Page 54 - Science Course 2 (Book 2)
P. 54
Mo9-L2c: What is Mechanical Ef ciency?
Input and output work are measured in joules.
Ef ciency is expressed as a percentage by
multiplying the ratio by 100%.
A B C
Newton’s Laws and Simple Machines
Input Force 5N 5N 5N
Newton’s third law says that if one object applies a
force on a second object, the second object applies
Output Force 10N 15N 20N an equal and opposite force on the f rst object.
Mechanical 2 3 4
Advantage
The ef ciency of a machine is never 100%—some
work is always transformed into wasted thermal
energy because of friction.
Lubricating the moving parts of a machine reduces
the friction between the moving parts so that less
input work is transformed to waste energy.
According to Newton’s f rst law, the motion of an
object changes when the forces that act on the
object are unbalanced.
According to Newton’s second law of motion, the
change in motion of an object is in the same
direction as the total, or net.
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