Activity 3C

C&I 335

Summer 1998

 
Jan Hari
8th Science Teacher
Science Coordinator
Urbana Middle School/District #116
Urbana, Illinois


Mini Lesson Plan

 

Background/Previous Experience

The eighth grade science students at Urbana Middle School study simple machines in a very practical way by building a number of devices. They build catapults and mousetrap cars. When they build the mousetrap cars, they learn with varying degrees of quickness that the size of the wheels in combination with how much and how long the force is applied makes a big difference in how far the car will go. A more difficult area of problem-solving is making the car go straight. It is common for students not to have the axle in the center of the wheel. They soon learn to recognize what they call the lopsided "hoopy" motion. Students study simple machines: levers, pulleys,wheels and axles, gears, inclined planes, but we rarely study cams. Cams are rarely studied even though they are a very common solution in ordinary life to change rotary motion into linear motion. Cams are very like the uneven wheels on the mousetrap car that push against the ground. The reason they are not studied is because they are difficult to construct or operate with common classroom materials. This applet does a wonderful job of animating a cam, giving students a chance to visualize one, and allowing students to analyze what happens. The students can watch it over and over again with the three graphs side by side to understand how it works.

Objectives:

Materials:

Time: One 40 minute class to download and to analyze the motion.

Procedure:

To save time students may download from Mrs. Hari's electronic page.

Students should spend most of their time analyzing how a cam works and making sure they are answering the questions suggested using either HomePage 3.0 or B.B.Edit Lite.

Students should be reminded of the parameter chart below the animation.

Questions:

  1. Who designed this animated cam?
  2. Where is the person from?
  3. How far is the red roller lifted (follower lift)?
  4. Notice carefully how fast the red roller moves up and down.
  5. How does the the acceleration change as the red wheel goes to the top of the yellow pear shaped wheel?
  6. What is the velocity at the top of the pear shaped wheel?
  7. What is the velocity at the bottom of the pear shaped wheel?
  8. Do you see a change in acceleration?
  9. What does the graph say about acceleration?
  10. What happens to the blue shaft as the red and yellow wheels go around?
  11. What common every day items have you seen this motion in?
  12. How would you rate this applet? What features would you like to see included?
You need Netscape 2.0+ or Internet Explorer to view this applet.
(Applet Version 1.0)
Note: If Applet is not visible after loading all files, click Reload Button on your Browser.
You can down load zip file (size~16k) of this Applet
Comments, feedback and suggestions are encouraged.
Please send mail to
soh64@poboxes.com

CAM FOLLOWER MOTION SIMULATION

This Applet demonstrates the Real time simulation of Cam Follower mechanism. The parameters used for this combination are given by

Cam

Straight Flank

Follower

Roller

Base Circle Radius

1 inches

Nose Radius

1/2 inches

Center Distance

1.5 inches

Follower Radius

1/2 inches

Follower Maximum Lift

1 inches

Cam Speed

60 rpm(Maximum, CPU dependent)

Units of Lift,Velocity, Acceleration

in, ft/sec, ft/sec^2

Students should be reminded of their responsibilities to give credit even though this is a free applet. Students will also notice that the author of this applet is not from the United States and we can talk about programming as a career or hobby without borders. Students can describe what they features they wish this applet might have such as the ability to change the sizes of the two wheels.

Extensions:

Students in subsequent lessons will use the computer and the Internet to add to their html library of simple machines. They may use a variety of resources to illustrate or give examples of simple machines explaining their mechanical advantage in text that accompanies the photograph, animated drawing, film clip, scanning a picture, or link to a cartoon site that illustrates a certain machine. Students can have appropriate musical accompaniment with examples of their machines. The open format allows for a wide variety of learning styles and abilities.

In the past when we have done the simple machines poster, the students have surprised us with their originality and creativity as well as their ability to explain a science concept. I am excited about finding the animated cam and looking forward to using technology to see them develop original simple machine html libraries.

Simple machines are also taught at the fifth grade level. Students might be able to go to Wiley Elementary, one of the elementary schools within walking distance, and share their html library with fifth graders or they could share their findings by e-mail if the libraries were on the server.

Return to ePortfolio