xkcd.WTF!?

Explanation ➲

The slingshot (in this comic, styled "Regular Slingshot") is primarily refering to the hand-held device used for accelerating small projectiles, such as stones or steel balls. The "forked stick and elastic" contraption (known as a catapult, in the UK) acts by a pull-back-and-release action, and has become associated with youthful recklessness (or an outright tendency towards vandalism), but is also the basis of manufactured sport/hunting devices as well as all of the more organic child-made contraptions.

The gravitational slingshot, or gravity assist, is not a device but a term used to describe how gravity can significantly alter the path of an object in space, such as a spacecraft or an asteroid. A gravitational slingshot generally involves a small object passing by a much more massive object, which turns the smaller object's trajectory, trading momentum and kinetic energy between the two bodies. The smaller object can undergo a large change in velocity, "paid for" (in the sense of conserving the momentum and energy of the system) with a negligible change in the velocity of the more massive body.

This comic humorously compares the two, in tabular format.

	Regular slingshot	Gravitational slingshot
Used for hunting	✓	X
Used for sport shooting	✓	X
Used for spacecraft propulsion	X	✓
Large online enthusiast community	✓	✓
May have caused dinosaur extinction	Probably not	Maybe
Used by Dennis the Menace to terrorize Mr. Wilson	✓	Not yet, but I'm pitching a reboot

The first four categories accurately reflect reality. As a hunting tool (and as an offensive weapon), recent designs have been claimed to propel a projectile with more force than .22 and .38 caliber pistols. Consequently, several communities have prohibited the possession of such slingshots, which may be called "wrist rockets". The state of Massachusetts, where cartoonist Randall resides, is one of those communities. Gravitational slingshots would be inefficient and cause overkill for such purposes, as well as being difficult to achieve sufficient accuracy and specificity.

Conversely, gravitational slingshots are a useful way to change the velocity of a spacecraft without having to use large amounts of fuel, whereas building a regular slingshot capable of propelling a spacecraft is likely to be impractical - not to mention the destructive/fatal consequences, to vehicle and cargo, of near-instantaneous acceleration to useful speeds, such as the Mach 33 required for an object at sea level to escape Earth's gravity, especially when there's an atmosphere present.

Both types of slingshot excite interest among many people who may form online communities to discuss them, but for quite different reasons, and the size of overlap between these communities is uncertain.

The fifth category ventures into the absurd, at least with respect to "regular" slingshots, which did not exist (as far as we know) at the time of the Cretaceous-Tertiary extinction event. (Humans, which invented them, did not exist at that time. Use of slingshots would therefore require some other contemporaneous intelligent species to have invented them, or some kind of time travel.) However, it is likely that the event resulted from the impact of a space-rock that was perturbed into an Earth-crossing orbit by a planet such as Jupiter, given at least a minor gravitational slingshot on its way to eventually crashing into the Earth.

The sixth category references the long-running comic and cartoon character Dennis the Menace (USA), in which the titular character unintentionally harasses neighbor Mr. Wilson with (regular) slingshots and other devices and behaviors. In Randall's projected reboot of the franchise, which is elaborated on in the title text, Dennis trades his regular slingshot for a gravitational slingshot. By miscalibrating his ammunition, or the force of his slingshot, he turns a demonstration ("a nice comet") into a destructive event (the loss of Wilson's dinosaur garden). The reference is to the relative size and velocity of the space objects responsible for, respectively, comets and "meteors" versus asteroid impacts.

This comic may have been inspired by the recently released movie Slingshot.

This is very similar to 2844: Black Holes vs Regular Holes.