OK Mr. Wizard, explain escape velocity to me.

[kcollins4]

Consider a black hole. Small, dense, huge mass. Light does not escape from it because at 186,000 mps, it still has not achieved the escape velocity of the gravity of the black hole. Without a propulsion system, or mass, it's constantly moving at the same speed, but it never escapes the pull.
I guess what's hard for me to grasp is that the escape velocity is an "instantaneous from start" speed, versus a prolonged slower speed.
Anyway...interesting discussion. More responses than I expected.
Ya Mark, I wanted to be an astronaut in '69.

 

[crexrun]

My primitive brain is thinking the same thing as echowars, with a constant push, there should be absolutely no reason you need that kind of speed, if there was a constant propulsion. How about this to simplify it, if we could somehow pull from space, you could hook a rope up to a bike and pull it right off the planet. The same goes for the space sidewalk, just like walking up a hill, except you'd need to bring more water.

I think it's probably been explained pretty well already, there's nothing technical I can add to this, but I know that you need a pretty good velocity to kick a football over a house, and even though it accelerates pretty fast, it's not an instant start, it goes from 0 to whatever as your foot pushes it. The only reason the space shuttle has to go that fast is to maintain the kick. It starts out very slowly, it's kinda heavy. I'm sure it hits a top speed of 25k, but it can't maintain that the whole distance, so it relies on a large burst of speed, and coasting the rest of the way. As soon as the booster rocket breaks away, it's decelerating, but it's already reached such a velocity that it can break away from gravity.

If a helium balloon could take it, could it travel to space? Of course it wouldn't like the vacuum in space very much, but imagine how big a ballon would get in a complete vacuum! My head hurts, I'm gonna go work on a power tool. Crexrun

 

[crexrun]

can anything be "instantaneous from start?" Doesn't everything have an accelerative curve, a bullet, light, my dad's beat up pick-up? I seem to remeber that everything does, but maybe light doesn't. You just need to run really fast to snap the rubber band. remember the road runner? Hope you get it figured out, Crexrun

 

[piece-it pete]

...of which there's half a dozen
on the face of my resorts. :saywhat:

Remember the "Room-a-Zooms" you had when you were drunk as a teenager!....well ...thats not quite the same ...but it felt the same way!!!....the 'drunker' you were...the more you felt like you were gonna fall off the face of the Earth!!....I know !!!!I been there! lol!...

So escape velocity is... 4 quarts?



Pete

 

[markthefixer]

How the hell does that apply?

Doc

Trying to illustrate potential energy. Shoulda said "orbital height" rather than orbit, or "from 30,000 feet the hammer would go through a roof, rather than bruising a toe".

Guess it kinda fell flat......


(I did like the book....)

 

[usedto]

You Can't Get There From Here!

 

[Dr. Strangelove]

Trying to illustrate potential energy. Shoulda said "orbital height" rather than orbit, or "from 30,000 feet the hammer would go through a roof, rather than bruising a toe".

Guess it kinda fell flat......


(I did like the book....)

Sorry, still not buying it. From 30,000 feet, you would be sharing space with 767s. The velocity of the hammer would max out at around 250 mph. And this is a discussion about escape velocity, not terminal velocity.

Doc

 

[RichPA]

Ya Mark, I wanted to be an astronaut in '69.

Me too!

 

[crexrun]

not trying to hijack, but doesn't it take only a short distance for gravity to pull an object to it's top falling speed? That's why the old theory of dropping a penny off of a skyscraper and it would kill them, but in reality, if can't hurt anymore than if you dropped it off of something 30 feet high, because it can't accel. anymore. So even if you dropped something from 30,000, it would still only do so much damage, right? Sorry to hijack, jsut thought this was along the same lines. (only backwards )Crexrun

 

[outlawmws]

not trying to hijack, but doesn't it take only a short distance for gravity to pull an object to it's top falling speed? That's why the old theory of dropping a penny off of a skyscraper and it would kill them, but in reality, if can't hurt anymore than if you dropped it off of something 30 feet high, because it can't accel. anymore. So even if you dropped something from 30,000, it would still only do so much damage, right? Sorry to hijack, jsut thought this was along the same lines. (only backwards )Crexrun

Something small, traveling with sufficient speed, WILL kill someone. Years ago I read of Palestinians firing their AK47s (Celebrating?) in the air and several people were were killed, hit in the head with spent bullets completing a nearly vertical trajectory.

I wouldn't want to get hit by a penny off a tall skyscraper.

 

[RichPA]

not trying to hijack, but doesn't it take only a short distance for gravity to pull an object to it's top falling speed? That's why the old theory of dropping a penny off of a skyscraper and it would kill them, but in reality, if can't hurt anymore than if you dropped it off of something 30 feet high, because it can't accel. anymore. So even if you dropped something from 30,000, it would still only do so much damage, right? Sorry to hijack, jsut thought this was along the same lines. (only backwards )Crexrun

False. Gravity accelerates things until they hit, so the farther it falls, the faster it is going. So don't stand there and let somebody drop something off a skyscraper on to your head.

