Download Newton`s 1st Law Newton`s 2nd Law net Newton`s 3rd Law SI Units

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
Newton’s 1st Law
 We frequently can have knowledge of forces acting on an object
 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:
 Can use the 2nd Law to translate the force into acceleration
 Can then find velocity and position
Fnet=ma
Force: Scalar or vector?
Mass: Scalar or vector?
 Rolling cart – constant velocity?
EF 151 Spring, 2017 Lec 2-3
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EF 151 Spring, 2017 Lec 2-3
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
Basis
 This “_________” force has a magnitude equal
to the first force
g (at earth’s surface)
 This “_________” force acts in the
_________direction as the first force
Quantity
SI System
USC System
Mass-based
Force-based
9.81 m/s2
32.2 ft/s2
Mass
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
A couple of weeks ago we dropped a 10 ton wrecking
ball onto a Mini Cooper. Which object experienced
the greater force during that collision?
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EF 151 Spring, 2017 Lec 2-3
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FBD = KD
Conversion Factors / Weight
 Force
 1 Newton = 0.2247 lb (~1/4 lb)
 1 lb = 4.448 Newtons (~4.5 N)
 What is a 200 lb professor’s weight in Newtons? _______
____________________
Diagram of ______ free from
surroundings and showing all
________ that act on the body
 Mass
 1 slug = 14.594 kilograms
 What is a 30 kg dog’s mass in slugs? _______
Weight: force of gravity





W = ______
 Mass of an object is same everywhere - weight depends on location
 200 lb on earth has a mass of ________
 30 kg on earth has a weight of ________
Identify ___________
Draw ___________
Define a ______________
Draw all ________ that act ___ the body
Do not show ________________
=
=
_____________________
Diagram of ______ free from
surroundings and showing
___________________ (inertial) vectors
 Draw same body
 Show all __________ components
Runner starting a race:
Lazydog weighs 64 lb on the earth and gmoon is 5.31 ft/s2
 what is the dog’s mass on the moon? __________ slugs __________ kg
Ball being thrown:
 what is the dog’s weight on the moon? ___________ lb ___________ N
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The Original Alabama Bass Tracker
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The Original Alabama Bass Tracker
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.
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?
What are the forces on the fisherman?
What mass is used for kinetic diagram?
EF 151 Spring, 2017 Lec 2-3
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EF 151 Spring, 2017 Lec 2-3
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