explain xkcd - User contributions [en]

3094: Mass Spec

2026-05-16T04:28:07Z

2001:4450:81E7:1E00:E160:C57F:6F73:2376:

{{comic
| number = 3094
| date = May 26, 2025
| title = Mass Spec
| image = foucault_pendulum.png
| imagesize = 407x253px
| noexpand = true
| titletext = Patients at least found it to be an improvement over Millikan's incredibly messy and unpleasant oil drop suspension procedure.
}}

==Explanation==
The domestic bathroom scale (initially a form of {{w|spring scale}}) was only introduced to US customers in the early 1920s. Although means to ascertain the weight of the human body existed before the 1920s, they were not in common use and were not thought necessary in routine physical and medical examinations. The joke in this comic arises from the claim that, before the invention of the "modern" bathroom scale, human body weights needed to be obtained, not by the earlier, less convenient, forms of scale technology which were actually used, but by absurd, Rube Goldberg-esque, implementations of {{w|mass spectrometry}}.

Mass spectrometry, a late 19th-century invention (thus, available only a few decades earlier than the bathroom scale), was developed to obtain the masses of atomic particles by ascertaining their mass-to-charge ratios. The basic steps, as represented in the comic, are ionization of the mass (rubbing the scalp with the balloon), separating the resulting particles on the basis of their mass-to-charge ratio by firing them through a magnetic field (jumping past the magnet), and observing the resulting amount of path deflection on a detector (the target). Since the ionization procedure for ''bona fide'' mass-spectrometry assays involves turning the mass to be analyzed into a gas, the method would quickly be recognized as unsuited for obtaining human body weights, especially over the course of a dieting program, and become unpopular. There are other ionization techniques to transfer larger compounds intact into the gas phase, but a human body would be way too heavy to be analyzable by this technique.

The title text compares the mass-spectrometry-based method for obtaining human body weights with the method based on the {{w|Oil drop experiment|Milliken–Fletcher procedure}}, also available only a few years prior to bathroom scales, in which the mass to be analyzed takes the form of atomized oil droplets that are ionized by X-rays. Neither is suited for weight measurements over time scales of any length, but the cleanup procedures for a human body converted into ionized gas are certainly less onerous than those for a similar mass converted into an oil spray. The original procedure was intended to determine the mass of an electron, based on the known mass/density of the oil droplets. The title text seems to imply the converse, determining the mass/density of a person based on the (now) known mass of an electron.

==Transcript==

:[Ponytail, wearing a lab coat, is giving a balloon to Cueball. Behind Cueball, there is a ramp on the ground, a magnet hanging from the ceiling and a target on a poster on the wall.]
:Ponytail: Rub this balloon against your head, then go jump past that magnet toward the target on the wall.

:[Caption below the panel:]
:Before the bathroom scale was invented, the only way to weigh people was mass spectrometry.

==Trivia==
In the comic, Randall uses the correct term "mass spectro'''metry'''". The term "mass spectro'''scopy'''" was used in the beginnings of the technique but is not used anymore. Today, a spectroscopy method entails the interaction of matter with electromagnetic radiation (e.g. IR light — as in IR spectroscopy or radio waves — as in NMR spectroscopy, nuclear magnetic resonance spectroscopy). In the case of mass spectrometry, this is not the case, as ions are manipulated or interacting with static electric and magnetic fields and thereby the mass-to-charge ratio is determined. Both "spectrometry" and "spectroscopy" allude to a "spectrum" of possible results that can be used to quantify and qualify any inputs being measured, and a distribution of molecular weights ''can'' be usefully represented in a rainbow-like visual, but doesn't bear any direct relation with the electromagnetic spectrum, hence the technical name difference. People "in the trade" often abbreviate it as "mass spec", which could stand for either term.

