Lever: Balancing Torques
1 · Predict
A lever is pinned at its exact center, with a downward push applied at each end, the same distance from the pivot. If one side pushes harder than the other, does the lever tip toward the stronger push, toward the weaker push, or stay balanced no matter what?
- It tips toward the stronger push
- It stays balanced no matter the forces
- It tips toward the weaker push
2 · Set Up
- Open the Lever preset. A rigid beam is pinned at its center; a 50 N downward force is applied 2 m from the pivot on each end.
- Click the left force arrow on the beam and note its strength in the Inspector, then click the right force arrow and do the same.
- For each row below, set the left and right force strengths in the Inspector to match, run the simulation, select the beam, and read the τ = r × F torque value from the Math panel.
3 · Collect Data
| Left Force (N) | Right Force (N) | Net Torque (from sim) (N·m) | τ = r × F (calculated) (N·m) |
|---|---|---|---|
| 50 | 50 | ||
| 50 | 80 | ||
| 70 | 40 |
Plot the force difference (Right Force − Left Force) on the x-axis against the net torque you measured on the y-axis. What does the slope represent, and where does the line cross zero?
4 · Analyze
- For each row, calculate 2 m × (Right Force − Left Force) by hand. Compare it to the net torque you read from the sim's Math panel. Do they match?
- In row 1 the two forces are equal and the lever stays level. What does that tell you about how forces and arm lengths must relate for any lever to balance?
5 · Extend
- Real levers — like a seesaw with two riders of different weight — often need unequal arm lengths, not unequal forces, to balance. If the right side's force stayed at 50 N but its distance from the pivot doubled to 4 m, what force on the left arm (still at 2 m) would be needed to balance it?
- A wrench, a bottle opener, and a pair of scissors are all levers. Pick one and identify its pivot, its applied force, and the load it moves — then explain why a longer handle makes it easier to use.
The Physics Behind This Experiment
Torque
Torque is the turning effect of a force about a pivot: τ = r × F, where r is the distance from the pivot to where the force acts. A lever balances when the torques from both sides cancel — equal forces at equal distances, or unequal forces at inversely proportional distances.