Tutorial launch
A force is a push or a pull, and we measure it in newtons (N). An object's mass is measured in kilograms (kg).
When unbalanced forces act on an object, its velocity changes. It has an acceleration, measured in meters per second squared (m/s²).
Newton's Second Law tells you how big the acceleration is: acceleration = net force ÷ mass. People often write it as F = m × a, where F is the net force.
Press Launch. The counterweight drops, and the sling yanks the pumpkin along the trough, the wooden track under the machine. The launch pauses right at the start of the swing. Use the numbers under This launch to find the net force and the acceleration for the first row of your worksheet. Then press Keep going to watch it fly, and add the distance.
Pumpkin drawn bigger than real size
What this model leaves out
- Forces are rounded to the nearest newton. Each launch pauses at a moment when subtracting the rounded numbers gives the true net force, rounded to the nearest newton.
- At the pause, the sling also pulls up on the pumpkin a little (less than 4 N), and the trough pushes up on it. Together those two forces balance the pumpkin's weight, so up and down, the forces are balanced.
- Friction uses one estimate for wood rubbing on pumpkin rind. Real friction changes with how wet, rough or bumpy the wood and the rind are.
- The arm and frame never bend, the counterweight is bolted to the arm, and the frame is fixed to the ground. Many real machines let the counterweight swing.
- The pumpkin is treated as a ball that doesn't spin, and there's no wind. Air resistance uses one rough estimate for each pumpkin shape.
- Burst limits are estimates. In a squeeze test, whole pumpkins broke at about 1,500 to 1,800 N. The limits here are set around that range, lower for thin-rinded pumpkins and higher for thick-rinded ones, and real pumpkins vary.
- Real competition trebuchets have thrown pumpkins more than 1,000 m. This machine reaches about 440 to 480 m, depending on your pumpkins.
Launch to see the forces at the start of the swing.
- Sling pull, toward the back
- Friction, toward the front
- Pumpkin's mass
- Forces up and down
- balanced
Work out the net force and the acceleration on your worksheet.
- This first launch is set for you: a Sugar Pie pumpkin, a 5,000 kg counterweight and a 35° release angle.
- The sling pulls the pumpkin toward the back, and friction from the trough pushes it toward the front. They point in opposite directions, so you subtract them to find the net force.
- After the tutorial, the Chunk-Off opens and the settings are yours.
That's the tutorial. The Chunk-Off is open.
