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** Teaching six simple machines to middle school students**

Ingram School of Engineering Bahram Asiabanpour, Ph.D., CMfgE Jaime Hernandez, Ph.D. Vasilis Vagias, Matthew Loerwald, Thomas Wilson STELLAR II: Science and Technology for English Language Learners Stellar summer institute, San Marcos, TX

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**TAKS 8th grade exam sample question**

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Definitions Distance Mass Velocity Acceleration Force Work

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Distance An increment that represents a finite change in position. How far apart two objects are.

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Mass The mass of an object is a fundamental property of the object; a numerical measure of its inertia; a fundamental measure of the amount of matter in the object. Mass can be measured in many different ways and can appear abstract. SI units are recommended to establish comfort.

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Velocity Velocity is concerned with the change in position with respect to a change in time.

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**Acceleration The rate of change of the velocity of a moving body**

If you study a system and observe different velocities then an acceleration (negative or positive) has taken place.

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**Force Force is the product of Mass and Acceleration F = M x A**

Measured in Newtons, a well known force seen daily is lbs (pounds) and is the product of an individuals mass multiplied by 32 ft/s^2(acceleration due to gravity)

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**Work Work is the product of a force applied over a distance. W = F x d**

Half the work of the first one to move the second.

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**Understanding energy, forces, and motion Six simple machines**

Inclined plane Wedge Screw Levers Wheel and axel Pulley

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**Simple Machines Simple Machines Lever Pulley Wheel & Axle Wedge**

Inclined Plane Screw From these machines all work can be made easier in terms of force exerted at the cost of the distance moved. There are really only three simple machines the other three are just variations. Can you guess which three are they?

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1- Inclined plane Definition: It is a flat surface whose endpoints are at different heights. By moving an object up an inclined plane rather than completely vertical, the amount of force required is reduced, at the expense of increasing the distance the object must travel.

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1- Inclined plane Real world example: Ramps, Roads, Steps, etc.

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**1- Inclined plane In class experiment**

1- Set up a plane as shown in below picture with 30 degrees angle and connect a load. 2- Attached the spring scale to the other end and pull the load with it and read the scale number. 3- Change the angle to 60 degrees and compare the new scale reading with the previous one. 30 degrees 60 degrees Recorded force

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2 - Lever Definition: A long rod or stick can be placed on a point above ground known as a fulcrum to lift an object that requires a large force with a much smaller input force. There are first, second and third class Levers Fr x Lr = Fe x Le

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2 - Lever Real World Example: Handles, Can Openers, Seesaws, etc.

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**2 - Lever In class experiment Materials: Ruler, pencil, and two masses**

Directions: Set up materials as shown on a flat surface. Use pencil as the fulcrum use spring scale where the “effort” is applied and measure force. Move pencil and repeat measurement record new force. Validate Fr x Lr = Fe x Le Position 1 L1=L2 Position 2 6L1=4L2 Recorded force

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3 - Pulley Definition: A simple machine consisting essentially of a wheel with a grooved rim in which a pulled rope or chain can run to change the direction of the pull and thereby lift a load

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**3 – Pulley Real World Examples: Flag Poles, Dumbwaiters, etc.**

Part I – Setting Up Each group needs a meter stick, string, mass hanger, spring balance, mass set, two single pulleys, and two double pulleys.Set up each pulley system (A through E) as shown on the first page of the lab packet. Part II – Using the Pulleys Measure and record the mass to be lifted by each pulley system.Use the spring scale to lift the mass at a constant speed. Record the force required to lift.Remove the spring scale and pull the free end of the string 10 cm. Measure and record the distance the mass moves after pulling the string. Repeat these steps for all five pulley systems, A through E. Part III – Analyzing the Data Calculate the weight of the mass. Calculate the mechanical advantage of each pulley system. Calculate the work done while pulling on the string (work input) for each pulley system. Calculate the work done to move the weight (work output) for each pulley system. Part IV – Wrap Up (25 points total) Create a table that includes data for each pulley system showing the following: number of pulleys, mass, weight, distance mass moved, lifting force, distance pulled, work input, work output, percent error of work done, calculated mechanical advantage, number of support strings, and percent error of mechanical advantage. (20 points total)Answer the following questions. Ø What is the relationship between the number of supporting strings and the mechanical advantage of each pulley system? (1 point)Ø When calculating mechanical advantage, why can you count a section of rope you are pulling up on, but not a section you are pulling down on? (2 points)Ø Why would someone want to use a single fixed pulley? (2 points)

