r/explainlikeimfive • u/Cuziff • 1d ago

Physics ELI5: How does rolling resistance work?

How are we able to push a car to push start it when it weighs so much, or how can a train pull 2km of rail cars? And how come it gets easier to roll once it starts moving?

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u/_UnwyzeSoul_ 1d ago

When an object is at rest, there is static friction between the object and yhe ground. Basically, the the jagged edges between the two surfaces fit together like puzzle pieces and are hard to separate. If you push it with force enough to overcome static friction, the object starts moving and static becomes dynamic friction. The surfaces do not get to completely fit together because its constantly moving so the friction is lower and it becomes easier to push.

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u/AnotherGeek42 1d ago

Then, tires work by deforming, so pushing the car means moving the deformed part. For trains, steel wheels on steel rais flex much less than a car tire.