explain xkcd - User contributions [en]

3174: Bridge Clearance

2025-11-28T21:47:07Z

Frigidus08: added explanation. change this in any way if needed

{{comic
| number = 3174
| date = November 28, 2025
| title = Bridge Clearance
| image = bridge_clearance_2x.png
| imagesize = 450x233px
| noexpand = true
| titletext = A lot of the highway department's budget goes to adjusting the sign whenever the moon passes directly overhead.
}}

==Explanation==
{{incomplete|This page was created recently. Don't remove this notice too soon.}}
Bridges will often have signs indicating the height of the bridge, primarily to indicate to taller vehicles the potential hazard of driving under them. In this comic, there is a bridge with one of these signs, indicating a clearance of 10 feet and 6 inches, which is a normal clearance for a bridge to have. To its right, there's a sign which says "no bridge", indicating a clearance of 46 billion light years. This sign indicates a clearance approximately equal to the radius of the observable universe.
The title text references the fact that when the moon passes over the sign, the clearance would be reduced to the distance between Earth and the moon, as any vehicle driving there would need to be shorter, otherwise it would crash into the moon. Both of these signs ignore the fact that vehicles cannot be large enough that either of these clearances would be something necessary to account for while driving.
==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}

{{comic discussion}}<noinclude>

3138: Dimensional Lumber Tape Measure

2025-09-06T01:11:56Z

Frigidus08:

{{comic
| number = 3138
| date = September 5, 2025
| title = Dimensional Lumber Tape Measure
| image = dimensional_lumber_tape_measure_2x.png
| imagesize = 532x478px
| noexpand = true
| titletext = A person with two watches is never sure what time it is, especially if I got them one of the watches.
}}

==Explanation==
{{incomplete|This page was created recently. Don't remove this notice too soon.}}
A 2x4 is a type of dimensional lumber, meaning it is cut to a specified length. In the case of a 2x4, despite specifying dimensions of 2 inches by 4 inches, its actual dimensions are 1.5 inches by 3.5 inches. The Dimensional Lumber Tape Measure "fixes" this inaccuracy by changing the length of its indicated inches so that a 2x4 is measured as 2 inches by 4 inches.
==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}

{{comic discussion}}<noinclude>

3086: Globe Safety

2025-05-08T04:46:30Z

Frigidus08: added to expanation (my first edit)

{{comic
| number = 3086
| date = May 7, 2025
| title = Globe Safety
| image = globe_safety_2x.png
| imagesize = 255x448px
| noexpand = true
| titletext = Frankly, given their extreme gravitational fields and general instability, even 12-inch globes should probably be banned.
}}

==Explanation==
{{incomplete|This page was created recently. Don't remove this notice too soon.}}
A Schwarzschild radius of a given object is the radius of the event horizon of a black hole with the mass of that object. Since the Schwarzschild radius of the earth is about 0.7 inches, this hypothetical Globe Safety avoids creating black holes by imposing a limit on the size of globes, stating that they should not be smaller than 4 inches in diameter (despite the fact that a 4-inch wide Earth would still have significant gravitational influence).
The title-text takes this situation further, by suggesting the 12-inch globes should also be banned, due to their extreme density and gravitational field.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}

{{comic discussion}}<noinclude>