{{comic discussion}}<noinclude>
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]
[[Category:Physics]]

3097: Bridge Types

2026-05-16T04:26:23Z

2001:4450:81E7:1E00:E160:C57F:6F73:2376: /* Explanation */

{{comic
| number = 3097
| date = June 2, 2025
| title = Bridge Types
| image = bridge_types_2x.png
| imagesize = 740x581px
| noexpand = true
| titletext = Pontoon bridges are just linear open-sided waterbeds.
}}

==Explanation==
This comic shows, in a four-by-four grid of images, a series of bridge types. As with [[1714: Volcano Types]], [[1874: Geologic Faults]] and [[3182: Telescope Types]], the comic starts off with real bridge types, and then swiftly proceeds to make things up for absurdity. That said, real-life examples of some of the joke bridges exist, as shown in the table below. The joke lies in the progression of bridge types from the simple and straightforward to the complex and ridiculous.

{| class="wikitable sortable"
! Name given
! style="width:7em;"| Status
! Type
! Explanation
|-
! Plank
| {{Yes|Real}}
|{{w|Beam bridge}}
|A straightforward piece of solid material (in this case, made of solid wood, but there are {{w|Clapper bridge|other materials}}) is the most basic form of bridge, and generally the easiest to construct, but also the weakest. Consequently, such bridges are only suitable for small spans and light weights (such as a footbridge over a stream).
|-
! Rope
| {{Yes|Real}}
|{{w|Simple suspension bridge}}
|Rope bridges consist of several lengths of rope anchored on both sides of the span. Typically, one or more ropes will be intended to support the crossing load (possibly with boards or some other walkway between them), and additional ropes will act as handrails, reducing the risk of falling. These are typically only intended for foot traffic, due to their light construction and lack of rigidity. Because of the simple materials and relative ease of construction, they're often used as improvised bridges. However, a ridiculous design for this bridge type was explored in [[3048: Suspension Bridge]], in which the rope functions as a road.
|-
! Truss
| {{Yes|Real}}
|{{w|Truss bridge}}
|A truss is a common type of framework consisting of supports connected in a series of triangles which provide support for a load. This design provides significant strength and rigidity with minimal material and weight. A truss bridge can either have the truss above the bridge platform (as in the drawing) or underneath it (also known as a deck truss). This is the first bridge type on this list which is commonly used for vehicle traffic.
|-
! Trestle
| {{Yes|Real}}
|{{w|Trestle bridge}}
|A trestle bridge is held up by supports reaching all the way to the ground beneath. Typically at least some of the supports will slope outward to give a larger base of support. Once common for railroads, these are less popular nowadays, but are still seen in certain areas and applications.
|-
! Arch
| {{Yes|Real}}
|{{w|Arch bridge}}
|Arches are one of the oldest kinds of bridges for carrying significant loads. They can be made out of rock or metal. Each span consists of an arch resting on supports. Simple arch bridges rest on both sides of a river or other gap, but longer bridges (as in the drawing) will have intermediate pillars to support multiple arches. The arches distribute the load, allowing a relatively small number of pillars to support weight across the entire deck of the bridge.
|-
! Suspended Arch
| {{Yes|Real}}
|{{w|Through-arch bridge}}, possibly {{w|Tied-arch bridge}}
|A through arch bridge uses a similar concept as an arch bridge, but the deck is entirely or partially suspended below the top of the arch (in this case fully suspended, at the bottom of the arch). The tie of a tied arch bridge refers to using the deck as a tension member to restrain the horizontal spreading of the arch; without a tie, the arch's foundation must resist that horizontal loading. From the picture, it is not clear whether the deck is acting as a tie. Such bridges may use a single arch (as in the drawing) or multiple arches in succession.
|-
! Draw
| {{Yes|Real}}
|Drawbridge (more precisely a fixed-trunnion {{w|Bascule_bridge|bascule bridge}})
|Drawbridges are used to allow ships to pass through obstacles like bridges. They use various methods to raise one or multiple sections of the bridge to create enough height clearance for vessels to pass through, in this case using a cable to rotate the bridge about a pivot point (trunnion).
|-
! Suspension
| {{Yes|Real}}
|{{w|Suspension bridge}}
|A suspension bridge suspends its deck with cables or rods from a cable linked to a pillar and a point a certain distance from each pillar
|-
! Filler
|{{Maybe|Real}} method of maintaining {{w|Grade (slope)|grade}}, not really a 'bridge'
|{{w|Embankment (earthworks)|Embankment}}, {{w|Causeway}} or even a {{w|Dam}}
|Serves the purpose of allowing travel across the gap, but by removing (or {{w|Culvert|mostly removing}}) passage through the gap itself. By filling the gap with hard, irregular material (most commonly rocks), support can be provided, while still allowing water to flow through the gaps. Due to the generally small size of the gaps, generally only slow-flowing water can reliably get through.
