Tag Archives: speed

What, really, is the speed of sound?

We know that the speed of light seems to be the upper limit for how fast something can travel in the universe. But there’s a much lower speed limit that we’ve only recently (in the grand scheme of things) managed to overcome here on Earth: the speed of sound.

Vapor cone (or ‘shock collar’) around a fighter as it’s getting near to the speed of sound.
image credits Flickr / Charles Caine.

You’ve heard the term before, and you might even know its exact value or, more accurately, values.

But why exactly does sound have a ‘speed’? Is it the same everywhere? And what happens if you go over the limit? Well, one thing is for sure — sound won’t give you a fine for it. It will cause a mighty boom to mark the occasion, though, because going over the speed of sound isn’t an easy thing to pull off.

In Earth’s atmosphere, sound can travel at around 345 meters per second. Let’s take a look at why this limit exists, what says it should be this way, and just why things go boom when you blast through it. But first, let’s start at with the basics:

What is a sound wave

What we perceive as sound is actually motion. Sound is, fundamentally, a movement or vibration of particles, most commonly those in the atmosphere, where we do most of our talking and sound-making.

In very broad lines, any object in motion will come into contact with the particles in their environment. Let’s take talking as an example. When someone speaks, their lungs collide with and push out air that their vocal cords modulate to create certain sounds. This will push the air in their immediate vicinity, which will make its molecules collide with air molecules farther away, and so on, until the motion reaches the air particles next to you. They will then collide with your eardrums, which ‘translates’ it into the sensation of sound.

File:CPT-sound-physical-manifestation.svg - Wikimedia Commons
Two ways to represent the physics of sound. Areas with more dots (corresponding to peaks) show high air pressure, while whiter areas (corresponding to throughs) show areas of low pressure that interact to create sound. This pressure is generated by moving air.
Image via Wikimedia.

So from a physical point of view, sound behaves quite like waves do on a beach. Its volume is directed by how high the wave goes (amplitude) and its pitch is formed by how often these waves hit the shore (frequency). The farther a wave travels, the less energy it has (so the less pressure it can exert on new particles), which is why eventually sound dies out and we can’t hear something halfway around the world. More on sounds here.

The speed of sound is essentially the speed that these ‘acoustic waves’ can travel at through a substance. Leading us neatly to the role these substances (called “the medium”) play here.

Not all things are equal

The source of sound only plays a limited part in its propagation. Sound propagation is almost entirely dependent on the medium.

Video credits Reddit user renec112.

First off, this means that sound can’t propagate through void, as there is nothing to carry it. One handy example is that in space, nobody can hear you scream; but if you place your visor on another’s astronaut’s visor, they will. Secondly, a medium can’t carry sound unless it has some elasticity, although this is more of an academic point as every material is elastic to some degree. The corollary of this is that the more elastic our medium, the faster sound will travel through it.

Elasticity is the product of two traits: the ability to resist deformation (its ‘elastic modulus’ or rigidity) and how much you can alter it before it stops coming back to its original shape (its ‘elastic limit’ or flexibility). Steel and rubber are both very elastic, but the former is rigid while the later is flexible.

Density has a bit of a more complicated relationship to the speed of sound. Density is basically a measure of how much matter there is in a given space. On the one hand closely-packed, lightweight particles allow for higher speeds of sound as there’s less empty space they need to travel over to hit their neighbors. But if these particles are heavy and more spread apart, they will slow the sound down (as big, heavy particles are harder to move). Sound will also attenuate faster through this last type of material. In general, elastic properties tend to have more of an impact on the speed of sound than density.

A basic example involves hydrogen, oxygen, and iron. Hydrogen and oxygen have nearly the same elastic properties, but hydrogen is much less dense than oxygen. The speed of sound through hydrogen is 1,270 meters per second, but only 326 m/s through oxygen. Iron, although much denser than either of them, is also much more elastic. Sound traveling through an iron bar can reach up to 5,120 m/s.

