Transcript Simple Machines - Mr. Hounslow's Physics Page

Work, Mechanical
Advantage and Efficiency
Essential Question: What is the
relationship between IMA & MA
 All machines can be classified as or a
combination of levers and inclined planes.
 Manipulate the Law of Conservation of Energy
 The amount of energy that goes in the machine =
to the amount of energy that comes out.
 Work in = Work out
 Fin x d in = F out x d out
 Machines DO NOT decrease work!!!
 They change the Force and distance needed
to get a certain amount of work done.
F
d
F
d
F
d
F in x d in = F out x d out
Fin x 1.75 m = 2000 N x 0.25 m
Fin = 2000 N x 0.25 m
Fout
1.75 m
Fin = 286 N
2000 N
d in= 1.75 m
Fulcrum/
Pivot point
d out= 0.25 m
 How much a machine changes the force
 There are 4 variables
 Fe = “effort force”: how much YOU put in.
 Fr = “resistance force”: force generated by
machine.
 de = “distance effort”: distance effort must
travel i.e. length of a lever’s effort arm.
 dr = “distance resistance”: distance the
resistance must travel i.e. the length of the
resistance arm in a lever.
Fr
Fe
de
Fulcrum/
Pivot point
dr
 Model of a machine in an “ideal”
world.
 No friction or heat loss.
 Ideal mechanical advantage =
distance effort/distance resistance
 IMA = de/dr
 This is a ratio so there are no units
In the “real” world energy
is lost as friction and heat.
Mechanical Advantage =
resistance force/effort force
MA = Fr/Fe
No units
Workout / Workin x 100
The ratio of a machine’s MA
to its IMA determines its
efficiency.
Efficiency = MA / IMA x 100.
 Label
 3 lever types
 Class 1 lever:
 Ex: crowbar




Fe = “effort force”
Fr = “resistance force”
de = “distance effort”
dr = “distance resistance”
Fe
Fr
de
dr
Fulcrum/
Pivot point
 Label




 Class 2 lever:
 Ex: wheel barrow
Fe = “effort force”
Fr = “resistance force”
de = “distance effort”
dr = “distance resistance”
Fr
dr
Fulcrum/
Pivot point
de
Fe
 Label




Class 3 lever:
 Ex: bicep
Fe = “effort force”
Fr = “resistance force”
de = “distance effort”
dr = “distance resistance”
Fr
de
Fulcrum/
Pivot point
Fe
dr
 Example: ramp
dr
Fr
 Wedge:
Inclined plane
 Screw:
Inclined plane wrapped
around a cylinder
 Wheel and axle: Lever
 Pulley:
Variation of wheel and
axle
Height does not change, only the angle.
Height =
0.5 m
Scale reads = 300g
Car mass = 500g
Height =
0.5 m
Length =
0.83 m
300
Modified test
Scale reads = 3N
Car mass = 5N
Height =
0.5 m
Length =
0.83 m
300
Scale reads = 300g
Car mass = 400g
Height =
0.5 m
Length =
0.66 m
300
Inclined Plane
Distance
Force
Force
Distance
• Example: ramp
dr
Fr
200 N
Fe
Fr
1m
4m
dr
de
75N
Class 1 lever
Class 2 lever
Fr
Fe
dr
de
Fe
Fr
de
dr
Fr
dr
Class 3 lever
Fe
Fe
de
de
Fr
dr
Force
Resistance
Fulcrum