The problem "Congratulations! You just bought a brand new iron rod ..."

The problem is "Congratulations! You just bought a brand new iron rod that has a length of 1 lightyear. Now, suppose you pushed one end of the rod. About how much time will pass before the other end moves?"

This ignores the fact that the far end of the rod can move immediately to the "side." That is, the rod is apparently assumed indirectly to be rigid to the sides. In fact, the rod would twist/stretch/shorten differently at different spots etc. So the answer is "immediately."

#Mechanics

Note by Kelly Waters
5 years, 8 months ago

1 vote

  Easy Math Editor

This discussion board is a place to discuss our Daily Challenges and the math and science related to those challenges. Explanations are more than just a solution — they should explain the steps and thinking strategies that you used to obtain the solution. Comments should further the discussion of math and science.

When posting on Brilliant:

  • Use the emojis to react to an explanation, whether you're congratulating a job well done , or just really confused .
  • Ask specific questions about the challenge or the steps in somebody's explanation. Well-posed questions can add a lot to the discussion, but posting "I don't understand!" doesn't help anyone.
  • Try to contribute something new to the discussion, whether it is an extension, generalization or other idea related to the challenge.
  • Stay on topic — we're all here to learn more about math and science, not to hear about your favorite get-rich-quick scheme or current world events.

MarkdownAppears as
*italics* or _italics_ italics
**bold** or __bold__ bold

- bulleted
- list
  • bulleted
  • list

1. numbered
2. list
  1. numbered
  2. list
Note: you must add a full line of space before and after lists for them to show up correctly
paragraph 1

paragraph 2

paragraph 1

paragraph 2

[example link](https://brilliant.org)example link
> This is a quote
This is a quote
    # I indented these lines
    # 4 spaces, and now they show
    # up as a code block.

    print "hello world"
# I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
MathAppears as
Remember to wrap math in \( ... \) or \[ ... \] to ensure proper formatting.
2 \times 3 2×3 2 \times 3
2^{34} 234 2^{34}
a_{i-1} ai−1 a_{i-1}
\frac{2}{3} 23 \frac{2}{3}
\sqrt{2} 2 \sqrt{2}
\sum_{i=1}^3 ∑i=13 \sum_{i=1}^3
\sin \theta sin⁡θ \sin \theta
\boxed{123} 123 \boxed{123}

Comments

Hi Kelly, it is best to join the solution discussion of the problem, as opposed to writing up a note about it. Then everyone can see the response to your concerns.

Calvin Lin Staff - 5 years, 8 months ago

Don't you mean, "Probably never"? If we had a real iron rod a light year long, it would be so extremely flexible because of its slenderness, we'd have a hard time distinguishing the one disturbance at the other end that's actually due to the rod being pushed at the base end. But physics is often like that. First, we consider a mathematically ideal rod with infinite stiffness, then we consider a slightly less ideal rod where it's only longitudinally flexible, then we start getting into real rods which have more in common with cooked spaghetti strands. String theory, anyone?

Michael Mendrin - 5 years, 8 months ago

Infinitely stiff was not assumed.

Kelly Waters - 5 years, 8 months ago

I mean to point out that when analyzing a physics situation, we often make some simplifying assumptions, such as assuming only longitudinal flexibility. In other words, you're assuming a too-realistic iron rod, in which case we can probably forget about trying to talk about what happens at the other end of an iron rod a light year long!

Michael Mendrin - 5 years, 8 months ago

there is space between molecules of matter.

yogesh mahavaria - 5 years, 8 months ago
×

Problem Loading...

Note Loading...

Set Loading...