A presentation that tackles the relationship between machines, machine efficiency and work outputs.

1. Machines And
Efficiency
Lawrence Avillano
MagistersDesk.BlogSpot.Com

2. Efficiency
Most people think that a machine can
do work. However, a work must be put
into a machine before it can do any
work . A machine merely converts this
work into more useful work by
changing force, distance or direction.

3. o The useful work obtained by the
machine is always less than the work
input because some of it is used to
overcome friction
o The Ratio of the work output over the
work input determine the efficiency of
the machine
Efficiency

4. o A scissor a knife and can opener do
work when someone use them. In
each case, an effort force must be
applied to overcome a resistance
force.
Efficiency

5. Efficiency
 Every machine has a work input (Wi)
which is the effort force (Fe) multiplied
by the effort distance (De) and work
output (Wo) which is resistance force
(Fr) multiplied by resistance distance
(Dr)
 Wi = Fe x De and Wo = Fr x Dr

6. Calculating Efficiency
 Sample problem:
a crate is dragged up a ramp 20 meter
long(effort distance) . One end of the
ramp is on the ground. The raised end
is 5 meter long (resistance distance).
The crate has force of 300 N
(resistance force). The effort force is
100 N. find the work input and output
then solve for efficiency

7. Sample Problem
 Given:
(a) effort force – 100 N
(b) effort distance – 20 m
(c) resistance force – 300 N
(d)resistance distance – 5 m

8. Sample Problem
 Solution
Work input = Fe x De
= 100Nx20m
=2000N-m
Work output = Fr x Dr
=300 N x 5m
=1500N-m
Efficiency = work output/work input x 100
= 1500N-m/2000N-m x 100
= 75 %
Therefore the machine has an efficiency of 75 %