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N e w t o n’ s L a w s. Unit 3. 3.1 Force and Mass. Force – push or pull; required to change an object’s motion. Vector – so magnitude and direction Example of Contact Forces Friction Tension Applied Spring. Examples of Field Forces Gravitational Electric Magnetic. - PowerPoint PPT Presentation
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Newton’s
LawsUnit 3
3.1 Force and Mass
3.1 Force and mass
Force – push or pull; required to change an object’s motion.
Vector – so magnitude and direction
Example of Contact Forces
Friction
Tension
Applied
Spring
Examples of Field Forces
Gravitational
Electric
Magnetic
3.1 Force and mass
Mass – measurement of how difficult it is to change the objects velocity
Inertia – resistance to change in velocity
So mass is a measurement of an object’s inertia
3.2 Newton’s First Law of Motion
3.2 Newton’s First Law of Motion
1st Law
An object at rest remains at rest as long as no net force acts on it.
An object moving with constant velocity continues to move with the same speed and in the same direction as long as no net force acts on it.
3.2 Newton’s First Law of Motion
Sometimes called the Law of Inertia
3.3 Newton’s Second Law of Motion
3.3 Newton’s Second Law of Motion
2nd Law
A net force causes an acceleration in the direction of the net force.
amF
Simulation
3.3 Newton’s Second Law of Motion
Free body diagrams
Show all the forces acting on an object
For example an object sitting on a table
W – weight = mg
N – Normal Force (perpendicular) to the surface
N
W
3.3 Newton’s Second Law of Motion
Free body diagrams
If a rope pulls the object toward the right, then
T = Tension
N
W
T
Practice Free Body
3.3 Newton’s Second Law of Motion
Free body diagrams
Steps in problems solving
1.Sketch the forces
2.Isolate the Object
3.Choose a Coordinate System
4.Resolve the Forces into Components
5.Apply Newton’s Second Law of Motion
3.3 Newton’s Second Law of Motion
A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?
3.3 Newton’s Second Law of Motion
A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?
Free Body
diagram
3.3 Newton’s Second Law of Motion
A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?
Free Body
diagram
N
W
T
3.3 Newton’s Second Law of Motion
A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?
Free Body
diagram
Axis
N
W
T
3.3 Newton’s Second Law of Motion
A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?
Free Body
diagram
Axis
N
W
T
Ty
Tx
3.3 Newton’s Second Law of Motion
A 50 kg gopher has a string tied around his neck and pulled with a force of 80 N at an angle of 30o to the horizontal. What is his acceleration?
Free Body
diagram
Axis
Equation
N
W
Ty
Tx
yyy
xxx
maWNTF
maTF
0sin
cos
WNT
maT
239.1
5030cos80
sma
a
3.4 Newton’s Third Law of Motion
3.4 Newton’s Third Law of Motion
For every force that acts on an object, there is a reaction force acting on a different object that is equal in magnitude and opposite in direction.
If object 1 exerts a force F on object 2, then object 2 exerts a force –F on object 1.
3.4 Newton’s Third Law of Motion
What are the action reaction pairs in the following?
3.4 Newton’s Third Law of Motion
A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg.
A.What is the acceleration of
the man?
B. What is the acceleration of the canoe?
3.4 Newton’s Third Law of Motion
A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg.
Free Body Diagrams
P
Nc
Wc
P
Wm
Nm
3.4 Newton’s Third Law of Motion
A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg.
Equations
P
Nc
Wc
P
Wm
Nm0
ccy
cx
WNF
amPF0
mmy
mx
WNF
amPF
3.4 Newton’s Third Law of Motion
A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg.
A-acceleration of man
P
Nc
Wc
P
Wm
Nm0
ccy
cx
WNF
amPF 233.0
6020
sm
m
a
a
amP
3.4 Newton’s Third Law of Motion
A 60 kg man walks off a 3 m long canoe by walking from one end to the other. He applies a force of 20 N to the canoe, which has a mass of 150 kg.
A – acceleration of canoe
P
Nc
Wc
P
Wm
Nm
213.0
15020
sm
c
a
a
amP
233.0
6020
sm
m
a
a
amP
3.4 Newton’s Third Law of Motion
Two boxes are tied together with a rope, and the first one is pulled by a second rope. Both boxes accelerate at 2.0 m/s2. If the front box has a mass of 25 kg, and the second a mass of 50 kg, what is the tension on each rope?
a
3.4 Newton’s Third Law of Motion
Free body diagrams
Nf
Wf
T1
T2
Wb
Nb
T2
3.4 Newton’s Third Law of Motion
Equations
Solve (add)
Nf
Wf
T1
T2
Wb
Nb
T2
02
bby
bx
WNF
amTF
0
21
ffy
fx
WNF
amTTF
amTT
amT
f
b
21
2
NT
T
ammT bf
150
2)5025(
)(
1
1
1
N
kgTs
m
100
2)50( 22
3.5 The Vector Nature of Forces
3.5 The Vector Nature of Forces
Forces are vectors, so they can be treated using vectors rules
3.5 The Vector Nature of Forces
Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?
Free Body Diagram?
W
LB
3.5 The Vector Nature of Forces
Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?
Components?
W
LB By
Bx
3.5 The Vector Nature of Forces
Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?
Components?
W
LBy
Bx
Ly
Lx
3.5 The Vector Nature of Forces
Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?
Equations?
W
By
Bx
Ly
Lx
yyyy
xxxx
maWBLF
maBLF
3.5 The Vector Nature of Forces
Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?
Values?
W
By
Bx
Ly
Lx
yyyy
xxxx
maWBLF
maBLF
3.5 The Vector Nature of Forces
Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?
Values?
W
By
Bx
Ly
Lx
0sin
0cos
mgBL
BL
y
x
3.5 The Vector Nature of Forces
Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 7N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?
Solve?
W
By
Bx
Ly
Lx
0sin
0cos
mgBL
BL
y
x
3.5 The Vector Nature of Forces
Two men are carrying a 1.3 kg pail of water, the first dude (Bob) exerts a force of 12.3N, and the second one (Leon) exerts a force of 11N @ 28o. What is the angle of Bob’s force?
Solve?
W
By
Bx
Ly
Lx
6.7
7.9
)8.9)(3.1(28sin11
28cos11
y
x
y
x
B
B
B
B
o387.9
6.7tan 1
3.6 Frictional Forces
3.6 Frictional Forces
Friction – force that opposes motion
Caused by microscopic irregularities of a surface
Increases as pushing
force increases
3.6 Frictional Forces
Depends on the normal force and the type of surface
f – force of friction (N)
N – normal force
– coefficient of friction (1 or less)
Nf
3.6 Frictional Forces
Three types of friction
1.Static – object at rest
2.Kinetic – object in motion
3.Rolling – just like it sounds
Surfaces µ (static) µ (kinetic)
Steel on steel 0.74 0.57
Glass on glass 0.94 0.4
Metal on Metal (lubricated) 0.15 0.06
Ice on ice 0.1 0.03
Teflon on Teflon 0.04 0.04
Tire on concrete 1 0.8
Tire on wet road 0.6 0.4
Tire on snow 0.3 0.2
3.6 Frictional Forces
Example
