9-2 Notes – The Body and Levers Chapter 9, Lesson 2

Levers A lever is a simple machine made of anything rigid that pivots around a fixed point.

Levers A fulcrum is the fixed point that a lever pivots around, called the pivot point.

Levers Levers are used to make difficult jobs easier: to lift heavy objects or move objects faster or farther.

Levers Two forces act upon different parts of a lever: effort force and resistance force

Levers The effort force is the force YOU exert on a lever. The resistance force is the force that the lever exerts on the object.

Levers in the Body Most bones and muscles work together as lever system.

Levers in the Body Your limbs contain multiple joints and therefore multiple levers.

Levers in the Body A bone is the lever, a joint is the fulcrum, and muscles are the effort force

Levers in the Body The length of a lever affects the way your body works.

First-Class Lever The fulcrum is in the center, between the resistance force and effort force. Examples: scissors, seesaws, neck

First-Class Lever

Second-Class Lever The resistance force is in the center, between the fulcrum and effort force. Example: wheelbarrow, toes

Second-Class Lever

Third-Class Lever The effort force is in the center, between the resistance force and fulcrum. Examples: rake, tweezers, elbow

Third-Class Lever fulcrum effort resistance

Third-Class Lever

1 F ulcrum 2 R esistance 3 E ffort It rhymes! (which is in the center)

Mechanical Advantage Mechanical advantage (MA) is the ability of a machine to increase the amount of force put into the machine.

Mechanical Advantage MA = 0.5 m / 1.5 m

Try This!!! 1.Slide your index finger under a textbook, and try to lift it. 2.Now slide a ruler 2 inches under the textbook. Put your index finger on the free end of the ruler, and try to lift the book by pushing down on the ruler. 3.Now try it with HALF the ruler under the book. What’s easiest?

Try This!!! The ruler is a lever. The fulcrum is the end of the ruler under the book. The force you applied to the ruler is the effort force. The resistance force is the force that the book exerts, trying NOT to be lifted. The ruler gives you mechanical advantage (MA) and makes it easier for you to lift the book.

What determines how easy or hard it will be to use a particular lever? Athe class of lever Bthe distance between the fulcrum and the effort force Cthe distance between the effort force and the resistance force Dthe distance between the forces and the fulcrum 9.2 The Body and Levers 1.A 2.B 3.C 4.D

What type of lever is a wheelbarrow? Afirst-class Bsecond-class Cthird-class Dfourth-class 9.2 The Body and Levers 1.A 2.B 3.C 4.D

What is the mechanical advantage of a lever if the effort force is 4 m from the fulcrum, and the resistance force is 8 m from the fulcrum? A0.5 B1.5 C2C2 D4D4 9.2 The Body and Levers 1.A 2.B 3.C 4.D

What type of lever has the resistance force between the fulcrum and the effort force? Afirst-class Bsecond-class Cthird-class Dnone of the above 1.A 2.B 3.C 4.D

What function does the resistance force of a lever perform? Amoves objects around a point Bmoves an object over a distance Copposes the effort force Dprovides the pivot point 1.A 2.B 3.C 4.D

What is the advantage of a third-class lever? Aallows faster or farther movement of objects Ballows movement of objects using less force Cdoes not require a resistance force Dis a more stable arrangement SCI 6.i 1.A 2.B 3.C 4.D

A rake is an example of what kind of lever? Afirst-class Bsecond-class Cthird-class Dboth A and C SCI 6.i 1.A 2.B 3.C 4.D

Vocab – The Body & Levers TB pages: work 2.lever 3.fulcrum 4.first-class lever 5.second-class lever 6.third-class lever 7.mechanical advantage