kjundvr 0 #1 March 1, 2005 A physics question. This has been bugging me for some time. I have seen on the market skydiver weight belts and they say that you would use them to equalize your fall rate to another person. Well it happens that a man a few centuries ago said that objects of differing masses would fall at the same rate. So why the need for the weight, where in any physics calculations does mass/weight have anything to do with you decent rate? Could someone possibly take a stab at explaining this to me? PS hope this makes sence Quote Share this post Link to post Share on other sites
Tink1717 2 #2 March 1, 2005 The physics are correct if you jump in a vacuum. The addition of weights simply makes it easier to equalize fall rates of two or more people who present the same weight but more or less surface area to the air that the body is moving through. In other words, it has to do with aerodynamic forces in addition to gravitational forces.Skydivers don't knock on Death's door. They ring the bell and runaway... It really pisses him off. -The World Famous Tink. (I never heard of you either!!) AA #2069 ASA#33 POPS#8808 Swooo 1717 Quote Share this post Link to post Share on other sites
freakflyer9999 1 #3 March 1, 2005 Drop a penny and a sheet of paper at the same time. Which one hits the floor first? Now strap on some weight to the sheet of paper and drop the two simultaneously. You might have to experiment with a couple of different weights, but you should be able to find a weight that makes both items hit the floor at the same time. Quote Share this post Link to post Share on other sites
mark 107 #4 March 1, 2005 QuoteThe physics are correct if you jump in a vacuum. Doesn't that just make your blood boil! Mark Quote Share this post Link to post Share on other sites
sight_burner 0 #5 March 1, 2005 well common sense. would a sheet of paper fall faster than a pen! would a 100 pound girl fall slower than her 190 pound coach? it's all about drag less weight more float. More weight less float and better penetration and speed. So they use weights for say the 100 pound girl to fall at the same rate as her coach or the coach would thro on a larger suit to throw out more drag so he to becomes as floaty as the student. I.E you get more air time in a tony suit or a wing suit. I don't care about fame I just want people to know my name qote ( Andrew Cebuhar) the thread is dead Quote Share this post Link to post Share on other sites
kjundvr 0 #6 March 1, 2005 Thanks that makes alot of sense. I figured that it had to do with arodynamic forces rather than just gravity Quote Share this post Link to post Share on other sites
happythoughts 0 #7 March 1, 2005 A packed parachute and an unpacked parachute weigh exactly the same, don't they? Why don't they fall the same? Quote Share this post Link to post Share on other sites
KrisFlyZ 0 #8 March 1, 2005 QuoteQuoteThe physics are correct if you jump in a vacuum. Doesn't that just make your blood boil! Mark LOL. My high school physics teacher used to say "This is fairy tale physics but you need to be able to grasp these principles first before moving on......." The physics in engineering school is closer to reality. Kris. Quote Share this post Link to post Share on other sites
larsrulz 0 #9 March 1, 2005 QuoteLOL. My high school physics teacher used to say "This is fairy tale physics but you need to be able to grasp these principles first before moving on......." The physics in engineering school is closer to reality. Kris. I don't know about that....I still have graduate level engineering courses that have us use spherical cows! I got a strong urge to fly, but I got no where to fly to. -PF Quote Share this post Link to post Share on other sites
AggieDave 6 #10 March 1, 2005 Ha! I went to school at one of the top engineering schools in the country. Freshmen physics still started out with a sphirical horse in a vacum...hell, there was even a question pertaining to a 2 diminsional box to make it slightly easy to do the equations.--"When I die, may I be surrounded by scattered chrome and burning gasoline." Quote Share this post Link to post Share on other sites
billvon 2,991 #11 March 1, 2005 >I still have graduate level engineering courses that have us use spherical cows! I've seen some pretty fat cows. Quote Share this post Link to post Share on other sites
bodypilot1 0 #12 March 1, 2005 QuoteA packed parachute and an unpacked parachute weigh exactly the same, don't they? Not if the packer leaves all the gravel in it from the last looser that jumped it! Funny how it always hits you on the top of the helmet after falling out of the nose of the canopy. Some idiots need to learn how to pick up a canopy.... Keepin' it safe! Edwww.WestCoastWingsuits.com www.PrecisionSkydiving.com Quote Share this post Link to post Share on other sites
skylee_pinoy 0 #13 March 1, 2005 QuoteThe physics are correct if you jump in a vacuum i second that... Quote Share this post Link to post Share on other sites
airtwardo 7 #14 March 1, 2005 Quote Drop a penny *** Like I have all this money to just THROW around! /\ ~ If you choke a Smurf, what color does it turn? ~ Quote Share this post Link to post Share on other sites
cbennettjr 0 #15 March 1, 2005 I still can't get over how many physics classes in college still teach centrifugal force. Um hello! Ain't no such thing! Quote Share this post Link to post Share on other sites
billvon 2,991 #16 March 1, 2005 > I still can't get over how many physics classes in college still >teach centrifugal force. Um hello! Ain't no such thing! It's like teaching normal force. It is a theoretical force which has a lot of utility in physics. It is quite 'real' in that it can be experienced, can be quantified etc even if it's just plain old inertia in a rotating frame of reference. Quote Share this post Link to post Share on other sites