|-
! Budget Overrun
| {{Yes|Real}} (with an absurd name)
|{{w|Cable-stayed bridge}}
|Specifically, the pictured bridge is a {{w|cantilever spar cable-stayed bridge}}, similar in appearance to the {{w|Samuel Beckett Bridge}} in Dublin or the {{w|Erasmusbrug}} in Rotterdam. Many bridges in this category suffer severe cost overruns. Randall may be drawing upon his local knowledge of the {{w|Leonard P. Zakim Bunker Hill Memorial Bridge|Zakim Bridge}} in downtown Boston's {{w|Big Dig}}, also strongly associated with cost overruns. Also, while not a bridge, the budget overrun and diagonally inclined tower supporting cables may be a reference to {{w|Montreal Tower}} and {{w|Olympic Stadium (Montreal)|Olympic Stadium}}, which has suffered infamous budget overruns, costing over 6.7 times the initially planned amount.
|-
! Jump
| {{No|Not real}}
|Similar to a pair of small {{w|cantilever bridge}}s, constructed at an incline.
|A "bridge" that appears to be being used by a skateboarder, though in a manner far more dangerous than any jump in a typical skatepark. While not {{w|London Buses route 78#History|normally}} a feature of the highway, jump ramps can be used for gap-crossing stunts by almost any vehicle with sufficient speed. Partial bridges, which allow ''some'' vehicles using them to safely cross the gap, iconically featured in {{w|The Dukes of Hazzard}} TV show, as well as common in various {{w|The Man with the Golden Gun (film)#Car stunts|action}} {{w|Speed (1994 film)#Filming|films}}, though typically less easy to use correctly than the setting implies.
|-
! Halfhearted
|{{Maybe|Not}} real under this name, but with real analogs
|[https://www.archdaily.com/184921/moses-bridge-road-architecten Moses bridge]
|The diagram shows that there was barely any attempt to bridge the gap in the landscape at all, just take the 'deck' down into it and back up out again. The concept may have been inspired, in part, by [https://www.fastcompany.com/90186315/the-strange-art-of-the-melting-bridges-of-google-earth an artifact in Google Earth software].
Structures exist, at the {{w|Fort de Roovere}} in Halsteren, Netherlands and elsewhere, that resemble this 'solution', though these would have involved much thought and commitment in their building, possibly more 'hearted', even, than any more conventional bridge design, especially in the provision of stairs to allow easier ingress/egress (at least for foot traffic) than in the comic's version.
|-
! Waterbed
| {{No|Not a bridge}}
|{{w|Waterbed}}/{{w|Fish tank}}/{{w|Swimming pool}}
|Rather than a bridge, it is more like another version of a causeway (see 'Filler') using trapped water to maintain the upper surface.
Named for a 'mattress' type, which is usually a raised surface ''on top of'' a piece of bedframe, with an unusual approach to padding and comfort.
|-
! L'Engle
| {{No|Not real}}
|[https://www.refinery29.com/en-us/2018/03/192728/tesseract-definition-wrinkle-in-time-space-dimension Tesseract AWIT] not {{w|Tesseract|Tesseract (geometry)}} cf. {{w|Einstein–Rosen bridge}}
|References {{w|A Wrinkle In Time}} by Madeleine L'Engle. Characters cross great distances by "tessering", moving via a tesseract through a higher dimension which essentially brings the two ends of the journey together from the perspective of the traveler. The image shows the two ends of the gap being brought together, with the gap apparently crumpled in between them.
|-
! Fun
| {{No|Not real}}
|{{w|Vertical loop}}/{{w|Rollercoaster}}
|It is a loop-de-loop, not normally a practical or necessary way of bridging a gap. Something previously seen, in an arguably even more impractical manner, in [[2935: Ocean Loop]].
|-
! Repurposed Elevator
|{{Maybe|Real}}, but not as displayed
|Horizontal {{w|elevator}}/{{w|People mover}}
|There are various implementations of such designs, but the best-known one is probably the {{w|Schmid Peoplemover|Schmid Peoplemover}}. However, unlike a regular peoplemover, where the door stays upright, the image shows a regular elevator that has been rotated 90 degrees. This not actually its own type of bridge, but just a type of plank bridge where the elevator shaft (or one side of the elevator shaft) is used as a plank - closing the circle to the first image. This could also be a reference to Wellington Station on the Boston Subway, {{w|Wellington_station_(MBTA)#People_mover|where there was a vertical people mover}} over the yard but was later repurposed into a walkway (bridge).
|-
! (Title text)
| {{Yes|Real}}
|{{w|Pontoon bridge}}
|Pontoon bridges are described as a series of fictitious "waterbed bridges", as shown above, but constructed without sides. This would mean that that the 'bed'-supporting water flows in one side and out the other, if there is any passage or tidal flow of water. It may technically mean that you cannot cross {{w|The Same River Twice|the same bridge twice}}.
Pontoons rely upon buoyancy, either of the whole deck or distinct floating elements, whereas an enclosed "waterbed" bridge would rely upon the strength of the membrane to keep the mass of water within it, and thus the deck above that mass.
|}

