Download Machines

Machines
Objectives
1. define machine, mechanical advantage,
ideal mechanical advantage and
efficiency, lever, pulley, fulcrum
2. describe inclined planes, levers and pulleys
3. explain how machines demonstrate the
Law of Conservation of Energy
4. calculate the efficiency of simple machines
Definition
any device that multiples and/or changes the
direction of an applied force
Examples
1.) inclined plane (ramp)
2.) lever – bar that rotates about a fixed point
(fulcrum)
3.) pulley – lever that rotates in a full circle
There are three types of levers
They differ on location of the fulcrum, load and
effort.
Fulcrum – pivot point
Load – what is to be lifted
Effort – where the force is applied
Class I Lever
Load, Fulcrum, Effort
Class II Lever
Fulcrum, Load, Effort
Class III
Fulcrum, Effort, Load
Pulley
• lever that rotates in a full circle
• effectiveness is function of the number
supporting ropes
• Can only multiply the force when direction is
changed by 180º
Machines & the Law of Conservation
of Energy
• Workin = Workout
Findin = Foutdout
Key:
Fin = input force (the force that you exert)
din = input distance (the distance that you move)
Fout = output force (the force that the machine exerts)
dout = output distance (the distance that the object moves)
• usually trade off lesser input force for greater
input distance
Machines demonstrate the Law of
Conservation of Energy
• The reason for using a machine is to decrease
the amount of force needed to lift an object
– This is called the mechanical advantage of the
machine
• The payback for this decrease in force is an
increase in the distance that the original force
must be applied over
– This is called the ideal mechanical advantage
The machine does work and the person
using the machine does work
• The machine cannot do more work than the
person.
• The comparison of the machines work to the
persons work is the efficiency
Mechanical Advantage
•
•
•
•
ratio of output force to input force
number has no unit
given as a whole number
Equation
MA = Fout/Fin
Ideal Mechanical Advantage
•
•
•
•
ratio of input distance to output distance
number has no unit
given as a whole number
Equation
IMA = din/dout
Efficiency
• ratio of mechanical advantage to ideal
mechanical advantage
• number is given as a percentage
• Equation
Eff = MA÷IMA x 100
1.) You use a 105 N force over a 10 m distance to move a 400 N
box up 2.2 m. What is the efficiency?
• Data
• Equations
• Substitute & Solve
• Answer
Fout = 400 N
Fin = 105 N
din = 10 m
dout = 2.2 m
Eff = MA ÷ IMA x100
MA = Fout ÷ Fin
IMA = din ÷ dout
MA = 400 ÷ 105 = 3.81 = 4
IMA = 10 ÷ 2.2 = 4.76 = 5
EFF = 4 ÷ 5 x 100
80 %
2.) A ramp is 25 m long a 3.5 meters high. On it, you can pull a
250 N crate with only 49 N. What is the efficiency?
• Data
• Equations
• Substitute & Solve
• Answer
Fout = 250 N
Fin = 49 N
din = 25 m
dout = 3.5 m
Eff = MA ÷ IMA x100
MA = Fout ÷ Fin
IMA = din ÷ dout
MA = 250 ÷ 49 = 5.10 = 5
IMA = 25 ÷ 3.5 = 7.14 = 7
EFF = 5 ÷ 7 x 100
71.4 %
3.) You can lift a 325 N piano up 10.3 m with 53 N if you use a
pulley system and pull 73 m or rope. What is the efficiency?
• Data
• Equations
• Substitute & Solve
• Answer
Fout = 325 N
Fin = 53 N
din = 73 m
dout = 10.3 m
Eff = MA ÷ IMA x100
MA = Fout ÷ Fin
IMA = din ÷ dout
MA = 325 ÷ 53 = 6.13 = 6
IMA = 73 ÷ 10.3 = 7.09 = 7
EFF = 6 ÷ 7 x 100
85.7 %