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**3 - Pulley In Class Experiment**

Materials: Two pulleys, rope or string, mass hangers, and spring scale. Directions: 1. Set up pulleys as shown in picture with one suspended above ground. 2. Loop rope through second pulley and attach mass hanger to the hook on the second pulley (lower pulley). 3. Use the spring scale to measure the force picking the load up by itself and again using the pulley apparatus. Without pulley With pulley Recorded force

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4 - Wheel & Axel Definition: a wheel and axel is a simple machine consisting of a large wheel rigidly secured to a smaller wheel or shaft, called an axle. When either the wheel or axle turns, the other part also turns. One full revolution of either part causes one full revolution of the other part. S1 X D1 = S2 X D2 where, S1 = Input Speed S2 = Output Speed D1 = Axle Diameter D2 = Wheel Diameter

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4 – Wheel and Axel Real World Examples: Cars, Ferris wheels , wheelbarrows, etc.

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**4 – Wheel and Axel In class experiment**

Materials: Mass hanger, rope, the small car, and spring scale. Directions: Attach spring scale to rope and pull mass without the small car. Place mass on small car and pull with spring scale. Record results for all. With Without Recorded force

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5 - Wedge A wedge is simply an inclined plane turned on its side. It follows the same rules as Inclined planes and can be thought of as such. Wedges are used as either separating or holding devices.

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5 - Wedge Real World Examples: Axes, door stops, chisels, etc.

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Example: Cutting tool A B 26

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6 - Screw A screw is simply a spiraled inclined plane. A screw can be used to move objects side to side or up and down with ease.

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Example Assume that you place a ruler parallel to a screw and count 10 threads in a distance of one inch. The pitch of the screw would be 1/10. Since there are 10 threads per inch of screw, the distance between two adjacent screw threads is 1/10 of an inch. Also, remember that one complete revolution of a screw will move the screw into an object a distance equal to the pitch of the screw. Therefore, one complete revolution will move a screw with 1/10 pitch a distance of 1/10 of an inch into an object.

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**6- Screw Real World Examples, Screws and motors**

In actual applications, the screw is often turned by another simple machine such as a lever or a wheel and axle. In this case, the total mechanical advantage is equal to the circumference of the simple machine to which the effort force is applied divided by the pitch of the screw.

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**6 – Screw: In class experiment**

Use a screw with 12 threads per inch is turned by a screwdriver having a handle with a diameter of 1 inch. The mechanical advantage would be calculated as follows: 1- Determine the pitch of the screw: Pitch = 1/12 = .083 2- Determine the circumference of the handle of the screwdriver... Circumference = 3.14 x diameter = 3.14 x 1 = 3.14 inches 3- Insert the values obtained into the formula and solve the equation: Mechanical Advantage = Circumference/Pitch = 3.14 inches/0.083 = 37.83

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**Applications in Real World**

The union of simple machines into complex machines sparked the industrial era and led to the technological boom we now live in. They are simple but highly effective machines!

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Conclusion When confronted with a cumbersome task incorporate a simple machine to take the “load” off

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**Relevant videos Screw and the wheel (4 minutes) Lever (3 minutes)**

Lever (3 minutes) Simple machines (6 minutes) Inclined plane (5 minutes) Pulley

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**More Examples http://www.mikids.com/Smachines.htm**

Students project: Six simple machines (all in one)

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