what is the difference between an asteroid and a metior and a comet ?

You only get ONE question! 

Asteroids are minor planets. 

A meteor is a meteorite which is a small rocky or metallic body in outer space. Meteorites are significantly smaller than asteroids. 

A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. 

An asteroid is a small rocky object that orbits the Sun. A meteor is what happens when a small piece of an asteroid or comet, called a meteoroid, burns up upon entering Earth's atmosphere. Read on to find out more and learn the difference between asteroids and comets, meteoroids and meteorites, and more!

A comet is a big rock that has ice in it and is in outer space. An asteroid is a rock in space. n asteroid becomes a meteor when it enters an atmosphere.

Meteors are the visible effect of debris (normally rocks and pebbles, but ices are possible) hitting the atmosphere at from 10 to 25 miles/second.  This heats the compressed air molecules, providing the streaks of light seen, usually at altitudes of 60 to 75 miles.  A surviving piece found on the ground is called a meteorite.

There is one record of a woman in Georgia (USA) suffering a dislocated shoulder when hit by a meteorite in 1953.  It had gone through her roof and second floor before hitting her.

There is an unconfirmed rumor that the Tunguska impact of 1908 created a shock wave that knocked a man off his porch, causing injuries he died from the next day.

Latvia has an impact crater dating back ~4000 years with all sorts of nasty legends associated with it, including many deaths at the impact.

Odds of any kind of impact from space (meteor or stray spacecraft) harming a human extremely remote.

If only there was some way to look up their definitions.

An asteroid is a small rocky object that orbits the Sun. A meteor is what happens when a small piece of an asteroid or comet, called a meteoroid, burns up upon entering Earth's atmosphere.

In the mid-1800s, there was a debate whether the newly discovered "planets" between Mars and Jupiter (namely, Ceres, Pallas, Juno and Vesta) were real planets or pieces of something else.

Up to then, it was easy to distinguish (through telescopes) whether something was a star or a planet: planets showed a disk while stars were point-like.  The four new planets (and all the ones that were later discovered in the same band of orbits) appeared to be tiny points: they were "asteroid" in shape (originally, the word was an adjective meaning "looks like a star").

Objects that showed some distinct size were called "planetoid" (appears like a planet).

A few years after that (when more and more "asteroid" objects were found in orbit around the Sun), these smaller objects were classed as "minor planets" (and, more recently, some of the bigger ones of these were stuck in a middle category called "dwarf planets").

The word star comes from a Greek word "aster" that represented any object seen in the heavens.  Most of these were fixed stars (they are the ones we see forming the constellations, for example).  Some of them moved in a predictable way among the fixed stars. They were called "aster planetes" (wandering star) from which we got the word planet.  Back then, the Sun and the Moon, being objects in the sky (aster) and known to move predictably among the fixed stars (planetes) were considered planets.

Some stars moved unpredictable AND seem to have a head with hair flowing from it (the tail flowing out of the coma). They were called "aster cometes" (stars with hair). A comet is a piece made mostly of different types of ices (including water ice) with dust and pebbles throughout the ice. As it moves colower to the Sun in its orbit, it releases gas and dust which, under the pressure of sunlight, form a tail (or two) that seem to trail the head.

The word "meteor" comes from a Greek word that means "high".  It was already known that meteors (sometimes called shooting stars) are objects very high in the atmosphere.  It is a streak of light caused by the arrival of an object coming in at very high speed and pushing its way through the air. The shock wave caused by the object hitting the air is what causes the glow of light.

Most of the time, the energy from the shock wave will grind the "thing" to dust. It does not survive the fall through the air.  IF it does, then the piece of rock that is found on the ground is called a "meteorite" (= mineral from a meteor).  In the days before people understood that they came from space, they were called "aeroliths" (= stones from the air).

The modern tendency is to call (in retrospect) an object that fell in from space to cause a meteor (the streak of light high in the atmosphere), a "meteoroid". If this object happens to be big enough to cause a meteorite (implying that was was around 15 feet before entering the atmosphere), then some of us call it an asteroid. However, this distinction is not official (at least, not yet).