==Transcript==
:Bridge Types

:[A 4x4 matrix of 16 ways to cross the same rectangular hole in the ground]

:Plank [A plank laid over the hole, with Cueball standing on the left side of the plank, just past the edge of the hole.]

:Rope [A rope bridge with rope guardrail. Cueball is standing in the middle, causing the bridge to sag about one Cueball-length down.]

:Truss [A truss bridge with a triangular truss above the bridge deck. Cueball is visible in the center of the third truss from the left.]

:Trestle [A trestle bridge, slightly higher than the edges of the hole, with small ramps at either end. Cueball is standing about a third of the way from the left.]

:Arch [A straight deck, supported by what looks like three stone or brick arches. Cueball is notably absent.]

:Suspended Arch [A single large arch spanning the entire gap, with the bridge deck suspended from the arch by nine support cables. Cueball is standing approximately in the middle, between the fourth and fifth cables from the left.]

:Draw [A truss bridge split into two parts, the right half supported by a single straight pillar in the hole and the left half being pulled upwards by a large winch. One Cueball is standing on the outermost part of the left half and another is standing on the innermost part of the right half, directly over the pillar.]

:Suspension [A bridge deck supported by cables hung from two pillars and going to the edges of the hole, with smaller cables linking those to the deck. Cueball is standing just left of center on the bridge.]

:Filler [The hole is filled with rocks, which are larger than Cueball at the bottom but diminish in size the further up they are. Cueball is standing a third of the way from the left edge of the hole.]

:Budget Overrun [A bridge deck suspended from a single pillar that starts in the bottom left corner of the hole, then angles to the right such that the top of it is above the middle of the deck. Nine support cables are visible, but another one is likely behind the pillar itself. Cueball is standing between the third and fourth cables from the right.]

:Jump [Ramps are present on both sides of the hole. Cueball, riding a skateboard, is in the air approximately a third of the way from the left, indicating that he has jumped off of the left ramp.]

:Halfhearted [A simple bridge deck, sagging so much that the majority of it is on the floor of the hole. Cueball is standing in the hole, about two-fifths of the way from the left.]

:Waterbed [The hole is now full of water, with two fish and an octopus visible in the water. Two Cueballs are crossing, and seem to be struggling to maintain their balance as the bridge warps and undulates under their feet.]

:L'Engle [There is no bridge; instead, the terrain itself is warped such that the top corners appear to be pulled together to join in the center, with arrows illustrating their movement, although there is still a void in the lower center of the hole. Cueball is hopping from the left protrusion to the right.]

:Fun [The bridge does a rollercoaster-style loop in the center. The entirety of the bridge is supported by vertical struts. Cueball, on a skateboard, is halfway to the top of the loop.]