One other thing to note here is that fluids only carry sound as compression waves (particles bumping into each other in the direction the wave is propagating. Solids carry it both as compression and shear waves (perpendicular to the direction of propagation). This is due to the fact that you can’t cut fluids with a knife (they have a shear modulus of 0). A fluid’s molecules can move too freely from one another for such motions to create such waves.

Sonic boom

So far we’ve seen that sound has a maximum speed it can travel at, based on which material it is propagating through. By ‘travelling’, we mean particles bumping into their neighbors creating wave-like areas of pressure.

So what happens when something moves faster than the speed these particles can reach? Well, you get a sonic boom, of course.

Slow-motion footage of a bullet traveling through ballistic gel. Notice how the gel in the middle is pushed away by the bullet before its edges and corners have time to move. The process is very similar to how airplanes form sonic booms. You can see the metal table buckling under the pressure. That shock corresponds to a by-stander perceiving the sonic boom after the bullet has passed them.
Image via YouTube.

Despite the name, sonic booms are more like sonic yelling. When an object is moving faster than sound can travel in its environment, it generates a thunder-like sound. Depending on how far away the source is, this boom is strong enough to damage structures and break windows.

An airplane moving faster than the speed of sound will compress the air in front of it, as this air can only move at the speed of sound. It can’t physically get out of the way fast enough. Eventually, all this compressed, moving air (which is, in essence, sound) is blasted away from the aircraft’s nose at Mach 1 (the speed of sound through air). If anyone is close enough to be reached by this blast of ultra-pressurized air, they hear the sonic boom.

Although it is perceived as an extremely loud burst of sound by a static observer, the sonic boom is a continuous phenomenon. As long as an object moves faster than sound, it will keep creating this area of ultra-compressed air, and leave a continuous boom in its wake. One nifty fact about sonic booms is that you can’t hear them coming — they move faster than sound, so you can only hear them after they’ve passed you.

Humans have only recently gone above the speed of sound, with the first supersonic flight recorded in 1947. Since then, such flights have been banned above dry land in the US and EU, in order to protect people and property (although they can still be carried out with proper authorization). Faster-than-sound travel, however, is still an alluring goal. One way to allow for supersonic speeds without blasting all the windows in the neighborhood is to travel through a vacuum or low-pressure air — a cornerstone idea of the Hyperloop.

Fastest ant in the world lives in the Sahara and it runs for dear life — at around 85 cm per second

The Saharan silver ant (Cataglyphis bombycina) is the fastest ant found so far, a new study reports — and, relative to its body size, one of the fastest animals out there.

Head view of the Saharan silver ant.
Image credits  www.AntWeb.org.

When measured in body lengths per second, this petite ant is, hands-down, one of the fastest animals we’ve found so far. At a speed of 855 millimetres (33.66 inches) per second, the Saharan silver ant moves roughly 108 times its body length per second. Cheetahs, for comparison, can only manage 16 body lengths per second, while Usain Bolt can only pull off 6.2. A human going at 108 body lengths per second would move at around 800 km (around 500 mi) per hour.

Small but fast

While birds do have a special place on the ‘fastest animals’ list, they also have the unfair advantage of being able to fly. If you only consider running speeds relative to body size, however, the ant is the third-fastest animal alive. First comes the Californian coastal mite (Paratarsotomus macropalpis) at 322 body lengths per second, and the a species of tiger beetle (Cicindela hudsoni) at 170 body lengths per second.

The ant’s incredible speed is an adaptation to its scorching home in the Sahara. While most animals there avoid going out during the day like the plague, the Saharan silver ant adapted to survive the burning sands. The ants have longer legs than their relatives to keep their bodies farther up from the sand and the heat it gives off. Their bodies also produce heat shock proteins before even leaving the nest, for maximum heat resistance. The ants are also able to track the Sun to help them navigate (so they spend as little time outside as possible), and are covered in hairs with a triangular cross-section that reflects and dissipates heat. Finally, they move really fast — also important when trying to get out of the sun.

