newton's first law of physics

8/17/2019 Newton's First Law of Physics

1/19

Chapter 2:

Newton's 1st

Law of

Chapter 2:

Newton's 1st

Law of


2/19

Figure 2.5


3/19


4/19

Aristotle’s Ideas of Motion

Aristotle’s classification of motion: Natural motion

− Every object in the universe has a proper placedetermined by a combination of four elements:earth, water , air , and fire.

− Any object not in its proper place will strive to getthere.

Eamples: !tones fall. "uffs of smo#e rise.

Aristotle’s classification of motion: Natural motion

− Every object in the universe has a proper placedetermined by a combination of four elements:earth, water , air , and fire.

− Any object not in its proper place will strive to getthere.

Eam

ples: !tones fall. "uffs of smo#e rise.


5/19

Aristotle’s Ideas of Motion

Natural motion (continued)

− Straight up or straight down for all things on Earth.

− $eyond Earth, motion is circular .

Eample: %he !un and &oon continually circle Earth.

Violent motion

− "roduced by eternal pushes or pulls on objects.Eample: 'ind imposes motion on ships.

Natural motion

(continued)

− Straight up or straight down for all things on Earth.

− $eyond Earth, motion is circular .

Eample: %he !un and &oon continually circle Earth.

Violent motion

− "roduced by eternal pushes or pulls on objects.Eample: 'ind imposes motion on ships.


6/19

Galileo’s Concept of Inertia

(alileo demolished Aristotle)s

assertions in the early *5++s.

Galileo’s discovery:

-bjects of different weight fall to the

ground at the same time in the

absence of air resistance. A moving object needs no force to

#eep it moving in the absence of

friction.

(alileo demolished Aristotle)s

assertions in the early *5++s.

Galileo’s discove

ry:

-bjects of different weight fall to the

ground at the same time in the

absence of air resistance. A moving object needs no force to

#eep it moving in the absence of

friction.


7/19

Force is a push or a pull.

&easured in units of Newtons N / 1 N = 1 kg∙m/s2

Inertia is a property of matter to resist changes in motion.

depends on the amount of matter in an object its

mass/.

Force is a push or a pull.

&easured in units of Newtons N / 1 N = 1 kg∙m/s2

Inertia is a property of matter to resist changes in motion.

depends on the amount of matter in an object its

mass/.



8/19


$alls rolling on downward0

sloping planes pic#ed up

speed.

$alls rolling on upward0sloping planes lost speed.

!o a ball on a hori1ontal plane

must maintain speed forever.

f the ball comes to rest, it is

not due to its 3nature), but due

to ICTION.

$alls rolling on downward0

sloping planes pic#ed up

speed.

$alls rolling on upward0sloping planes lost speed.

!o a ball on a hori1ontal plane

must maintain speed forever.

f the ball comes to rest, it is

not due to its 3nature), but due

toICTION

.


9/19

Figure 2.4


10/19

Newton’s First Law of Motion

“Every object continues in a state of

rest or of uniform speed in a straight

line unless acted on by a noneronet force!"

# translated from $atin from Ne%ton&s

Principia Mathematica Philosophiae

Naturalis

“Every object continues in a state of

rest or of uniform speed in a straight

line unless acted on by a noneronet force!"

# translated from $atin from Ne%ton&s

Principia Mathematica Philosophiae

Naturalis


11/19

Net Force

Vector quantit a uantity whose description reuires both magnitude

how much?/ and direction which wa?/

can be represented by arrows drawn to scale, called

vectors

6 length of arrow represents magnitude and the

arrowhead shows direction.Eamples: force, velocity, acceleration

A !calar quantit has magnitude only e.g. mass, volume, speed,etc./

Vector quantit a uantity whose description reuires both magnitude

how much?/ and direction which wa?/

can be represented by arrows drawn to scale, called

vectors

6 length of arrow represents magnitude and the

arrowhead shows direction.

Eamples: force, velocity, acceleration

A !calar quantit has magnitude only e.g. mass, volume, speed,etc./


12/19

Net Force

%he net "orce is the combination of all forces that

change an object)s state of motion.

Eample: f you pull on a bo with *+ 7 and a friendpulls oppositely with 5 7, the net force is 5 7

in the direction you are pulling.


13/19

!he "#uili$rium %ule


14/19

!he "#uili$rium %ule & "'ample

A string holding up a bag of flour

%wo forces act on the bag of flour:

%ension force acts upward. 'eight acts downward.

$oth are eual in magnitude and

opposite in direction. 'hen added, they cancel to 1ero.

!o, the bag of flour remains at rest.


15/19

Support (Normal) Force

!upport "orce or normal "orce/ is an upward

force on an object that is opposite to the force of

gravity.

Eample:

A boo# on a table compresses atoms

in the table, and the compressedatoms produce the support force.


16/19

*nderstanding Support Force

'hen you push down on a

spring, the spring pushes

bac# up on you.

!imilarly, when a boo#

pushes down on a table,

the table pushes bac# upon the boo#.


17/19

"#uili$rium of Moving !hings

Mechanical equili#rium: a state of no change in

motion with no net force acting.

− STATIC euilibrium

Eample: hoc#ey puc# at rest on slippery ice

− DYNAMIC euilibrium

Eample: hoc#ey puc# sliding at constant speed on

slippery ice


18/19

"#uili$rium of Moving !hings

$quili#rium test% whether somethingundergoes changes in motion

Eample: A crate at rest is in static euilibrium.Eample: 'hen pushed at a steady speed, it is in

dynamic euilibrium.


19/19

!he Moving "arth

8opernicus) proposed idea that

Earth is moving was refuted by

the people of that time.

E'ample: f the Earth does move,how can a bird swoop down from

a branch to catch a worm9

Solution: As it swoops, due toinertia, it continues to go side0

ways at the speed of Earth along

with the tree and the worm.

newton's first law of physics

Documents