:Repurposed Elevator [Instead of a bridge, there is an elevator tower rotated on its side, with 7 evenly spaced exits. One Cueball is standing to the left of the elevator tower, one Cueball is on top of it and appears to be hugging it, and one Cueball is in the elevator carriage on the "seventh floor," on the right side of the hole.]

{{comic discussion}}<noinclude>

[[Category:Engineering]]
[[Category:Comics featuring Cueball]]
[[Category:Multiple Cueballs]]
[[Category:Animals]]

3106: Farads

2026-05-16T04:20:28Z

2001:4450:81E7:1E00:E160:C57F:6F73:2376:

{{comic
| number = 2015
| date = November 20, 2015
| title = FDF
| image = star.svg
| titletext = You know what they say--if you don't like the weather here in the Solar System, just wait five billion years.
}}

==Explanation==
{{w|Weather forecasting}} is an extremely difficult task, even if it is only for five days. In numerical models, extremely small errors in initial values double roughly every five days for variables such as temperature and wind velocity. So most {{w|Meteorology#Meteorologists|meteorologists}} only provide us with a five-day forecast.

In this comic [[Randall]] takes this to the extreme by first showing a '''Five-Day Forecast''' and then progressing to five-month, year, million, billion and finally trillion-year forecast, {{tvtropes|WeirdWeather|leading to weather patterns that we don't usually see on a regular basis.}}

Since the first weather symbol is the same in all six rows, we must assume this indicates the weather today (and not tomorrow or in a trillion years). It is first in the second panel that we have made the first jump according to the label. Consequently, the last column gives the predictions for four days, four months, ..., four trillion years from today.

When moving past the five days, the forecast is just a qualified guess based on the time of year. In a month it is Christmas as shown in the second panel of the second row. And then it is winter with January and February so snow is likely, but certainly not something that happens on all days of a winter month.

Looking at the five-year forecast, guesses are made as to what the weather will be like at the same time of year. For these first three predictions the weather symbols are all of the same three types. Sun, clouds and some kind of {{w|precipitation}}, rain or snow. And the temperature range from 21 to 44 °F (-6.1 to 6.6 °C), winter temperature.

Then we go into the far future, jumping a million years from panel to panel. But still the weather symbols stay the same. However, in 3 million years time aliens (or advanced humans) attack with energy beams from something looking like {{w|flying saucers}}. They are gone a million years later. The temperature range is still the same (except that it rises to 52 °F or 11.1 °C, a possible reference to global warming) in one panel. But then while the attack is going on the temperature rises to 275 °F (135 °C).

Once we get to the billion-year mark it actually becomes more meaningful to try to predict the "weather". Because now we reach the times when the {{w|Sun}} begins to change. Although the Sun will continue to burn hydrogen for about 5 billion years yet (while in its {{w|Sun#Main sequence|main sequence|}}), it will still grow in diameter as it begins to exhaust its supply of fuel. The core will contract to increase the temperature, and the outer layer will then compensate by expanding slightly. This is what is indicated in panels two and three where the color of the Sun changes towards red as the surface becomes less hot as it expands away from the center of the Sun. The temperature will rise on Earth as indicated in the panels (105 °F = 40.5 °C and 371 °F = 188 °C). So in two billion years the temperature is hot enough that all the earth's oceans will have boiled away… Actually this will happen already in about [http://phys.org/news/2015-02-sun-wont-die-billion-years.html a billion years].

