lecture 2

Lecture 2

PHYS1171

Overview

Introduction

Force

Newton

Summary

Summing Up

After this lecture you should . . .

Be able to identify and explain forces on an object

Understand and apply Newton‘s Laws

Be capable of drawing free-body diagrams

Supplementary Questions Biological Physics (2010)

Problems 2.1, 2.7, 2.8

Next lecture

Read Five Minute Physics -Lecture 3 - Resolving Forces

Exam tip . . .

PHYS1171 Lecture 2

0%#

5%#

10%#

15%#

20%#

25%#

30%#

35%#

40%#

45%#

1#Science# 2#Biomedical#Sciences#

3#Human#Movement#Studies#

4#Biotechnology# 5#Food#Technology#

6#Engineering# 7#Arts# 8#IT# 9#Other#

My#primary#degree#is!!

0%#

5%#

10%#

15%#

20%#

25%#

30%#

35%#

40%#

45%#

1#I‘m#interested#in#Physics#and#would#like#

to#learn#more#

2#I#think#it#will#be#useful#for#my#degree#

3#I‘m#trying#to#improve#my#GPA#

4#I‘m#taking#this#course#to#help#me#get#into#

medicine#

5#I#didn’t#take#Physics#at#High#School#and#

need#this#course#before#conQnuing#in#Engineering#

6#It‘s#a#compulsory#course#for#my#degree#

7#Some#other#reason#

I‘m#enrolled#in#this#course#because#(please#select#the#most#appropriate)#!!

0%#

10%#

20%#

30%#

40%#

50%#

60%#

70%#

80%#

1#Yes## 2#No#

I#studied#Physics#in#High#School#!!

0%#

5%#

10%#

15%#

20%#

25%#

30%#

35%#

40%#

45%#

50%#

1#Yes# 2#No#V#but#I#am#enrolled#in#the#BSc## 3#No#V#I‘m#not#enrolled#in#the#BSc#

I‘ve#taken#(or#am#taking)#SCIE1000#!!

0%#

10%#

20%#

30%#

40%#

50%#

60%#

70%#

80%#

90%#

1#The#unit#of#force#is#N#(=#newton)# 2#Gravity#is#one#of#the#four#fundamental#forces#

3#An#object#in#moQon#will#slow#down#unless#acted#on#by#an#external#force#

4#Newton’s#Second#Law#says#acceleraQon#is#force#divided#by#mass#

Which#of#the#following#statements#is#false?#!!

√

0%#

10%#

20%#

30%#

40%#

50%#

60%#

1#The#earth#exerts#a#bigger#force#on#the#moon#

2#The#moon#exerts#a#bigger#force#on#the#earth#

3#The#forces#are#equal# 4#The#forces#are#zero#because#they#cancel#out#

The#earth#and#the#moon#a`ract#each#other#due#to#gravitaQonal#forces.#How#do#the#magnitude#of#these#forces#compare?!

0%#

10%#

20%#

30%#

40%#

50%#

60%#

70%#

80%#

90%#

1#The#earth#exerts#a#bigger#force#on#the#moon#

2#The#moon#exerts#a#bigger#force#on#the#earth#

3#The#forces#are#equal# 4#The#forces#are#zero#because#they#cancel#out#

The#earth#and#the#moon#a`ract#each#other#due#to#gravitaQonal#forces.#How#do#the#magnitude#of#these#forces#compare?#(repeat)!

√

0%#

10%#

20%#

30%#

40%#

50%#

60%#

70%#

80%#

1#The#body#is#falling#only#under#the#influence#of#gravity#

2#The#body#is#moving#but#has#no#net#force#acQng#on#it#

3#The#body#is#balanced#but#rocking#back#and#forth#

4#The#body#saQsfies#the#requirements#of#Newton’s#Third#Law.#

Dynamic#equilibrium#of#a#body#means##!

√

0%#

10%#

20%#

30%#

40%#

50%#

60%#

70%#

80%#

90%#

1#There#is#a#net#force#but#the#book#is#too#heavy#to#move#

2#There#are#no#forces#acQng#on#it#at#all# 3#It#does#move,#but#too#slowly#to#be#seen# 4#There#is#no#net#force#on#the#book#

A!book!is!lying!on!a!table.!The!book!will!remain!there!at!rest!because!

√

0%#

10%#

20%#

30%#

40%#

50%#

60%#

70%#

1#The#net#force#depends#on#the#penguin‘s#weight#

2#The#net#force#is#zero# 3#The#net#force#depends#on#the#penguin‘s#speed#

4#The#net#force#depends#on#how#rough#the#ice#is#

A#penguin#slides#on#ice#at#a#constant#velocity.#Which#of#the#following#is#true#about#the#net#force#acQng#on#the#penguin?!!

√

0%#

5%#

10%#

15%#

20%#

25%#

30%#

35%#

40%#

45%#

1#a1/4## 2#a1/2## 3#a1# 4#2a1## 5#4a1#

A#force,#F1#is#applied#to#a#car#with#mass#m1#causing#it#to#accelerate#at#a#rate#a1.#If#I#applied#double#the#force#to#a#car#of#half#the#mass#the#acceleraQon#a2#

would#be!!

√

PHYS1171, Semester 1, 2014 Forces and Motion

Lecture 2

Answers to recommended textbook questions 2.1 (a) 49 N; (b) 49.6 N; (c) 49 N; (d) 48 N 2.7 (a) 0.018 N (upwards); (b) 1.98 N (upwards); (c) Same as (b) but downwards 2.8 (a) 420 N; (b) 9.5 times larger

PHYS1171 Lecture 2 - Newton's Laws

Documents

Transcript of PHYS1171 Lecture 2 - Newton's Laws