About this experiment
Pull the handles on either side of a toy cart. Balance the forces, make one side stronger and compare how mass and track resistance change the resulting motion.
Learning goals
- Find the direction and magnitude of a net force.
- Predict when a balanced cart stays at rest.
- Compare acceleration for the same force applied to different masses.
How to use it
- 1Run the default unequal forces and record which way the cart moves.
- 2Balance the handles and repeat from rest.
- 3Reverse the forces and compare the signed displacement.
- 4Add enough dry resistance to hold the cart, then increase one force until it moves.
The model
Assumptions
- Every parameter change prepares a new run from rest. The forces are collinear and stay constant during a run.
- Dry resistance can balance an applied force up to the chosen limit. Once sliding, its magnitude equals that limit.
- The model omits rolling inertia, air resistance and track-end collisions. The scene uses a fixed distance scale and follows the cart near the viewing edge.
Try this in class
- Q1What happens when equal forces pull in opposite directions?
- Q2How can a nonzero applied force coexist with zero net force?
Frequently asked questions
Why does the cart sometimes stay still with unequal handles?
Static resistance balances their difference when it is below the chosen resistance limit.
Do balanced forces always imply zero speed?
They imply zero acceleration. This activity resets to rest for each run; the inertia experiment separately demonstrates balanced forces with nonzero speed.