Teachers TryScience

This lesson will require one block to introduce the project and to explain how the physics just covered applies, then another block to have the students demonstrate their catapults, and a last block to reflect on what was learned.  Allow about three weeks from assignment to execution.

1. Your challenge is to launch a projectile at a target sixteen feet away with precision and accuracy. The projectile must also pass over a one-meter tall wall without touching it. You may use any materials to build your catapult. However, you must use materials that can normally be found around the house.  The idea of the contest is to be creative not to purchase high-tech materials.  If you have any questions pertaining to the materials you have selected, you must BRING them to your teacher for approval in writing.  In addition, there may not be any chemical or nuclear reactions used in the catapult. There may not be any feature that could be deemed as dangerous to the spectators.  No part of the catapult may burn during the contest.
2. Your catapult may use any means you can devise for launching the projectile.  You may not, however, use any electric or gas operated motors nor may you use any chemical reactions.  A catapult may use springs or elastics or steel bars to launch the projectile.  The action of firing must be reproducible.  The catapult may not self-destruct during the contest.  The spring constant (k) cannot exceed 2000 N/m.
3. Your catapult must support itself at the start. The catapult must be "loaded" and then fired.  In other words, the catapult will be put into a launch position; the ping-pong ball placed on it and then you may fire it. This could be by cutting a string, pulling a pin or any other method you devise.  Your catapult must be self-operated.  You may touch it to start the launch but you may not give it a push.
4. Your catapult must occupy a space described by 12 inches long, 12 inches wide and 12 inches high at the start of the launch.  The maximum weight of the catapult is 4 pounds.
5. Your grade on this project will be determined by the average of the best three out of four throws.  A distinguished panel of judges will determine the grade received on each throw.
6. A one-meter tall wall will be placed half way from the start line to the target on the other side of the wall.  The ball must pass over the wall without touching the wall.  The ball may not hit the ceiling.
7. Students will launch a ping-pong ball projectile.   Everyone is working under the same constraints. The distance from the catapult to the landing site will be measured.

This is the beginning of an adventure into modeling, cooperative learning, and applied science.  Each team should complete Catapult Assignment #1,  which includes:

• A listing of team members by name, physics period, and teacher
• Acknowledgment that most of the materials needed have been acquired and a model attempted.
• A labeled drawing of plans for the catapult you will be constructing
• A description of how the catapult will work; in which you mention the physics principles/laws that will be applied. 

Calculations should be done later and will show maximum height, initial force and total energy of the system.  An Experiment that measures these could be done in place of the calculations.

Your team may decide to revise your original plans along the way.  That is okay.  It is even expected.  The second homework assignment, Catapult Assignment #2, which is associated with this laboratory activity, will consist of a revised labeled diagram of plans for the catapult and a final description of how it is going to accomplish its competitive mission. The second homework assignment must also contain calculations for force applied, maximum height, initial velocity and maximum horizontal distance.  Please see Catapult Calculations Sheet. Revisions are expected to be necessary after your team conducts some trial shots.

On the final project date, we will set up the target, the wall, and test each and every catapult.  No late projects will be accepted.  You may, of course, hand in the catapult earlier. 

NOTE:   If you use a spring, the value of k must be calculated and you may be required to prove the experiment.  To calculate the value of k, you must suspend the spring from a strong bar and hang weights on the spring.  When you hang each weight on the spring, you will measure the distance it drops.  Then you will plot the Weight on the Y-axis and the Distance on the X-axis.  The k value is the slope of the resulting graph.   The k value cannot exceed 2000 N/meter.