Machines and the Body

1. Machines and the Body By, Vijaya George

2. Machines • Machines are a device that allows you to do work in a way that is easier or more effective. • Ex. If you wanted to work on a house you could use a bulldozer to make part of the job go faster.

3. Machines

4. Levers • A lever is a rigid rod that is free to rotate around a fixed pivot point • The fixed point that a lever rotates around is a fulcrum.

5. Different Classes of Levers • There are three classes of levers • These are defined by the location of the fulcrum relative to the effort force and resistance force • In a first class lever, the fulcrum is between the effort force and the resistance force • In a second class lever, the resistance force is between the effort force and the fulcrum • In a third class lever, the effort force is between the resistance force and the fulcrum

6. Levers

7. Forceand Work in Levers • A lever makes work easier by changing the amount of force exerted, the distance over which the force is exerted, or the direction of the force. • The effort you exert on a lever is called the effort force. • The distance you push down is the effort distance. • The force that the lever exerts on an object is called the resistance force. • The distance the lever pushes up on an object is the resistance distance. • The relationship between work done on a lever and the work does on a object is the formula: • EFFORT FORCE x EFFORT DISTANCE = RESISTANCE FORCE x RESISTANCE DISTANCE

8. Mechanical Advantage in Levers • A lever’s mechanical advantage is the number of times a lever increases a force exerted on it. • The mechanical advantage of a lever is equal to the ratio of resistance for to the effort force: • MECHANICAL ADVANTAGE= RESISTANCE FORCE/ EFFORT FORCE

9. The Law of the Lever • The distance from the fulcrum to the effort force is called the effort arm • The distance from the fulcrum to the resistance force is the resistance arm. • The law of the lever states, that for a lever to be balanced, the effort force times the effort arm must be equal to the resistance force times the resistance arm.

10. Joints as Machine Structures • Many of the body’s movable joints are actually fulcrums • The joints in the body act as pivot points for the bones • The bones act as levers, and muscles provide the force. • Your thigh, wrist, shoulder, knee, and elbow joint are all third class levers • The thigh and shoulder is an example of a ball and socket joint • Your wrist joint is an example of sliding joint • Your elbow and wrist joints are examples of hinge joints.

11. Joints as Machine Structures

12. Your Bones and Muscles as Lever Systems • The most common types of levers in your body is the third class lever. • But your body also has first and second class levers as well • There is always a lever where the effort force is applied at the point where a muscle attaches to a bone • The bone serves as a the lever, and the resistance force is the force exerted by the bone • The force may be used for many things like chewing, running, or lifting many things • Examples of different levers: • A first class lever is your neck • A second class lever is the call of your feet • A third class lever is your elbow

13. Your Bones and Muscles as Lever Systems

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