Teaching six simple machines to middle school students

Ingram School of Engineering

Bahram Asiabanpour, Ph.D., CMfgEJaime Hernandez, Ph.D.

Vasilis Vagias, Matthew Loerwald, Thomas Wilson STELLAR II: Science and Technology for English Language Learners

Stellar summer institute, San Marcos, TX

TAKS 8th grade exam sample question

Definitions

Distance

Mass

Velocity

Acceleration

Force

Work

Distance

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

MassThe 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.

Velocity

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

AccelerationThe 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.

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)

Work

Work is the product of a force applied over a distance.

W = F x d

Understanding energy, forces, and motion Six simple machines

Inclined plane

Wedge

Screw

Levers

Wheel and axel

Pulley

Simple Machines

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?

Simple Machines

Lever

Pulley

Wheel & Axle

Wedge

Inclined Plane

Screw

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.

1- Inclined plane

• Real world example: Ramps, Roads, Steps, etc.

1- Inclined plane• In class experiment1- 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

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

2 - Lever

• Real World Example: Handles, Can Openers, Seesaws, etc.

2 - Lever• In class experimentMaterials: Ruler, pencil, and two masses

Directions: Set up materials as shown on a flat surface.

1. Use pencil as the fulcrum use spring scale where the “effort” is applied and measure force.

2. Move pencil and repeat measurement record new force.

3. Validate Fr x Lr = Fe x Le

Position 1L1=L2

Position 26L1=4L2

Recorded force

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

3 – Pulley• Real World Examples: Flag Poles,

Dumbwaiters, etc.

3 - Pulley• In Class ExperimentMaterials: 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

4 - Wheel & AxelDefinition: 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

4 – Wheel and Axel

• Real World Examples: Cars, Ferris wheels , wheelbarrows, etc.

4 – Wheel and Axel• In class experimentMaterials: Mass hanger, rope, the small car, and spring scale.

Directions:

1. Attach spring scale to rope and pull mass without the small car.

2. Place mass on small car and pull with spring scale.

3. Record results for all.

With Without

Recorded force

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.

5 - Wedge

• Real World Examples: Axes, door stops, chisels, etc.

26

Example: Cutting tool

A

B

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.

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.

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.

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

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!

Conclusion

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

Relevant videos

• Screw and the wheel (4 minutes)http://www.youtube.com/user/123peaceplease#p/u/10/v1hjiOp6FEU

• Lever (3 minutes)http://www.youtube.com/user/123peaceplease#p/u/11/Us2KfO_yrPA

• Simple machines (6 minutes)http://www.youtube.com/user/123peaceplease#p/u/13/grWIC9VsFY4

• Inclined plane (5 minutes)http://www.youtube.com/user/123peaceplease#p/u/12/wWPiY6Of6-U

• Pulleyhttp://www.youtube.com/watch?v=9T7tGosXM58&feature=related

More Examples

• http://www.mikids.com/Smachines.htm• Students project: Six simple machines (all in one)http://www.youtube.com/watch?v=l1oCpWZk8pk