Transcript machines

Chapter
machines
Machines
A device used to multiply
forces
or simply to change the
direction of forces
Components of Machines
Lever…a bar that is free to pivot,
or turn, about a fixed point
Fulcrum….Fixed point of the
Lever
Effort Arm….Part of lever on
which the effort force is applied
Resistance arm…. Part of the
lever that exerts the resistance
force
Type I or First Class Lever
The fulcrum between the force
and the load, or between input and
output.
Type II or Second Class Lever
Reverse the position of the load
and the fulcrum.
The load is in between the fulcrum
and the effort force.
Type III or Third Class Lever
Fulcrum is at one end the load is
at the other end….Input force is
applied between them
Machines
D
N
M
F
d
Fulcrum
Work = F
D = Nd
Mg
Pulley
A Kind of a lever that can be used
to change the direction of a force.
Mechanical advantage
The ratio of resistance force to effort force
MA = Fr/Fe
Fe….effort force
Fr…..resistance force
Ideal Mechanical advantage
Workout = Workin
 Frdr = Fede
IMA = de/dr
Efficiency
Workout = Workin
 efficiency = wo/ Wi X 100%
Compound Machines
Consists of two or more simple
machines linked…..
so that the resistance force of one
machine………
becomes the effort force of the
second.
Rube-Goldberg
Machines - An Application of
Energy Conservation
If there is no mechanical energy
losses then for a simple
machine...
work input = work output
(F
d)input = (F d)output
Examples - levers and tire jacks
Efficiency
work done
Efficiency 
energy used
Useful energy becomes wasted
energy with inefficiency.
Heat is the graveyard of useful
energy.
Comparison of Kinetic Energy
and Momentum
Kinetic energy is a scalar quantity.
Momentum is a vector quantity.
Discuss rubber bullets as
compared to lead bullets.
Example Questions
A 10 lb weight is lifted 5 ft. A 20 lb weight
is lifted 2.5 ft. Which lifting required the
most work?
(a) 10 lb weight
(b) 20 lb weight
(c) same work for each lifting
(d) not enough information is given to work
the problem
An object of mass 6 kg is traveling at a
velocity of 30 m/s. How much total work
was required to obtain this velocity starting
from a position of rest?
(a) 180 Joules
(b) 2700 Joules
(c) 36 Joules
(d) 5 Joules
(e) 180 N
A 20 Newton weight is lifted 4 meters.
The change in potential energy of the
weight in Newton.meters is
(a) 20
(b) 24
(c) 16
(d) 80
(e) 5