 

[luvvinvinyl]

Almost, Rich. Gravity causes a falling body to continue accelerating, until the downward force applied by gravity equals the resistance or 'drag' that the air provides, in the opposite direction, 'buoyancy'. The speed at which that occurs is the 'terminal velocity' of the object, to which EW referred. This velocity varies greatly, depending on the aerodynamics of the falling body. Skydivers can tell you just how much the TV of a falling human varies, given the attitude and position of the skydiver. Extend arms and legs outward, and wear a baggy jumpsuit, TV is slower. Curl up into a tight ball, ala the 'tuck position', and you will go faster. Adjust your attitude so that you are diving headfirst, with arms and legs held tight, to minimize the forwards surface area presented, and you will rocket downward. TV for a penny is much higher than for a feather. If you want to neglect the buoyancy of air, then your statement is true. The theoretical collapses, however, when you step out into the real world.

 

[markthefixer]

if it survived the trip through the atmosphere it would leave a crater.

Air friction can only bleed off some of the enormous energy.

Of course Terminal velocity exists, acceleration attempting to boost velocity beyond TV typically is mainfested in heating from air friction (ask ANY astronaut).

What do they call that pilots mantra? altitude, airspeed and brains... loose two and you are dead.

UNCLE

I wonder if I can go back and edit out everything that I have posted in this thread??

 

[EchoWars]

Almost, Rich. Gravity causes a falling body to continue accelerating, until the downward force applied by gravity equals the resistance or 'drag' that the air provides, in the opposite direction, 'buoyancy'. The speed at which that occurs is the 'terminal velocity' of the object, to which EW referred. This velocity varies greatly, depending on the aerodynamics of the falling body. Skydivers can tell you just how much the TV of a falling human varies, given the attitude and position of the skydiver. Extend arms and legs outward, and wear a baggy jumpsuit, TV is slower. Curl up into a tight ball, ala the 'tuck position', and you will go faster. Adjust your attitude so that you are diving headfirst, with arms and legs held tight, to minimize the forwards surface area presented, and you will rocket downward. TV for a penny is much higher than for a feather. If you want to neglect the buoyancy of air, then your statement is true. The theoretical collapses, however, when you step out into the real world.

Joe Kittinger, a native of Orlando, Florida, and eventually a Colonel in the Air Force, began flying aircraft in 1949. Kittinger qualified in practically all types of flying machines including hang gliders, hot air and gas balloons, propeller driven aircraft, and jet aircraft.

On August 16, 1960, he set three world records: the highest parachute jump (102,800 feet), the longest parachute free fall (4 minutes 36 seconds), and the first person to exceed the speed of sound without an aircraft or space vehicle (714 mph during free fall).

Very cool.

 

[RichPA]

Almost, Rich. Gravity causes a falling body to continue accelerating, until the downward force applied by gravity equals the resistance or 'drag' that the air provides, in the opposite direction, 'buoyancy'. The speed at which that occurs is the 'terminal velocity' of the object, to which EW referred. This velocity varies greatly, depending on the aerodynamics of the falling body. Skydivers can tell you just how much the TV of a falling human varies, given the attitude and position of the skydiver. Extend arms and legs outward, and wear a baggy jumpsuit, TV is slower. Curl up into a tight ball, ala the 'tuck position', and you will go faster. Adjust your attitude so that you are diving headfirst, with arms and legs held tight, to minimize the forwards surface area presented, and you will rocket downward. TV for a penny is much higher than for a feather. If you want to neglect the buoyancy of air, then your statement is true. The theoretical collapses, however, when you step out into the real world.

Yes, of course. This is why I try to avoid stepping out into the real world

 

[crexrun]

Sorry guys, not only did I hijack the thread, I was wrong to boot! Evidiently, I misread something about gravity, I knew about the air resistance, that's obvious, but I didn't realize that an object would keep accelerating. Learn something new every day. Thanks guys, sorry I switched topics, now back to regularly scheduled programming. Crexrun

 

[usedto]

I live in farm country, and I just waded through enough bullsh*t to fertilize an 80 acre field to get here.

So do I jump in a falling elevator or not?

 

[Lefty]

escape velocity

That means the speed in which one has to pick-up the mint vintage SX-1980 from under the pile of BPC in the rear of the Good Will Store, get it to the check-out, pay for it and get it in the car trunk before they figure out that they may have underpriced it at $29.95......

Lefty

 

[outlawmws]

escape velocity

That means the speed in which one has to pick-up the mint vintage SX-1980 from under the pile of BPC in the rear of the Good Will Store, get it to the check-out, pay for it and get it in the car trunk before they figure out that they may have underpriced it at $29.95......

Lefty

:lmao: best definition yet! :thmbsp:

 

[WhiteSE]

As i see it, you never escape the effects of gravity.....What happens is that the shuttle lets say, by travelling at such high speeds, is in a constant freefall on the other side of the horizon...

you can be in orbit and not be in outerspace, if you went fast enough,,but air friction would be a bitch.

Gravity is what keeps the shuttle in orbit,,,otherwise it would go straight into outer space...it still has 2 vectors..fwd and down..but it goes so fast that its always falling past the horison.