Chapter 13 Section 4Get book and Open to

page 532

Anticipatory Set

Machines and the Body

Big Idea

California StandardsScience Standard 6.h; 6.i

Students know how to compare joints in the body (wrist, shoulder, thigh) with structures used in machines and simple devices (hinge, ball-and-socket, and sliding joints).

Students know how levers confer mechanical advantage and how the application of this principle applies to the musculoskeletal system.

InputForce: the push or pull of an object.Work: when you exert a force on an object

that causes the object to move some distance in the same direction as the force.

Machine: a device that allows you to do work in a way that is easier and more effective.

Lever: a rigid rod that is free to rotate around a fixed pivot point.

InputFulcrum: the fixed point that a level rotates

aroundEffort force: the force that you exert on a

lever.Effort distance: the distance that you push

down.Resistance force: the force that a lever

exerts on an object.Resistance distance: the distance the lever

pushes up on an object.

InputMechanical advantage: the number of times

a lever increases a force exerted on it.Effort arm: the distance from the fulcrum to

the effort force.Resistance arm: the distance from the

fulcrum to the resistance force.

Input Force and work1 Force • Describes by its strength, or magnitude, and

the direction in which it acts. • The standard unit for the magnitude of a

force is the Newton (N).

•An arrow can represent the direction and strength. The arrow points in the direction of the force. The longer the arrow, the greater the force’s strength.

Input Force and work1 Work • You can calculate the amount of work done

on an object by multiplying force times distance.

•This formula can be used to calculate the amount of work you do to lift a plant.•When you lift an object, the upward force must be at least equal to the object’s weight.

Input MachinesLevers•First person to explain how levers work was Archimedes, a mathematician of ancient Greece.•A level is a simple machine that makes lifting heavy objects easier.

Input Levers at Work

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.

Input Smooth Muscle A hammer acts as a lever when you pull a nail

from a board.The force exerted on the lever

The hammer changes the direction an amount of force you exert, so the nail is easier to remove.

The force exerted on the object

Input Different Classes of LeversClass 1 – The fulcrum is between the effort force and the

resistance force. always change the direction of the effort force.

Input Different Classes of LeversClass 2 – the resistance force is between the effort force

and the fulcrum.Increase force, but do not change the direction of the

effort force.

Input Different Classes of LeversClass 3 – the effort force is between the resistance force

and the fulcrum.Increase distance, but do not change the direction of the

effort force.

Input Machines in the BodyWhen you move your legs, hips, hands, or head, your

are using a lever system to perform the movement. Most of the machines in your body are levers that

consist of bones and muscles.Many of the body’s movable joints are actually

fulcrums.The joints act as pivot points for the bones. The bones act as levers, and muscles provide the force.The thigh joint, the wrist joint, the shoulder joint, the

knee joint, and the elbow joint are examples of fulcrums for third-class levers in the body.

Input Machines in the BodyThe joint at the top of your

neck is the fulcrum of a first-class lever.

The muscles in the back of your neck provide the effort force.

The resistance force is use to tilt your head back.

Input Machines in the BodyThe ball of your foot is the

fulcrum of a second-class lever.

The muscle in the calf of your leg provides the effort force.

The resistance force is used to raise your body.

Input Machines in the BodyYour elbow is the fulcrum

of a third-class lever.Your biceps muscle

provides the effort force.The resistance force is

used to lift your arm.

Finish the Front of Notes on your ownAcross Discipline: Language Arts Use you math skills to

calculate the Effort force and Resistance force for the problems on page 535

Question: Write 2 questions using your Blooms Taxonomy Card (analysis) and answer them.

Compare and contrast the 3 types of levers in the body.

Summary (Blooms): Retell in your own words what this section was about.

Answer # 1, 2, 3Guided Practice

Independent PracticeFinish # 4-7