Chapter Nine: Simple Machines
➢9.1 Types of Simple Machines
➢9.2 Mechanical Advantage
➢9.3 Levers in the Human Body
9.3 Levers in the human body
➢The human body is a
complex machine that
includes a number of
simple machines—
levers.
➢Your arms and legs,
for example, work as
levers to move and lift
objects.
9.3 Levers in the human body
➢A classic example of a
third class lever is a
broom.
➢A broom does not
multiply force, but it does
multiply speed.
➢Since your limbs are
third class levers, they
multiply speed to do
tasks quickly.
9.3 Levers in the human body
➢Human arms and legs
are examples of third
class levers because the
input forces are between
a fulcrum and the output
force.
➢The output force is what
you accomplish with your Where is the input
force and the fulcrum?
hands and feet.
9.3 Levers in the human body
➢In the human body, all bones act as
levers and each joint can serve as a
fulcrum.
➢ When lifting your head, your neck works as a
first-class lever.
➢ When you stand on your toes, the feet act as
second-class levers.
➢ When biting, your jaw works as a third-class
lever.