The washing machine: why it “walks”
Two machines spin a drum with laundry. In the left one the load is spread evenly and the machine stays, in the right one it is in a single lump and the machine creeps across the floor.
Drag to orbit the scene, scroll to zoom. Press “Run”.
What the experiment shows
The lump of laundry goes round with the drum and pulls it outward. The force points one way, then the other, and the cabinet shakes and shifts. An evenly spread load balances itself.
How to run it
- Press “Run”: the drums spin up.
- Compare the cabinets: which one stays and which one moves away?
- Select the right machine’s motor and halve its speed — how does the shaking change?
Questions to discuss
- Why is the shaking force called centrifugal and how does it depend on speed?
- How do modern machines fight imbalance?
The science
A lump of mass m at distance r from the axis spinning at angular speed ω makes a rotating force F = m·r·ω². Here that is 2 kg · 0.2 m · 22² ≈ 190 N. When the force exceeds the friction between the cabinet and the floor, the machine creeps. The force grows with the square of the speed, so imbalance is most dangerous at high rpm. An evenly spread load splits the mass into two opposite spots: the forces cancel.
Try it at home
Stick a ball of modelling clay near the edge of a jar lid and spin it on a table, then put two balls opposite each other. Compare how the lid shakes.
What to change in the editor
- Make the cabinet heavier (80 kg) — will the machine stop creeping?
- Put the lump closer to the axis.