# Explain the whole bullet and train thing to me.

**URL:** https://boards.straightdope.com/t/explain-the-whole-bullet-and-train-thing-to-me/384642
**Category:** Factual Questions
**Created:** [December 18, 2006, 4:07pm UTC](https://boards.straightdope.com/t/explain-the-whole-bullet-and-train-thing-to-me/384642 "2006-12-18T16:07:35Z")
**Posts on this page:** 1
**Showing post:** 39

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### Author: ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)
#### Post date: [December 6, 2022, 6:16pm UTC](https://boards.straightdope.com/t/explain-the-whole-bullet-and-train-thing-to-me/384642/39 "2022-12-06T18:16:42Z")

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IMO an even more interesting situation is when a pebble is stuck in a tire tread.

Let’s say a car has a speed of 60 MPH and a pebble is stuck in a tire tread. When the pebble is at the 12:00 position (highest point), the pebble has a speed of 120 MPH relative to the road. When the pebble is at the 6:00 position (lowest point), the pebble has a speed of 0 MPH relative to the road. When the pebble returns to the 12:00 position, the pebble has a speed of 120 MPH relative to the road. And so on.

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