terminal velocity

[druiaghtagh]

i always understod that falling objects reach a terminal velocity, is this correct ?

[sddsddean]

It is true in an atmosphere. Eventually you will reach a velocity where you cannot overcome air resistence. So a piece of paper will have a terminal velocity of naff all, whereas a bowling ball will be a lot faster. Also, at height, where the air is thinner, the velocity will be greater. It then follows that if you are in a vacuum(space), you will continue to accelerate as long as you are acted on by an outside force (eg gravity). However, you then start entering the realms of relativity, which says you cannot go faster than the speed of light, so you must reach a sort of terminal velocity, but I was never that good at A level physics, so I'll quit while I'm ahead!

[lisaj]

sddsddean: Indeed, as an object's speed increases so does it's mass. Now since f=ma (Newton), to maintain a constant acceleration on that object, you'd need an ever increasing force in correlation with its ever increasing mass. Note that the objects velocity doesn't decrease, but rather the rate at which its speed increases does.

With respect to the original question sddsddean is bang on. Terminal Velocity is achieved when drag forces equal accelerative forces (Eg. gravity).

[xyzzyplugh]

Also of interest, the Galileo experiment. Which I have repeated; but not from the Tower of Pisa; a small rock and a boulder launched together, do indeed fall and land simultaneously. It's weird to see in action I always expect the boulder to hit first. Not so.

[gazzawazza]

Well, this may be another of those questions where I'm wrong, but I'm sure I was taught at school that falling objects increase in speed initially but eventually (if they fall for long enough) they get to a point where they fall at a constant speed.

I'm sorry I can't give a reason why exactly but it was something to do with the formula and gravity becoming equal to each other or something.

[sddsddean]

Galileo's experiment was also carried out on the Moon by an Apollo astronaut using a feather and a hammer. His quote was "How about that? Looks like Mr Galileo was right!"

[rja211077]

gazzawazza: you're almost there. just substitute "the resistive force" (i.e. air resistance) for "the formula"(?!) and you're spot on. When the two forces (air resistance and gravity) acting (in opposite directions) on the object balance, the resultant force F = zero and therefore according to F = ma acceleration is also zero (i.e. constant, or 'terminal', velocity). Whichever correspondent said that mass increases with speed is wrong.

[gazzawazza]

Thanks rja211077, being 40 now my memory seems to get worse by the day, but there are certain things I'm sure I'm sure of, I think...! Now I just need to understand the formula (which I did understand at school) to help me get my head round this...

[KARL]

The matter of mass increasing is part of Einstein's theorem, which holds that by the time you reach the speed of light ....