Download Newton`s 1st Law Newton`s 2nd Law net A. B. C. D. E. Newton`s 3rd

Today’s Topics
• Newton’s Three Laws
• Mass and Weight
• Free Body Diagrams
Newton’s 2nd Law
A _______ is that which causes (unrestrained) objects to __________
Links forces to motion
We frequently can have knowledge of forces acting on an object
Can use the 2nd Law to translate the force into acceleration
Can then find velocity and position
Newton’s 1st Law
NET Force: ________________
If no NET _______ is applied to an object…
the object either remains at _______, OR
moves at a _________________
“At rest” is a special case of constant v, with v = 0!
Since _______ remains constant unless a net force is applied, objects
appear to be “_______”
Latin word for laziness: ___________
1st Law sometimes referred to as:
The graph to the left shows velocity of an object as a function of time.
Which of the graphs best shows the net force versus time for this object?
vx
ΣFx
ΣFx
ΣFx
ΣFx
ΣFx
t
0
Rolling cart – constant velocity?
t
0
A.
EF 151 Spring, 2015 Lec 2-3
Force: Scalar or vector?
Mass: Scalar or vector?
Fnet=ma
1
t
0
t
0
B.
t
0
C.
t
0
D.
E.
EF 151 Spring, 2015 Lec 2-3
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SI Units of Acceleration, Mass & Force
Newton’s 3rd Law
If one object exerts a force on a second object, the
________ object exerts a force on the _______
object
Quantity
Basis
g (at earth’s surface)
This “_________” force has a magnitude equal
to the first force
Mass
This “_________” force acts in the
_________direction as the first force
SI System
USC System
Mass-based
Force-based
9.81 m/s2
32.2 ft/s2
kg
slug
Force
N
pound
F=ma
1N = 1kg(1m/s2)
1lb = 1slug(1ft/s2)
SI System: kg linked to meter through H2O
Density of water is 1000 kg/m3 = 1 kg/L = 1 g/cm3
How are you able to stand on the floor?
How are you able to jump up off the floor?
USC System: two other force units
1 ton = 2000 lb
1 kip (kilopound) = 1000 lb
EF 151 Spring, 2015 Lec 2-3
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EF 151 Spring, 2015 Lec 2-3
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Conversion Factors
Types of Forces
Force
Field Forces (act at a distance)
1 Newton = 0.2247 lb
1 lb = 4.448 Newtons
An apple weighs about:
What is your weight in Newtons?
_____________________
_____________________
Contact Forces
Ropes, cables, string
Mass
assumed to be flexible and of negligible mass;
1 kg = 0.06846 slugs
1 slug = 14.594 kilograms
What is your mass in kg? _______ slugs? _______
tension the same everywhere
force in the direction of the rope
Normal force: ___________
Weight: force of gravity
W = ______
Lazydog weighs 43 lb on the earth and gmoon is 5.31 ft/s2
Friction force: ______________
Springs: ____________
what is the dog’s mass on the moon? _______
what is the dog’s weight on the moon? _______
EF 151 Spring, 2015 Lec 2-3
Fnet=ma
5
FBD = KD
____________________
Diagram of ______ free from
surroundings and showing all
________ that act on the body
Identify ___________
Draw ___________
Define a ______________
Draw all ________ that act ___ the body
Do not show ________________
=
EF 151 Spring, 2015 Lec 2-3
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The Original Alabama Bass Tracker
_____________________
Diagram of ______ free from
surroundings and showing
___________________ (inertial) vectors
Alabama fan weighs 195 lbs. His “boat” and
motor weigh 218 lbs and the motor provides
a force of 143 lbs. The drag resistance of the
water is 62 lbs. What is the acceleration of
the boat and the forces on the fisherman?
Draw same body
Show all __________ components
=
What is the correct FBD of the fisherman?
A.
Runner starting a race:
Ball during launch:
EF 151 Spring, 2015 Lec 2-3
B.
195 lb
195 lb+218 lb
F
7
EF 151 Spring, 2015 Lec 2-3
N
C.
195 lb
F
N
D.
195 lb
F
N
8