rehmwa 2 #17 March 1, 2005 QuoteQuoteThe physics are correct if you jump in a vacuum. Doesn't that just make your blood boil! Mark That's funny in at least 3 different ways. ... Driving is a one dimensional activity - a monkey can do it - being proud of your driving abilities is like being proud of being able to put on pants Quote Share this post Link to post Share on other sites
darkwing 5 #18 March 1, 2005 QuoteI still can't get over how many physics classes in college still teach centrifugal force. Um hello! Ain't no such thing! I teach physics at a major producer of undergraduate physics majors, and we are always wondering where the students gets this stuff about "centrifugal" force. They certainly don't get it from any college physicist I know of. We blame the high schools. -- Jeff My Skydiving History Quote Share this post Link to post Share on other sites
Avion 0 #19 March 1, 2005 What do you mean centrifugal force is make believe. It's what pulls a string tight when someone twirls around a weight tied to it. Eveybody knows that, its just common sense Quote Share this post Link to post Share on other sites
kallend 2,026 #20 March 1, 2005 QuoteQuoteI still can't get over how many physics classes in college still teach centrifugal force. Um hello! Ain't no such thing! I teach physics at a major producer of undergraduate physics majors, and we are always wondering where the students gets this stuff about "centrifugal" force. They certainly don't get it from any college physicist I know of. We blame the high schools. It's the force centrifuges produce. Who ever heard of isotope separation in a centripete?... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
cbennettjr 0 #21 March 2, 2005 It doesn't pull the string tight by pulling OUT or away from center as centrifugal implies. The mass wants to move in a strait line moving FORWARD at 90 degrees to the axis. Try centripetal not centrifugal. It's what causes planets to orbit one another. Real simple physics. Quote Share this post Link to post Share on other sites
kallend 2,026 #22 March 2, 2005 QuoteIt doesn't pull the string tight by pulling OUT or away from center as centrifugal implies. The mass wants to move in a strait line moving FORWARD at 90 degrees to the axis. Try centripetal not centrifugal. It's what causes planets to orbit one another. Real simple physics. If I whirl an object around on a string, there is most definitely a measurable outwardly directed force on the anchor point of the string, as well as a measurable tension in the string. Any force measuring device, such as a load cell, is capable of recording it. Newton's 3rd law requires that it exist as a reaction to the centripetal force acting on the object moving in a circle. Calling it "centrifugal" is as good a name as any. Living in a rotating reference frame is a fact of life.... The only sure way to survive a canopy collision is not to have one. Quote Share this post Link to post Share on other sites
happythoughts 0 #23 March 2, 2005 QuoteIf I whirl an object around on a string So how's that Stiletto flyin' these days. By the end of this thread, perhaps someone can teach us some physics. Quote Share this post Link to post Share on other sites
Conundrum 1 #24 March 3, 2005 An object which is falling through the atmosphere is subjected to two external forces. One force is the gravitational force, expressed as the weight of the object. The other force is the air resistance, or drag of the object. The magnitude of terminal velocity depends on the weight of the falling body. For a heavy object, the terminal velocity is generally greater than a light object. This is because air resistance is proportional to the falling body's velocity squared. For an object to experience terminal velocity, air resistance must balance weight. An example that shows this phenomenon was the classic illustration of a rock and a feather being dropped simultaneously. In a vacuum with zero air resistance, these two objects will experience the same acceleration. But on the earth this is not true. Air resistance will equal weight more quickly for the feather than it would for the rock. Thus the rock would accelerate longer and experience a terminal velocity greater than the feather. The maximum velocity an object can reach while falling through the air is called the "terminal velocity". As something falls though air, there is an upward force on it due to the air itself (called air resistance). The size of this force gets larger as the speed of the falling object increases. Eventually, when the speed of the falling object is big enough, the upward force due to the air will equal the downward force due to gravity. When this happens the object won't speed up any more, and will just keep falling with the same speed (the terminal velocity). Quote Share this post Link to post Share on other sites
darkwing 5 #25 March 3, 2005 QuoteIf I whirl an object around on a string, there is most definitely a measurable outwardly directed force on the anchor point of the string, as well as a measurable tension in the string. Any force measuring device, such as a load cell, is capable of recording it. Newton's 3rd law requires that it exist as a reaction to the centripetal force acting on the object moving in a circle. Calling it "centrifugal" is as good a name as any. I don't disagree with you, but as you correctly point out, that outward force is on the anchor point in the center, and most people who use the term "centrifugal" apply it to the object that is rotating. -- Jeff My Skydiving History Quote Share this post Link to post Share on other sites
