Trebuchet Physics

Objective:

The purpose of this unit is to learn the physics and math associated with Trebuchet Technology. In addition, students will be required to design and constructed a trebuchet to launch a clay projectile as far as possible. Students will also compete against each other in a trebuchet battle.

Background:

Complete the Trebuchet Vocabulary worksheet. Remember you will be tested on the definition to these terms. Review the definitions on the worksheet as a bell ringer exercise before taking the test.

Watch this short video, How to Build a Trebuchet (Mythbusters)

Launch the link to experiment with different designs for a simple virtual trebuchet --->

The success of your trebuchet will depend on the following design characteristics, choose well:

1. Fulcrum location, for example the ratio between the long section (sling) and the short section (counterweight) of the throwing arm. (L2)/(L1) and ((L2 + L3)/(L1 + L4)

2. The length of the sling in relationship to the length of the long section of the throwing arm. L3/L2

3. The mass of the counterweight. weight of m1

4. The ratio of the counterweight mass to the projectile mass. m1/m2

5. The motion of the counterweight is important

6. The distance the counterweight hangs from the end of the throwing arm is important. L4

7. The length of the sling L3

8. Overall construction quality.

9. Operator skill and aim.

To learn more about trebuchet physics, launch Virtual Trebuchet to learn techniques to increase trebuchet launch distance.

• ONLY adjust the Release Angle, determine the optimum angle of release.

• Refresh the screen.

• ONLY adjust the Mass of Weight, determine the optimum mass of the counterweight.

• Refresh the screen.

• ONLY adjust the Length of the Long Arm and the Length of the Short Arm. Determine the ratio for launching a projectile the furthest.

• Experiment with the settings, it's important to design and build a projectile to launch a cow as far and as accurately as possible.

• Turn on your call light and show your teacher your best launch. You must throw a cow at least 300' before beginning work on your trebuchet.

Safety (Students MUST score 100% on the following tests to work in the lab):

• • Launch the ABC of Hand Tool Safety 1 & ABC of Hand Tool 2 videos, complete the Hand Tool Safety Test worksheet and take the ABC of Hand Tool Safety Test

  • Launch the Power and Hand Tool Safety video and complete the Portable Power Tool Safety Test worksheet and take the Power and Hand Tool Safety Test

• Launch the Drill Press Safety video and complete the Drill Press Safety Test worksheet and take the Drill Press Safety Test

• Launch the Band Saw Safety video and complete the Band Saw Safety Test worksheet and take the Band Saw Safety Test

• To prevent injury, learn the safety rules presented in the videos. Also, you will be tested on these competencies often in this class.

Procedures:

Click on each image below for a more detailed view

Get template and 12" x 5" piece of wood

Shape and smooth tip of throwing arm and supports using a hand file or rasp, table vise and 80 grit sandpaper

• • • • • • • • • Using files and rasps video (basic)

                • Files, rasps and sandpaper (advanced)

Use band saw to cut slot for counterweight

Use 80 grit sand paper to remove paper template and glue from face of stock

Assemble throwing arm using 3" machine screw and three hex nuts

Troubleshooting:

• • Check the length of the sling arm. It is crucial.

  • Check the length of the firing pin.

  • Check the size and shape of the poach if your projectile is launching too late or too early in the motion of the throwing arm.

  • Check the number of weights

  • Calculate the ratio between the load arm and the effort arm of the throwing arm, it is crucial.

  • Make sure your counterweight isn't hitting the throwing arms during launches.

  • In summary, there are plenty of design issues that command your attention. The design issues cited above are just a small sampling of the problems you might encounter in troubleshooting your compound machine. Use your problem solving skills to build and operate the trebuchet with the greatest range.

Tips:

According to Donald B. Siano, in his analysis of trebuchet physics (Trebuchet Mechanics, March 28, 2001), the optimal release position and design, based on his definition of "range efficiency" is such that:

• The initial release position is such that the beam on the counterweight side makes an angle of 45° with the vertical.

• The length of the long arm of the beam (on the payload side) is 3.75 times the length of the short arm of the beam (on the counterweight side).

• The length of the sling is equal to the length of the long arm of the beam (on the payload side).

Furthermore, he recommends using a counterweight that has a mass 100 times greater than the mass of the payload. However, it is certainly possible to achieve a good design with a much lighter counterweight than this.

Good Luck!

Assessments:

• Band Saw Test Review (100 points)

• Virtual Trebuchet Simulation (100)

• Trebuchet Vocabulary (100)

• Trebuchet Construction and Test (500)

• Trebuchet Physics Test (100)

Enrichments:

• When you've finished your trebuchet project, turn on your call light and your instructor will issue you a goal post and tape measure to record the longest "field goal" you can make with your project.

• Students who successfully construct and test the trebuchet will get a Catapult project to construct and test.

• After completing your catapult, record your accuracy and distance attempting "field goals" using a goal post and tape measure.

Links:

• Trebuchet Simulation

• Virtual Trebuchet

• Trebuchet Physics