Transcript Simple Machines - Mr. Hounslow's Physics Page

Simple Machines
Work, Mechanical Advantage
and Efficiency
Simple Machines
 All machines can be classified as or a
combination of levers and inclined planes.
 Manipulates 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 and Work
 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
Work Done
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
Mechanical Advantage
 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.
Mechanical Advantage
Fr
Fe
de
Fulcrum/
Pivot point
dr
Ideal Mechanical Advantage
 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
Mechanical Advantage
 In the “real” world energy is
lost as friction and heat.
 Mechanical Advantage =
resistance force/effort force
 MA = Fr/Fe
 No units
Efficiency
Workout / Workin x 100
The ratio of a machine’s
MA to its IMA determines
its efficiency.
Efficiency = MA / IMA x
100.
Levers
 3 lever types
 Class 1 lever:
 Ex: crowbar
 Label




Fe
Fr
de
dr
Fulcrum/
Pivot point
Fe = “effort force”
Fr = “resistance force”
de = “distance effort”
dr = “distance resistance”
Levers
 Class 2 lever:
 Ex: wheel barrow
 Label
Fr




Fe = “effort force”
Fr = “resistance force”
de = “distance effort”
dr = “distance resistance”
dr
Fulcrum/
Pivot point
de
Fe
Levers
 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
Inclined Plane
 Example: ramp
dr
Fr
More simple machines
 Wedge:
Inclined plane
 Screw:
Inclined plane
wrapped around a
cylinder
 Wheel and
Lever
axle:
 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
Mechanical Advantage
Example
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