FORCE MOTION Simple Machines

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FORCEMOTIONSimple Machines
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SI units

• mass kilogram (kg)
• distance meter (m)
• time second (s)
• velocity or speed m/s
• acceleration m/s/s m/s2
• force newton (N) 1 kgm/s2
• energy joule (J) 1 Nm 1 kgm2/s2

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balanced forces

• Net force 0
• No change in motion
• (Newtons first law) (Galileos law of inertia)

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InertiaResistance to change

• Equilibrium
• Net Force Zero

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Newtons 2nd Law

• F ma
• F force
• m mass
• a acceleration
• Page 161

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Weight (Force of gravity on an object.)Symbol
Fg

• F ma
• If a g
• Then Fg mg

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Gravity

• On the surface of the earth
• g 9.8 m/s2

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Newtons 3rd Law

• Forces are always in balanced pairs.
• Textbook page 163
• See Figures 6 7

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Universal Gravitation

• Textbook page 136 137The big blue letters.
• Figures 3, 4, 5

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FRICTIONA force that resists the relative
motion or tendency to such motion of two bodies
in contact.
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A special situation

• When an object moves through air it runs into air
  molecules.
• The friction with those air molecules is called
  air resistance.

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A special situation

• When the Ffa Fg, Fnet 0 ?

Fg
Ffa
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A special situation

• When the Ffa Fg, Fnet 0
• The object stops accelerating and travels at
  constant velocity.
• Terminal velocity

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Simple Machines

• Mechanical Advantage
• MA force out force in
• How to increase for each machine?

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Simple Machines

• Three classes of levers

http//www.professorbeaker.com/lever_fact.html
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(No Transcript)
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3 classes of pulleys
Block and tackle
http//www.uq.edu.au/_School_Science_Lessons/21.5
.0.GIF
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inclined plane
O U T P U T
Input or effort force
http//www.clear.rice.edu/elec201/Book/images/img7
0.gif
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wheel and axle
http//01.edu-cdn.com/files/89501_89600/89547/file
_89547.jpg
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screw
http//www.clear.rice.edu/elec201/Book/basic_mech.
html
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wedge
output force
output force
http//www.oocities.org/jaywilliams.geo/simmach.ht
ml
http//www.clear.rice.edu/elec201/Book/basic_mech.
html
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Equations

• vavg ?d/?t
• aavg ?v/?t
• F ma
• g 9.8 m/s2