newton's first law of physics
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Chapter 2:
Newton's 1st
Law of
Chapter 2:
Newton's 1st
Law of
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Figure 2.5
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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.
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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.
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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.
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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/.
Galileo’s Concept of Inertia
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Galileo’s Concept of Inertia
$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
.
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Figure 2.4
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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 $atin from Ne%ton&s
Principia Mathematica Philosophiae
Naturalis
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Net Force
Vector quantit a uantity whose description reuires both magnitude
how much?/ and direction which wa?/
can be represented by arrows drawn to scale, called
vectors
6 length of arrow represents magnitude and the
arrowhead shows direction.Eamples: force, velocity, acceleration
A !calar quantit has magnitude only e.g. mass, volume, speed,etc./
Vector quantit a uantity whose description reuires both magnitude
how much?/ and direction which wa?/
can be represented by arrows drawn to scale, called
vectors
6 length of arrow represents magnitude and the
arrowhead shows direction.
Eamples: force, velocity, acceleration
A !calar quantit has magnitude only e.g. mass, volume, speed,etc./
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Net Force
%he net "orce is the combination of all forces that
change an object)s state of motion.
Eample: f you pull on a bo with *+ 7 and a friendpulls oppositely with 5 7, the net force is 5 7
in the direction you are pulling.
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!he "#uili$rium %ule
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!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.
$oth are eual in magnitude and
opposite in direction. 'hen added, they cancel to 1ero.
!o, the bag of flour remains at rest.
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Support (Normal) Force
!upport "orce or normal "orce/ is an upward
force on an object that is opposite to the force of
gravity.
Eample:
A boo# on a table compresses atoms
in the table, and the compressedatoms produce the support force.
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*nderstanding Support Force
'hen you push down on a
spring, the spring pushes
bac# up on you.
!imilarly, when a boo#
pushes down on a table,
the table pushes bac# upon the boo#.
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"#uili$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
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"#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.
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!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.
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