Transcript Using Machines

Machines
Ch 5 Sect 2
Machine
 Device that makes doing work easier
 Machines do not have to be complicated
 Machines can work in 3 different ways
Ways Machines Work
1. Increase amount of force being applied
•
Use a machine to increase leverage which
makes doing work seem easier
Ways Machines Work
2. Increase distance
•
By increasing distance you use a smaller
amount of force over a longer distance
moving van
Ways Machines Work
3. Changing Direction
chopping wood
Forces and Machines
 Effort force is the force that is applied to
the machine (you apply force)
 Represented by Fe
 Resistance force is the force applied by
the machine to over come resistance
(machine applies force)
 Represented by Fr
 Machine can move obj. that resist motion
Forces and Work
 Effort force is transformed to input work
 Input work is done by you (w-in)
 Resistance force is transformed to output
work
 Output work is done by the machine (w-out)
 nail removal
Machines and Energy
 Machines work based on the transfer of
energy
 You transfer energy to the machine
 The machine then transfers the energy to
the object being worked on
Machines and the Law of
Conservation of Energy
 Conservation of energy states that
energy can never be created or
destroyed, therefore the machine can
never create extra energy
 Machine can never give more energy then it
receives
 w-out can never be greater then w-in
Ideal Machines
 An ideal machine is a machine in which
all input work is transferred to useable
output work
 w-in = w-out
 No work/energy would be wasted
Efficiency
 Measure of how much work put in to a
machine is changed to useable out put
work
 Efficiency can never be more than 100%
 Humans are about 30-35% efficient
 Gas powered cars are about 7-12% efficient
 Increase efficiency by decreasing friction
Calculating Efficiency
 Work out / work in x 100 = %
 Out put work is always less then input
work so efficiency will be less then 100%
Mechanical Advantage (MA)
 The number of times a machine
multiplies the effort force
 To find MA you divide Fr by Fe
 MA=Fr/Fe
 If you are only changing the direction of
the force MA always equals one