Dorsal view of the Saharan silver ant.
Image credits  www.AntWeb.org.

Put all of these features together and the ants are able to go out in the baking desert sun for a few minutes at a time, scavenging carcasses for food.

To find out exactly how fast the ants move, biologists from the University of Ulm in Germany decided to film them using a high-speed camera. They first located a nest in the desert and attached an aluminum channel to the entrance, with a feeder at the end, to lure out the ants. In addition, the team carefully excavated a nest and brought it back to Germany, to see how the ants moved in cooler temperatures.

“After the ants have found the food – they love mealworms – they shuttle back and forth in the channel and we mounted our camera to film them from the top,” said biologist Sarah Pfeffer, first author of the study.

The team reports that the ants operate at maximum efficiency in the desert, reaching speeds of up to 855 millimeters per second. In the cooler environment of the lab, they would leisurely stroll around at 57 millimeters (2.24 inches) per second. The secret to their speed is in the gait, the team reports. The Saharan silver ant can swing its legs at speeds up to 1,300 millimetres per second and extends its stride from 4.7mm to 20.8mm as it reaches higher speeds.

At full gallop, all six of the ant’s feet hit the ground at once, and only stay there for around 7 milliseconds. The team believes this helps the ant keep its tiny ant feet cool and prevents them from sinking in the sand.

The paper “High-speed locomotion in the Saharan silver ant, Cataglyphis bombycina” has been published in the Journal of Experimental Biology.

Sagittarius A*

Researchers find black hole that spins almost as fast as (we think) they can spin

New research led by members from the University of Southampton has identified a black hole spinning around its axis near its maximum possible speed.

Sagittarius A*

A simulated image of supermassive black hole Sagittarius A*, showing against a background of radiation and bright matter swept into the event horizon. The image was generated with data recorded by the Event Horizon Telescope.
Image credits National Radio Astronomy Observatory,

The study involved an international team of astronomers. Starting from observations taken with state-of-the-art sensors, the researchers found evidence that 4U 1630-472, a stellar-mass black hole in our galaxy, is rotating really, really fast — around 92% to 95% of a black hole’s theoretical maximum rotational speed.

Material keeps falling into this black hole as its spinning, being subjected do immense gravitational stress and temperatures. The environment is so violent that this matter shines brightly in X-rays, the team reports, which they used to establish that 4U 1630-472 is rotating and calculate its speed.

So fast it’s glowing

If a black hole is rotating rapidly enough, it should — according to the general theory of relativity — distort space-time around it differently than a non-rotating black hole, the team explains. Such distortions would leave a measurable trace on the radiation emitted by the matter it’s absorbing.

Therefore, researchers can look at a black hole’s emission spectra to determine the rate it’s spinning at.

“Detecting signatures that allow us to measure spin is extremely difficult,” says lead author Dr. Mayukh Pahari from the University of Southampton. “The signature is embedded in the spectral information which is very specific to the rate at which matter falls into the black hole.”

“The spectra, however, are often very complex mostly due to the radiation from the environment around the black hole.”

Dr. Pahari says the team was “lucky” to obtain a spectral reading directly from the matter falling into the black hole, sans the background noise. Armed with that data, it was “simple enough to measure the distortion caused by the rotating black hole,” he says.

The findings from this study are significant, as this is one of only a handful of times we’ve managed to accurately measure a black hole’s spin rate. Only five other black holes have shown high spin rates, the team adds. Astronomical black holes can be fully characterized by mass and spin rate. Therefore, measuring these two properties is key to understanding some extreme aspects of the universe and the fundamental physics related to them.

The paper “AstroSat and Chandra View of the High Soft State of 4U 1630–47 (4U 1630–472): Evidence of the Disk Wind and a Rapidly Spinning Black Hole” has been published in The Astrophysical Journal.


