GRADE: Fifth

CONTENT STANDARD: Physical Science

CONTENT TOPIC: Simple Machines/Technology

CONCEPT: Machines can be used to alter a force.

CONTENT OBJECTIVE: 5A1.00 To understand the effect of machines on force

INSTRUCTIONAL OBJECTIVES: The learner will:

1.01 identify the main types of machines.
1.02 relate how people use these machines to alter forces to do work.
1.03 identify the four ways machines help us.
1.04 select a situation that represents machines altering forces in each of the four ways.
1.05 construct machines that alter forces and describe how the force is altered.
1.06 know that some machines can alter a force in several ways at the same time.

I. Types of machines
II. Machines change force
III. Advantages of machines

TN COMPONENT OF SCIENCE: Unifying Concepts of Science

TN GOAL:

To enable students to acquire scientific knowledge by applying concepts, theories, principles and laws from life/environmental, physical, and earth/space science.

2.2 FORM AND FUNCTION - Form may determine the function of a material or a system, and function may alter form.

2.2a How an object functions is related to its form.

BENCHMARK: The form of a structure implies its function. The function of a structure tends to dictate its form.

2.2b Form tends to dictate function, thus an alteration of form may lead to a change in function.

BENCHMARK: Physical and biological systems are interactive. Changes of component forms may alter the function(s) of those systems.

TIME REQUIRED:

Two to three instructional periods

Old typewriter, bicycle, pencil, paper

(Bring a bicycle into the classroom and identify the parts.) Today we are going to learn about simple machines and how they can help us alter forces.

Machines are very important to man because they help to make the work easier and decrease the time it takes to do the work. All machines are classified as simple or complex. Raise your hand if you can tell me the difference between simple and complex machines. (Simple machines have only one or two parts. Complex machines combine two or more simple machines.) The principle component or part of a complex machine is a lever. What are some examples of levers? (Crowbar, seesaw, shovel, scissors, bottle opener) When we use machines, we have what we call a mechanical advantage. This means whatever amount of force we use on the machine is multiplied by the machine.

Mechanical advantage is expressed in one of two ways. The ACTUAL mechanical advantage is the number of times that a machine multiplies the effort force. The IDEAL mechanical advantage calculates the mechanical advantage without friction and weight of the lever being considered. Thus the IDEAL mechanical advantage would be larger than the ACTUAL mechanical advantage.

Actual Mechanical = Advantage

Resistance Force Effort Force

Ideal Mechanical = Advantage

Effort Arm Resistance Arm

As I hold up one of the simple machines, tell me which purpose it fulfills.
Lever (Changes amount of force)
Wheel and axle (Force is increased)

A pulley is a simple machine that may change the amount, speed, and direction of a force. It is a wheel that turns on an axle. It can be fixed or movable. The total number of support ropes of a movable pulley is always equal to the ideal mechanical advantage.

An inclined plane is a slanted surface which is used for raising objects to higher elevations. Less effort is needed with an inclined plane, because an object is moved a longer distance on a slanted surface.

A wedge is a double inclined plane. A long narrow wedge requires a small effort force to overcome a great resistance force.

A screw is a circular inclined plane. It appears to be an inclined plane wound around a center to form a cylinder. It requires a small effort force in turning to overcome a large resistance force.

Machines are used to change force. Machines change force in three ways:

1. Machines change the amount of force. When you use a bottle opener you increase the amount of force. You can't open an old-fashioned coke bottle with your bare fingers. But the opener changes the amount of force under the cap and pushes the top off.

2. Machines change the amount of speed of force. A conveyor belt is an example of this. Is a conveyor belt a simple or complex machine? (Complex) Why? (Uses two or more simple machines)

3. Machines can also change the direction of force. A pulley is an example of a machine changing the direction of force. Who can explain how a pulley changes the direction of force. (Usually changes the downward force to an upward force)

(Place a book on the edge of a table or desk. Insert about 2 centimeters of a ruler under the edge of the book. The remainder of the book should extend out beyond the table. Pull up on the end of the ruler so it raises the book.) Where is the fulcrum and effort force? (response) Now change the positions.

(Support a yardstick in the center with a string. Tie unequal weights to either side. Move weights back and forth and determine the position at which the lever is balanced.)

(Obtain two simple pulleys, a double pulley and an object of known weight. You need a meter length of string, and a ring stand which you can suspend a pulley. Suspend a single pulley, add string and weight to make a machine with a M.A. of one. Attach a string balance to the effort end of the string. Measure the force needed to raise the weight. Arrange the pulleys for the M.A. of two, and M.A. of 3. Make a drawing for each arrangement. Label the M.A. and effort force for each.)

(Tie a string to a brick or block. Then attach a spring scale to the string and weigh the brick or block. The reading on the spring scale is the force needed to lift the block straight up. Set a smooth board against a pile of books to make an inclined plane. Attach the spring scale to the string and pull the block up the plane. Pull the block at constant speed - don't jerk it. Read the scale while the block is moving. The reading on the scale gives the force used to pull the block up the inclined plane. Compare the forces needed to lift and pull the block. What is the A.M.A. of the inclined plane?)

Take out a sheet of paper and a pencil. I want you to name four of the most helpful machines to you and explain why.

Today we have learned that machine have an effect on force. I have brought an old typewriter (An old clock or other similar item could be used.) I have taken it apart. Make a list of all the simple machines that are in the old typewriter.

Teacher orally presents dysfunctional simple machines. (Example: a wedge with a blunt point, a smooth pulley, a screw with no grooves, or a square wheel) Children will discuss in groups how this change will decrease the effectiveness of each simple machine. (Each group is given one machine.) Afterwards, each group will report to the class.

(Have each student make a pulley from empty thread spools and wire clothes hangers. Cut the wire of a hanger 20 centimeters on each side of the book. Bend the ends and slip them through a spool.)

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