champu 1 #1 December 10, 2003 This bit of terminology came up in an RSL thread in refernce to spinning malfunctions. It's really more of a semantic clarification on the physics than real news. If you get into a spin under canopy you'll notice yourself staring to feel very heavy in your harness. The reason for this is because objects like travelling in straight lines. To get them to travel in a circle, you have to constantly pull them towards the middle of the circle, and this is what your canopy is doing, pulling you toward the center of your spin. This is called a "centripetal" force (I attatched a little simplified drawing) When you cutaway you'll fly off in the direction of the little velocity arrow. What you won't do is fly away from the center of the circle as is suggested by saying there is some "cetrifugal" force. Quote Share this post Link to post Share on other sites
ripper0289 0 #2 December 10, 2003 Centripetal, centrifigal, feh, it's all just fancy names for inertia. " A centrifugal force is a force on an object that tends to move it away from a center of rotation and always results from the inertia of the object. Inertia is the property of an object proportional to mass that opposes acceleration. A centripetal force is a force on an object that tends to move it toward a center of rotation and can be a result of gravitation, electricity, or any other naturally occurring force." Quote Share this post Link to post Share on other sites
champu 1 #3 December 10, 2003 I am well aware that the sole reason this thread exists, is because I am a colossal nerd... what I was really getting at is that the acceleration you experience, or in other words the Gs you undergo are "centripetal" or directed towards the center of the rotation, and that's why you feel heavy in your harness. You'll have plenty of time to ponder the finer points of what just happened while you wonder around looking for your freebag Quote Share this post Link to post Share on other sites
FrogNog 1 #4 December 10, 2003 QuoteI am well aware that the sole reason this thread exists, is because I am a colossal nerd... I'm with you on this "being a nerd" issue. I have thus far resisted making a post explaining "breaks vs brakes" and "flare vs flair". (Your post itself is asking for "wonder vs wander" .) And don't even get me started on apostrophe abuse. -=-=-=-=- Pull. Quote Share this post Link to post Share on other sites
champu 1 #5 December 10, 2003 Quote(Your post itself is asking for "wonder vs wander" .)Ahh crap! Hmm, would you believe me if I told you I use a strange keyboard where "o" and "a" are adjacent and my finger slipped? And there's nothing wrong with a little flair in your flare, as long as you don't break a brake. Quote Share this post Link to post Share on other sites
Kennedy 0 #6 December 10, 2003 You realize that according to your drawing one would feel lighter? We're heavier because both forces apply. Centrifugal force makes your lines tight, centripetal makes you spin. Quote" A centrifugal force is a force on an object that tends to move it away from a center of rotation and always results from the inertia of the object. Inertia is the property of an object proportional to mass that opposes acceleration. A centripetal force is a force on an object that tends to move it toward a center of rotation and can be a result of gravitation, electricity, or any other naturally occurring force." Finely put. Where'd you get it?witty subliminal message Guard your honor, let your reputation fall where it will, and outlast the bastards. 1* Quote Share this post Link to post Share on other sites
happythoughts 0 #7 December 10, 2003 I keep picturing someone laying on the ground, explaining "...I couldn't cut away because of the centrifugal force and..." "It's centripetal, dammit." Quote Share this post Link to post Share on other sites
champu 1 #8 December 10, 2003 QuoteYou realize that according to your drawing one would feel lighter? We're heavier because both forces apply. Centrifugal force makes your lines tight, centripetal makes you spin.As I said, this is more semantic than anything. If you look at you in your harness, there's only one force applied, and that's towards the center of rotation, this unopposed force causes you to accelerate towards the center of the rotation, and makes you spin. If you want to argue that your harness is pushing on you, and you are pushing back on your harness (to prevent from moving relative to it), that's fine, but that force has nothing to do with rotation, that interaction takes place completely within the box in my drawing. /edited to add: "A centrifugal force is a force on an object that tends to move it away-" No no no, bad bad bad, wrong wrong wrong. Forces DO NOT move things, forces accelerate things. And yes, there is a big difference. Quote Share this post Link to post Share on other sites