By the time a meteoroid goes through the roughly 400 km (250 miles) of atmosphere, it will either have disappeared (as dust mixing itself with the air) or the remaining pieces will have slowed down quite a bit. Some people have been hit by such pieces and they did not even have their skin pierced (but some did suffer broken bones).

Only much larger pieces can reach the ground with high speed. We are talking about pieces measuring over a hundred meters (call it 350 feet across). At that size, it will not go through your head and leave a hole. It would simply splat all of you into a pancake, along with anyone standing close enough to you.

>>what is the difference between an asteroid 

>>and a metior and a comet ?

An asteroid is a small, rocky or metallic body orbiting the Sun in some fashion. They may contain some ice, and may be a mix of rocky material along with metal. 

Take that same rocky, metallic body - and throw it into Earth's atmosphere... now, it's a meteor.  We see meteors zipping across the sky every so often at night, and some are pretty spectacular.  (If it survives the trip through our atmosphere, and hits the ground, then it's a meteorite.)

A comet is also a body that orbits the Sun, but in general, they are composed much more of different ices - frozen water, methane, CO2, etc.  They usually orbit quite far out from the Sun, and occasionally, something will 'knock' them in toward the inner solar system... when that happens, the surface of the body may begin to melt, and the frozen ices are blown out by the solar wind, creating the familiar tail we know comets have.  As it whips around the sun, the tail always points away from the sun, due to the out-flowing solar wind.  Comets are called 'dirty snowballs', as there can be rocky material mixed in with the ices in it's mass. 

>>and on average, how many times does debris from either of these hit our planet ?

Thousands.  Every couple of seconds, a small bit of matter may be entering our atmosphere, somewhere...  The larger it is, the rarer it is - so, we'll see 'Shooting Stars' every so often  - which is the size of sand grains;  but a larger rock will appear brighter, and last longer in the sky.  If it's large enough, it may survive all the way to the Earth's surface. 

>>final question, what are the odds of a tiny 

>>pebble sized piece of debris from either 

>>of those striking a human being on earth, 

>>and would it not be travelling at astonishing 

>>speed, fast enough to 'slice through flesh 

>>as if it wasn't even there ?

Well, the only verifiable event that a person was actually struck by a meteor - was a woman struck by one that crashed through the roof of her house, and bounced off furniture, striking her.  

There is a story of a man struck in Italy in the late 17th century, (and he was killed), and there was a young boy in Uganda that had been injured by a meteor as well. 

(here:  https://en.wikipedia.org/wiki/Sylacauga_(meteorite... ) 

So... When a meteor enters Earth's atmosphere, it's usually moving very fast - 20,000 to 50,000 mph; and it heats up & begins to vaporize. Sometimes, the sudden heat causes the rock to explode into fragments, or simply break apart into a few shards. The entry into the atmosphere slows the rock a lot (depending on it's size and shape) - but, it's going to have some velocity to it - several hundred miles per hour would be possible, depending on it's entry angle.... and, like dropping an anvil on the Coyote's head in those Road Runner cartoons - it can have a deadly impact.  Even if the rock has been slowed by the atmosphere, and reached it's terminal velocity - imagine being hit by a stone that someone had thrown off the Empire State Building - it's going to do some damage, or even kill you - if it hits you. 

> what are the odds of a tiny pebble sized piece of debris from either of those striking a human being on earth?

Zero. A pebble would hit the athmosphere with such an amount of speed/energy that it would burn up and/or evaporate way before it could land. It would need to be a *lot* bigger for part of it to actually hit the ground

Whether you would be alive enough to realise that a bullet went through your brain depends on what brainparts were affected

Meteors are from the debris and remnants of past comets Only meteorites hit the Earth!

Asteroids are much larger bodies normally in orbit.

Chances of being hit are much smaller that dying from a coconut hitting you in the head killing you.