Then once there is {{w|Sun#After core hydrogen exhaustion|no longer enough hydrogen}} the Sun will truly expand into a {{w|red giant}}. This should not happen until five billion years from now,{{Citation needed}} but in the forecast it is indicated to happen already in three. Maybe this is Randall taking liberties to show what happens during this phase, which would not fit into a five-billion-years forecast. Alternatively it is just indicating how uncertain these kinds of forecasts are, or a statement that we may not know for certain that it will take five not three billion years.
Disregarding this, the fourth panel shows the temperature at Earth's position inside the red giant Sun. The color of the panel indicates that we are inside the Sun. The temperature is 71,488,106 degrees Fahrenheit (39,715,597 degrees Celsius). The current temperature of the center of the Sun is "only" 27 million degrees Fahrenheit (15 million degrees Celsius). And although that may rise by a factor of ten during {{w|Stellar nucleosynthesis|helium fusion}} then that will only be at the very core and not out in the solar atmosphere reaching out to Earth Here the temperature would only be of the order of thousands of Fahrenheit, since the Sun's outer temperature decreases as it increases its diameter. So this panel's temperature also makes little sense. It may involve some ambiguities regarding what the forecast means; the edge of the red giant Sun is predicted to be somewhere near the current orbit of Earth, but the position of the Earth could change. The most likely prediction at the moment is for Earth to move outward, but if the planet is engulfed by the Sun, it would spiral inward, and at some point fall apart. So in some sense "here" for the forecast could become a position deep inside the Sun, where core temperatures could reach 100 million Kelvin.

The red giant phase only lasts half a million years, so a billion years after the Sun has been a red giant its outer atmosphere will for sure have disappeared leaving only a {{w|white dwarf}} to cool down. Given Randall's version of this time schedule, then it will have had about a billion years to cool down, but would still likely be the brightest object in the sky as seen from where the Earth once was. It is not indicated in the last panel, where we just see other stars of the Galaxy. The temperature is down to that of the {{w|Cosmic microwave background|background radiation}}. Today this radiation has a temperature of 2.72548 kelvin = -270.4245 °C = -454.7641 °F. So this is a few degree F colder than what is shown in the comic which states the temperature is -452 °F = 4.26 kelvin. This higher temperature may have been chosen to reflect that even the star light from other stars would increase the actual temperature.

In the last panel with trillion years, we jump right past the Sun's Red Giant phase, to a panel looking much like the one after five billion years with only other stars. Over the next three trillion years the stars become fewer and fewer and dimmer and dimmer as they run out of fuel and fewer new stars form. After four trillion years the background temperature even decreases one degree to -453 °F as the universe keeps expanding and the wavelength of the radiation does the same, thus decreasing its temperature.

The title text is a play on comments referring to fast-changing weather on a more ordinary human timescale, such as Mark Twain's quip "If you don't like the weather in New England now, just wait a few minutes."

A ten days forecast was used in [[1245: 10-Day Forecast]]. In [[1379: 4.5 Degrees]] Randall looked at the weather over long periods of time as well.

===Image using Celsius===

A different user-made version for the picture using Celsius instead of Fahrenheit can be found here: [[:File:five_day_forecast_Celsius.png|Five day forecast in Celsius]].

==Transcript==
:[A grid with six rows of five columns, where each row is labeled to the left. For each of the 30 squares a temperature is given in Fahrenheit at the top left. The rest of the square represents the weather as in a weather forecast (or some other relevant items for the comic), mainly in bright colors. Below are the six labels given above each of their five weather symbols with temperature given below these symbols description.]

:'''Your 5-day forecast'''
:[A bright yellow sun.]
:38°F
:[A grey cloud.]
:41°F
:[A grey cloud with six lines of blue raindrops below.]
:36°F
:[A grey cloud in front of a yellow sun.]
:40°F
:[A bright yellow sun.]
:44°F

:'''Your 5-month forecast'''
:[A bright yellow sun.]
:38°F
:[A green Christmas tree with red presents beneath it.]
:29°F
:[A grey cloud with four snowflakes below.]
:21°F
:[A grey cloud with four snowflakes below.]
:24°F
:[A grey cloud.]
:35°F

:'''Your 5-year forecast'''
:[A bright yellow sun.]
:38°F
:[A grey cloud.]
:25°F
:[A bright yellow sun.]
:36°F
:[A grey cloud with six lines of blue raindrops below.]
:37°F
:[A bright yellow sun.]
:41°F

:'''Your 5-million-year forecast'''
:[A bright yellow sun.]
:38°F
:[A bright yellow sun.]
:52°F
:[A grey cloud.]
:40°F
:[Two red flying saucers (with bright domes) are shooting energy beams downwards. One of the beams seems to impact with something at the bottom of the panel, which then explodes. Two plumes of smoke rises up from below, drifting to the right.]
:275°F
:[A grey cloud in front of a yellow sun.]
:40°F