Why bigger isn’t necessarily faster: a look at animal speed limit

Why aren’t the fastest animals on Earth also the biggest? That might sound like a silly question but you’ll be surprised to learn scientists have been trying to answer it for decades. This non-trivial problem is very important because understanding the limits of locomotion also tells us how animals interact with their environments, how they migrate, and, ultimately, how well they can adapt to climate change. Now, German researchers have finally found an acceptable theoretical framework that can predict the speed limits of any given animal, from fruit flies to blue whales, by measuring body size alone.

At a top speed of 120 km/h, the cheetah (Acinonyx jubatus) is the fastest land based animal in the world. Credit: Pixabay, UGVERTRIEB.

At a top speed of 120 km/h, the cheetah (Acinonyx jubatus) is the fastest land based animal in the world. Credit: Pixabay, UGVERTRIEB.

A human step travels a far greater distance than that of a mouse, as does an elephant’s step compared to a human. At the same time, it’s obvious that the biggest animals aren’t the fastest. For instance, the cheetah, which is the fastest land animal, and the peregrine falcon, the fastest bird, are far from being the biggest animals in their class. Speed is a measure of how far a body moves in a given time frame. It follows that, ultimately, what determines an animal’s speed is not only how far a single cycle of movement gets you but also how frequently these cycles occur.

Over the years, scientists have proposed various explanations to account for why larger animals are slower than smaller species, ranging from morphological constraints to how adapted bones and muscles are to the strain of high-speed locomotion. The trick is that these explanations have to apply uniformly across all species of animals, which has so far always proven frustrating. Hirt and colleagues, however, seem to have done it. What’s more, their framework can accurately predict the speed limit of terrestrial animals as well as aquatic or flying ones based solely on body size.

Essentially, the new hypothesis is based on the notion that animals can sustain acceleration for only so long from a starting point. When this critical maximum value is reached, we’ve reached top speed. To accelerate, an animal must release the chemical energy stored in cells into mechanical energy by metabolization in fast-twitch muscle fibers. The fast-twitch fibers can contract and bend for as long as they have fuel so the time available for acceleration corresponds to the number of these muscle fibers.


Credit: Nature Ecology & Evolution.

Large animals have more fast-twitch muscle fibers compared to smaller species but, at the same time, they also take longer to reach any given absolute speed compared to smaller species. This interplay of factors means there’s a threshold beyond which the time required to accelerate to faster speeds will exceed the finite amount of time available for acceleration. In other words, large animals run out of fuel before they get the chance to reach the desired speed. This explains the inverted U-shaped pattern across species that scientists have long ago established.

When 474 animal species ranging from mollusks to whales were modeled, the outputs were a good fit to the predictions that maximum speed drops off steeply as animals grow beyond intermediate sizes. Bearing this model in mind, it’s animals of an intermediate size such as the cheetah or falcon that are the fastest despite having smaller muscles or fewer muscle fibers than their larger counterparts. Yet the model is still not perfect since there are some variations in locomotion performance among similarly sized animals. For instance, humans are near the peak of the model’s predictions for terrestrial locomotion yet we fall dismally short of this prediction in the real world.

The findings will prove useful for scientists who are busy studying various ecosystems and how these interact with one another. Building on Hirt’s model, scientists might also be able to tease answers to other pressing questions bugging biologists. For instance, land and air-based endotherms are typically faster than ectotherms of similar size but in aquatic environments, this pattern is reversed.

Stunning pictures of drugs as you’ve never seen them before

Most people have a heart time putting into words what they experience when under the influence of some psychoactive drug – but Sarah Schönfeld decided to make this experience visual. The experiment was meant to transpose the change into another kind of sensory experience, so she put drugs on a photonegative and then enlarged the image. The goal was observing the reaction of negative film to both legal and illegal combinations of substances to which it was exposed. Here are the results:



SPEED – methamphetamine, C10H15N, it is a very powerful stimulant, chemically related to amphetamine, but with more severe side effects. It is a white, odorless, bitter-tasting powder that easily dissolves in water or alcohol.

Speed + Magic

Speed + Magic

SPEED + MAGIC – the combination between methamphetamine and mephedrone also lies in the category of amphetamines. Although there are the long-term effects that are more serious, there have been reported cases with people hospitalized because of the short-term ones.



