He also says it was the young Einstein’s genius to explain why. Instead he says regardless of the speed of a light source and regardless of your speed, the “light still travels at a steady 300,000 km/s, completely contrary to classical physics and common sense”. However he doesn’t mention gravitational lensing.

Mastin also says when light moves from one medium to another, its speed “can of course change depending on the new medium’s index of refraction, and this “bending” of light is essentially how lenses work”. He talks about the Michelson-Morley experiment, which “unexpectedly demonstrated that light travels at the same speed regardless of whether it was measured in the direction of the Earth’s motion or at right angles to it”. See for example Luke Mastin’s article on the speed of light and the principle of relativity. Search the internet and you can find lots of articles saying this. But it is said that the speed of light in space does not vary. Note that the speed of sound in air varies, the speed of sound in water varies, and the speed of seismic waves in rock varies. The speed of light in space is said to be constant Other than that, the equation takes the same general form, and the speed of light in space, in “vacuo”, is said to be 299,792,458 m/s or 670,616,629 mph. There’s a reciprocal because permittivity is a “how easy” measure rather than a “how hard” measure. The equation for the speed of light in the vacuum of space is given as c = 1/√(ε 0μ 0) where ε 0 is vacuum permittivity and μ 0 is vacuum permeability. The equation for the speed of a transverse seismic wave is given as c solid,s = √(G/ρ), where G is the shear modulus and ρ (rho) is the density. The latter are “secondary” transverse waves like light waves. The former are “primary” longitudinal waves like sound waves. Of course in seismology we have P-waves and S-waves. Wikipedia says the propagation velocity depends on the density and elasticity of the medium, and is up to 13 km/s in the deep mantle. In diamond it’s circa 12,000 m/s or 26,843 mph. In steel it’s circa 6000 m/s or 13,421 mph. The speed of sound in sea water is circa 1500 m/s or 3,355 mph. Celeritas means swiftness or speed, which varies according to the properties of the medium. See Wikipedia and you can read that the speed of sound “is conventionally represented by c, from the Latin celeritas”. You steer a tank to the left in a similar fashion, by slowing down the track on the left. The mud slows down the wheels on the left, so the car pulls to the left. The sonar waves “veer” rather like a car veers when it encounters mud at the side of the road. So a horizontal sonar wave tends to get refracted downwards: Image from FAS and the US Navy, see course ES310 chapter 20 It’s similar for sound waves in the sea, but there the speed of sound typically decreases with depth. Interestingly enough, the speed of sound typically decreases with increasing altitude, so sound tends to get refracted upwards. At that altitude the speed of sound is circa 295 m/s or 660 mph, which is one reason why passenger jets don’t fly as fast as you might like. That’s about 36,000 feet, which is typical for a passenger jet. It usually decreases with altitude up to about 11 kilometres above sea level.

It would take an infinite amount of energy to make an object reach the speed of light.The speed of sound in air is sometimes said to be 343.2 metres per second or 768 miles per hour. As an accelerating object gains mass and thus becomes heavier, it takes more and more energy to increase its speed. The faster an object travels, the more massive it becomes. Human (walking): 9 years So why can't you travel faster than light? It would take a person more than nine years of continuous walking to travel this distance. How long does it take to get to the Moon? Light travels the 380,000 kilometers (240,000 miles) between the Moon and the Earth in 1.3 seconds. So as it turns out, Einstein could never have caught up with the beam of light that captured his imagination as a teenager! Moon Race Nothing can travel faster than 300,000 kilometers per second (186,000 miles per second). Only massless particles, including photons, which make up light, can travel at that speed. It's impossible to accelerate any material object up to the speed of light because it would take an infinite amount of energy to do so. But Einstein showed that the universe does, in fact, have a speed limit: the speed of light in a vacuum (that is, empty space). Think you can travel as fast as you want? Think again.įor centuries, physicists thought there was no limit to how fast an object could travel.

The thing about being faster than light