As a basic model of a trebuchet arm we will simply pin a rectangle to the background. There are several ways to attach the weight and to hold the ball (100g) in place. The arm angle can be seen in Windows | Properties.
Get the apparatus to throw
For the following graphs first establish a base configuration. That is, find a combination of pivot placement, arm angle, and mass that will actually throw the ball forward. You will need some kind of holder to keep the ball from rolling off.
Some parameters you can try if you like:
Ball mass 100g; Counterweight mass 4000g; arm length 80 cm; d2 > d1; start the arm at an angle, not horizontal; the holder cannot be too tall or it impedes the ball. The counterweight can be fixed to the arm or hung vertically on a rope.
After you get a model that actually throws the ball, start the following:
(Make sure everything is labeled including titles, scales, and units. See the Graphing data guide. )
Graph I: Varying mass - everything else fixed
Vary the mass of the counterweight. Use at least 6 points. Indicate your arm length and pivot ratio in your graph title. For example, if your total arm length is 80cm and your pivot is 20cm from the end, your pivot ratio is 60/20 = 3:1. Plot a graph of counterweight mass (horizontal axis) vs.horizontal distance thrown (vertical axis).
Graph II: Varying arm length
Vary the length of the throwing arm (longer, shorter, or both) with everything else fixed. Keep the ratio d2/d1 fixed. For example, if your pivot ratio is 3:1 and you change your arm length to 100cm, then a pivot ratio of 3:1 is 75:25. Use at least 6 points. Indicate your fixed parameters pivot ratio and mass, in the title. Plot a graph of arm length (horizontal axis) vs.horizontal distance thrown (vertical axis).
Graph III: Varying pivot ratio
Vary the pivot ratio d2/d1.Keep all other parameters fixed. Use at least 6 points.
For example, if your arm is 80 cm long d2 = 50cm and d1 = 30 cm, then your pivot ratio is 50/30 = 1.67:1. You can make your arm length longer, shorter, or both. Indicate your fixed mass and arm length in the title. Plot a graph of pivot ratio (horizontal axis) vs.horizontal distance thrown (vertical axis).
Graph IV: mass fixed vs.wheels of varying sizes - everything else fixed as indicated in your title. Build a stand to hold the arm and attach wheels to the base. Plot a graph of showing the distance thrown without wheels, then with at least 3 different sizes of wheels.
If your model crashes or freezes up try the following:
Change the accuracy to fixed - at least 50 steps/second.
If that doesn't help try this:
Shut down and restart Windows. Restart WM and create a very simple model, for example a circle bouncing on an anchored rectangle; run it to make sure it doesn't crash. Then reload your model and see if it will run.
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