:'''Your 5-billion-year forecast'''
:[A bright yellow sun.]
:38°F
:[A larger orange sun.]
:105°F
:[A very large red sun.]
:371°F
:[A pale yellow panel with no drawing.]
:71,488,106°F
:[A night sky with many bright stars.]
:-452°F

:'''Your 5-trillion-year forecast'''
:[A bright yellow sun.]
:38°F
:[A night sky with many bright stars.]
:-452°F
:[A night sky with many stars.]
:-452°F
:[A night sky with fewer not so bright stars.]
:-452°F
:[A night sky with few dim stars.]
:-453°F

{{comic discussion}}

[[Category:Comics with color]]
[[Category:Science]]
[[Category:Space]]
[[Category:Astronomy]]
[[Category:Weather]]
[[Category:Aliens]]

3108: Laser Danger

2026-05-16T04:12:04Z

2001:4450:81E7:1E00:E160:C57F:6F73:2376:

{{comic
| number = 3108
| date = June 27, 2025
| title = Laser Danger
| image = laser_danger_2x.png
| imagesize = 684x272px
| noexpand = true
| titletext = To combat the threat, many airlines are installing wing-mounted spray bottles.
}}

==Explanation==
Shining a laser at a plane is a [https://www.faa.gov/about/initiatives/lasers federal crime] in the US, and similarly forbidden in many other countries. A sufficiently powerful laser can disorient, distract and/or blind the pilot operating the aircraft. This can prove particularly dangerous to the safety of the aircraft and its occupants during take-off and landing, when planes are likely to have altitudes and orientations particularly susceptible to laser interference, and are phases that are already hazardous periods of flight. This 'use' of lasers was previously discussed in [[3030: Lasering Incidents]] and [[2481: 1991 and 2021]].

Megan claims that there's another reason why lasering a plane is illegal: to avoid provoking kangaroos into leaping at them. Kangaroos are known to [[729: Laser Pointer|chase and jump onto]] the dots created by laser pointers. Kangaroos also prey on birds, with estimates of 1.3 to 3.7 billion birds killed each year. Of course, a kangaroo would be unable to jump to the height of a flying plane.{{Citation needed}} If the kangaroo were able to reach the plane, it would find itself hilariously outsized, though colliding with the plane mid-air could cause damage akin to a bird strike (e.g. shattered windshield or engine failure). The kangaroo in the image is similar in size to the plane and thus could do significant damage. It is unclear whether the kangaroo is unusually large or the plane is a model aircraft. A similar joke was used in the title text of [[1463: Altitude]].

The laser is shown in green, which have become more popular in recent decades as they offer the highest power for the lowest cost and are most frequently the type used in aviation-related incidents.

The title text alludes to the fact that many kangaroos do not like getting wet, and one of the methods people use to discourage them from a place or activity that is unwanted is to use spray bottles to wet their fur. The spray bottle might also emit a hissing sound, which kangaroos associate with other kangaroos threatening them. The "wing-mounted spray bottles" on aircraft could be a reference to fuel dump tubes, which spray out fuel to lighten the aircraft, commonly used before emergency landings (especially soon after take-off, when a nearly full load of fuel is now more trouble than it should have been). To combat actual physical threats to aircraft in real life, El Al (the Israeli national airline) and government aircraft {{w|Air Force One|used by heads of state}} often have various {{w|Flare (countermeasure)|countermeasures}} installed.

==Transcript==
: Megan: Shining laser pointers at planes is a federal crime. It's incredibly dangerous.
: Cueball: Oh, because it can blind the pilot?
: Megan: That's one reason...

: [A plane is shown, with a green laser pointer aimed at it.]

: [The laser disappears. A kangaroo, approximately the same size as the plane, pounces on the plane and sends it tumbling.]

{{comic discussion}}<noinclude>

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Aviation]]
[[Category:Kangaroos]]
[[Category:Comics with color]]