The speed of light, typically noted as c in math and physics formulas is 299,792,458 meters per second (186,282 miles per second). Note, this figure is for the speed in a vacuum as light will propagate at different speeds through different mediums.
Here’s the speed of light compared to other fast things (in miles per hour):
Unmanned spacecraft, Helios 1 and 2. 157,082 mph. Light is 4,269 times faster than the fastest vehicle ever built by man.
Manned spacecraft, Apollo 10. 39,665 mph. Light is almost 17,000 times faster.
Jet, SR-71 Blackbird, the world’s fastest jet has traveled at 2,193 mph. Light is 305,799 times faster.
Sound: 768 mph. Very much slower than light. 873,000 times slower.
World’s fastest car, Bugatti Veyron. 267 mph. Pretty fast, but compared to light, it’s 2,511,673 times slower.
World’s fastest bird, Spine-tailed Swift, 171 mph. This is crazy fast for a bird. But almost 4 million times slower than light.
World’s fastest mammal, the cheetah has been clocked at 71 mph. 9.4 million times slower than light.
World’s fastest insect, the dragonfly. One species has been measured at 36 mph.
World’s fastest man, Usain Bolt. While faster than anyone else on the planet at 23 mph, he’s still 29 million times slower than light.
Yuri Gagarin was the first person in space when he orbited the Earth on April 12, 1961. He was only 25 years old at the time. Gagarin was a Russian cosmonaut. A cosmonaut is what the Russians call their astronauts. And for you really young readers, a Russian is what we used to call someone who was from what we used to call Russia, or the former Soviet Union.
Yuri’s orbit was made in the Vostok I and took just one hour and 48 minutes to complete. He became an international hero after his flight. For anyone interested, I encourage you to check out Wikipedia’s page on Yuri Gagarin. He was a very accomplished pilot and sadly, was killed in a jet crash when he was only 34 years old.
By most standards, John Dalton is credited with having been the first to propose (and somewhat prove) that all matter was made of atoms. He did this in the early 1800s in his experiments calculating the atomic weights of gaseous elements. Isaac Newton also proposed such a theory in the 1600s although the technology in his time didn’t allow him to experimentally prove his theory. Even before Newton was the ancient Greek philosopher Democritus who had a similar proposal.
The first scientist to significantly “prove” the existence of atoms was Rutherford who “invented the cloud chamber and used it to show that when thin gold foil is bombarded by helium nuclei (alpha particles), the particles are occasionally deflected by a very large angle, but usually pass straight through. This gave rise to the realization that the gold was composed of atoms, with a tiny nucleus at the middle which could occasionally collide with an alpha particle and send it flying.” [source: newton.dep.anl.gov]
The following physics equations and formula sheets are some of the more useful ones I’ve come across in my recent years as a physicist. Some of these are intended to be used as-is, but you can always pull various equations and formulas from the specific topics you need and create your own.
AP Physics Exam Table of Information and Equations. 8 pages, 285k PDF. This is the sheet provided by The College Board to students when taking the AP Physics Exam. This is one of the more detailed formula sheets available. Current version copyright 2007.
MCAT Physics Equation Sheet. 3 pages, 286k PDF. For use by undergraduate students preparing to take the MCAT. Not as detailed as the AP formula sheet, but each equation has a brief description of its use. Topics include: motion, torque, work and energy, momentum, fluids and solids, waves, E&M, electronics and optics. Source: www.prep101.com. Read more…
One way would be for two people communicating wirelessly to start in a wide-open area and start walking until they could no longer see each other. Of course this is ridiculous. The way it’s usually done, by airports and such, is by looking at predetermined landmarks of known distances. Daytime visibility is defined as the distance in which is is possible to see and identify, with the naked eye, “a prominent dark object against the sky at the horizon.” Read more…
The short answer is because of the nature of the ionosphere of the Earth. The ionosphere consists of several different layers of gases that have become conductive from the bombardment of the atoms by: solar radiation, by electrons and protons emitted by the sun, and by cosmic rays.
These layers, sometimes called the Kennelly-Heaviside layer, reflect AM radio signals, thus enabling AM broadcasts to be received by radios that are a long way from the transmitting station. At night, the ionosphere layers partially dissipate and become an excellent reflector of the short waveband AM radio waves.
Source: The Handy Science Answer Book.
First, the simplest definition of density: it is how heavy something is relative to its size. A pound of rocks weighs the same as a pound of ping pong balls. But the ping pong balls take up a lot more space. Hence, the rocks are much more dense. Another way to look at density is to think of it as a measure of the “compactness” of matter.
More background… at the center of an atom is a very dense core called the nucleus. It’s composed of protons and neutrons (held very tightly together). Surrounding this nucleus in somewhat of a cloud are the electrons. Atomically speaking, the electrons are very far apart and far from the nucleus. Consider this: the entire atom composed of an electron cloud surrounding the nucleus is about 99.9% empty space.
The electrons are negatively charged and repel anything else negatively charged with a very strong electromagnetic force, or EMF. Now imagine a force strong enough to overcome this EMF and compress atoms to a much greater density. This is what happens in old and dying stars– the compressing force of gravity starts to overcome this electromagnetic force. The atoms start squeezing together resulting in what’s called degenerate matter. Stars involved in this process are called white dwarfs and the matter in them can reach a density of one million times that of water.
While this is very dense, it is not the densest state that matter can reach. If the dying star is massive enough, its gravitational force can be powerful enough to overcome the repelling force in the degenerate matter. The center of this body is now called neutronic fluid and these stars are now called neutron stars or pulsars. Now we’re getting pretty dense. A 1cm cube of neutron star material would weigh 100 million tons and if dropped would fall straight through to the center of the earth.
Now for even bigger stars (more than three times the mass of our sun), it can have a gravitational force strong enough to break down even this neutronic matter. After this, there will be no barrier left. The matter can not compress any further and it is basically a single point called a singularity. A star that has collapsed into itself to this point is called a black hole.
Since there is no way to measure anything of this magnitude, estimates are made by estimating the matter outside and near this singularity. If we use matter on Earth as a first order of magnitude, degenerate matter (inside white dwarfs) is about one million times as dense. Neutronium (inside neutron stars) is about one trillion times as dense. And finally, black holes, which are about ten trillion times as dense.
Source: Why Nothing Can Travel Faster than Light. Contemporary Books, 1993.