SIMPLE MACHINES 9.3

Chapter Nine: Simple Machines

9.1 Types of Simple Machines

9.2 Mechanical Advantage

9.3 Levers in the Human Body

Chapter 9.3 Learning Goals

Locate human body parts that act as levers.

Classify human body as first, second, or third class levers.

Investigation 9B

Key Question:What types of levers does your body have?

Levers and the Human Body

9.3 Levers in the human bodyThe 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 bodyHuman 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 hands and feet.

Where is the input force and the fulcrum?

9.3 Levers in the human bodyIn 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.

Investigation 9C

Key Question: What is mechanical

advantage, and how do ropes and pulleys give you mechanical advantage?

Mechanical Advantage

Prosthetics in ActionHugh Herr, Ph.D., a

physicist and engineer studies biomechanics and prosthetic technology. In addition to holding several patents in this field, he has developed highly specialized feet for rock climbing that are small and thin.