MAGIC – mephedrone’s main effects include euphoria, alertness and a strong feeling of affection towards anyone around the consumer. On the bad side, there are paranoia and anxiety.



MDMA – ecstasy or X, short for 3,4-methylenedioxymethamphetamine, is another amphetamine. The typical effects would have to be somewhere between 3 to 6 hours, and the consumer will feel alert and hyper at first, maybe lose track of time.



LSD – lysergic acid diethylamide is a psychadelic drug from the ergoline family. Some of the most common psychological effects are synesthesia, an altered sense of time and spiritual experiences.



KETAMINE (Special K)- anesthetic, also a pain killer. When taken excessively leads to a special kind of hallucinations.



HEROIN – diacetylmorphine or morphine diacetate is an opioid analgesic and it’s associated with tolerance and strong physical dependence.



GHB – 4-hydroxybutanoic acid is a substance naturally found in the human central nervous system. It is an aesthetic, but a recreational drug as well.



ECSTASY – Recreational drug, its most common psychological feelings are lack of anxiety and a sense of intimacy, euphoria and mild psychedelia.

Crystal Meth

Crystal Meth

CRYSTAL METH – metamphetamine, psychostimulant used as a recreational drug. Used in small amounts, it gives a boost of energy.



COCAINE – benzoylmethylecgonine is a stimulant, appetite suppressant, it is considered more dangerous than the entire amphetamine drug class.



CAFFEINE – bitter, white, crystalline xanthine alkaloid, it paralyzes and kills some insects when found in natural environments.




ADRENALINE – epinephrine is a hormone and a neurotransmitter, it’s mostly used in medical purposes. Occasionally, there are situations in which it’s used as a recreational drug.



VALIUM – Diazepam, it’s used in treating anxiety, panic attacks, insomnia. Anterograde amnesia is one of the side effects, as well as sedation.

EDIT: We originally had a wrong title for this, claiming that these are images taken under a microscope. Sarah Schoenfeld was kind enough to contact us and fix that error.

We now know the birth place of the biggest guitar in the galaxy

guitarIn case you’re wondering, the biggest ‘guitar’ in our galaxy is in fact a pulsar that was nicknamed The Guitar Pulsar. It’s basically a stellar corpse that emits a beam of electromagnetic radiation that just shreds interstellar gas, creating a wake of hot hydrogen shaped just like a guitar.

Little is known about these remnants, from any point of view. In order to track down it’s birthplace, Nina Tetzlaff at the University of Jena in Germany and her colleagues calculated the location of 140 groups of stars, as they were 5 millions ago.

The pulsar was practically launched from a cluster of massive stars, moving at about 1500 kilometres per second, which is just huge. They were able to pinpoint the exact location it was formed, but why it moved so fast still remains a mystery. Speeds over 1000 km/s are practically not used in current astronomy models, and are considered by many to be borderline impossible.

Hubble shows 2 galaxies that are just losing it

hubble-ram-pressureRam pressure is the pressure exerted on a body when it passes through a fluid medium; this causes a drag force that is exerted on the body. The same pressure occurs when a galaxy (body) is moving through an intergalactic gas (fluid), and in this case, the ram pressure can sweep a significant part of the intergalactic gas from the galaxy. The spiral galaxy NGC 4522 is located a bit more than 60 light years away from our planet and it’s a great example of a spiral galaxy being stripped of its gas.

The galaxy is part of the Virgo galaxy cluster and it moves at over 10.000.000 km/h. This is just an image, but you can almost see the galaxy swirling, highlighting its dramatic state, as the halo-like gas is being forced out of it. This was caused by a number of newly formed star clusters.

The image also shows some more subtle effects of the ram pressure, such as the curved (convex) appearance of the disk and understanding it is really important because it helps researchers understand the mechanism that leads to the birth of galaxies better, and also provide important clues on how the rate of star formation is being ‘controlled’ by galaxies.