work & machines. work work transfer of energy through motion force exerted through a __________...
TRANSCRIPT
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Work & Machines
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Work Work
transfer of energy through motionforce exerted through a
__________
W = Fd
Distance must be in direction of ______!
W: work (___)F: force (____)d: distance (__)
1 J = 1 N·mFWd
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Try these!!! A mover lifts a 98 N box 1.8 m from the
ground to a shelf. How much work is done on the box?
Alice has a heavy pocketbook. Each morning to lifts it off the ground and puts it on the counter that is 1.6 m from the floor. In doing this she does 8 J of work. How much does the pocketbook weigh?
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PracticePick up a Work worksheet from the front table & complete #1-10
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Do you want to do all the work yourself?
Of course not!What do we use that helps us do
work?
MACHINES!!!
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Machines Machines Machines Machines II. The Simple Machines
Lever Pulley Wheel & Axle
Inclined Plane Screw Wedge
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http://www.youtube.com/watch?v=grWIC9VsFY4&safety_mode=true&persist_safety_mode=1
http://www.youtube.com/watch?v=qybUFnY7Y8w&safety_mode=true&persist_safety_mode=1
http://www.youtube.com/watch?v=lCYg_gz4fDo&safety_mode=true&persist_safety_mode=1
http://rubegoldberg.com/
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A. LeverLever
a bar that is free to pivot about a fixed point, or ____________
“Give me a place to stand and I will move the Earth.”
– Archimedes
Engraving from Mechanics Magazine, London, 1824
Effort arm
Resistancearm
________
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Lever Ideal Mechanical Advantage (IMA)
frictionless machine
r
e
L
LIMA
Effort arm length
Resistancearm length
Le must be greater than Lr in order to multiply the force.
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LeverFirst Class Lever
can increase force, distance, or neither
changes direction of force
r
e
L
LIMA
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LeverSecond Class Lever
always increases __________.
r
e
L
LIMA
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LeverThird Class Levers
always increases __________.
r
e
L
LIMA
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PulleyPulley
grooved wheel with a ______ or chain running along the groove
a “flexible first-class lever”
LeLr
F
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Pulley Ideal Mechanical Advantage (IMA)
equal to the number of supporting ____________
IMA = 0 IMA = 1 IMA = 2
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PulleyFixed Pulley
IMA = ____
does not increase force
changes direction of force
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PulleyMovable Pulley
IMA = ____increases force
doesn’t change direction
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B. PulleyBlock & Tackle
combination of fixed & movable pulleys increases force (IMA = 4) may or may not change ___________
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Wheel and AxleWheel and Axle
two wheels of _________sizes that rotate together
a pair of “rotatinglevers”
Wheel
Axle
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Wheel and Axle Ideal Mechanical Advantage (IMA)
effort force is usu. applied to wheel
axle moves less _________ but with greater force
r
e
r
rIMA
effort radius
resistance radius
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Problems You use a 160 cm plank to lift a large
rock. If the rock is 20 cm from the fulcrum, what is the plank’s IMA?
GIVEN:
Lr = 20 cm
Le = 140 cm
IMA = ?
WORK:
IMA = Le ÷ Lr
IMA = (140 cm) ÷ (20 cm)
IMA = 7
IMA
Le
Lr
20cm
160cm
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Problems A crank on a pasta maker has a radius
of 20 cm. The turning shaft has a radius of 5 cm. What is the IMA of this wheel and axle?
GIVEN:
re = 20 cm
rr = 5 cm
IMA = ?
WORK:
IMA = re ÷ rr
IMA = (20 cm) ÷ (5 cm)
IMA = 4
IMA
re
rr
5 cm 20 cm