Kennedy 0 #9 December 10, 2003 QuoteIf you look at you in your harness, there's only one force applied, and that's towards the center of rotation, this unopposed force causes you to accelerate towards the center of the rotation, and makes you spin. If you want to argue that your harness is pushing on you, and you are pushing back on your harness (to prevent from moving relative to it), that's fine, but that force has nothing to do with rotation, that interaction takes place completely within the box in my drawing. If there is only one force, you would move in the direction of that force, in this case towards the center. Without centrifugal force, you wouldn't spin. I understand centripetal makes you spin, but in your drawing it wouldn't work without centrifugal. The spin is the result of both forces acting. What you marked velocity is basically the tangent to the circle. You can't get that from a force driving towards the center.witty subliminal message Guard your honor, let your reputation fall where it will, and outlast the bastards. 1* Quote Share this post Link to post Share on other sites
champu 1 #10 December 10, 2003 I added it to my other post because I noticed it in that quote taken from wherever, but I'll emphasize it because it is just so huge. Forces do not move things. Forces accelerate things. If you are driving your car going 60mph (forwards), and slam on your brakes, you are applying a huge force on your car in the backwards direction, yet you will not move backwards. At any given moment in the spinning example you are travelling tangent to the circle. Inertia doesn't know or care that you are spinning. All it wants to do is keep you moving in that straight line. A constant force towards the center of the circle keeps changing your direction and makes you move in a circle. If the force is taken away (you chop) you will continue moving in a straight line, tangent to the circle. Quote Share this post Link to post Share on other sites
billvon 2,400 #11 December 10, 2003 >If there is only one force, you would move in the direction of that >force, in this case towards the center. You are constantly accelerating (moving) towards the center. You could swing around a point in space by firing a rocket towards the center, or you could attach a rope to the same point and swing around it. You feel the same force - a force accelerating you towards the center. Since it's unopposed, your velocity vector is constantly changing (i.e. you are accelerating towards the center) but since you keep turning you never actually go very far. Quote Share this post Link to post Share on other sites
sdgregory 0 #12 December 10, 2003 Thank God! I am so glad I am not the only nerd on this site. I have been restraining myself considerably every time I see a physics error or a spelling error or, for that matter, a grammar error. Thank God there is not much math going on here or I would be sitting in a corner talking to myself. "2 plus 2 is 4! 2 plus 2 is 4!" P.S. I love the apostrophe abuse cartoon. Quote Share this post Link to post Share on other sites
wallygator 0 #13 December 10, 2003 what do you do to break out of a spin if its centrepetal or centirfugal, i had many answers to this question when asked and none of the answers seemed right.. Please explain recovering procedures and what not to do in this situation. Jah guide and protect -------------------------------------------------- who Jah bless Let no man curse. Quote Share this post Link to post Share on other sites
pilotdave 0 #14 December 10, 2003 QuoteYou realize that according to your drawing one would feel lighter? We're heavier because both forces apply. Centrifugal force makes your lines tight, centripetal makes you spin. Nope... I'm not gonna draw it but picture this: you're standing in an elevator. The elevator puts an upward force on your body. You feel heavier, not lighter, as you accelerate upwards. It's the same situation here. You are ACCELERATING toward the center of the circle. You are MOVING tangential to the circle. Centripetal force is the force that keeps you from flying off the circle. In other words, it points inward toward the center of the circle. If that force was to suddenly disappear, you will lose your acceleration toward the center of the circle and therefore continue to move in whatever direction you were already moving in... tangential to the circle. One more example... picture a satellite orbiting earth. There's plenty of gravity up there. It's not just floating in a weightless environment. So it's in freefall. It's accelerating toward earth at somewhere around 32 feet/sec^2 (I dunno what the actual number at that altitude would be, but it's not a whole lot lower than on the surface). So if it's accelerating downward, why isn't it falling out of orbit? Horizontal (tangential) speed is the answer. The only real force on the satellite is gravity, which obviously points straight toward the center of the earth (or at least close to it for those that are going to say the earths gravitational center isn't in the geometric center Dave Quote Share this post Link to post Share on other sites
JumpCrazy 0 #15 December 10, 2003 edit to say: pilot dave posted the same thing while I was typing this. oh well. There's no such thing as centrifugal force. It's just something that people make up to help them understand centripital force. If you think about it, this is true. What could possibly be pulling you away from the canopy when you are spinning? nothing. You body has the tendancy to travel in a line perpendicular to the direction of centripital force. This causes the feeling of a downward force (centrifugal) that isn't actrually thereFlying Hellfish #470 Quote Share this post Link to post Share on other sites
kallend 1,625 #16 December 10, 2003 Quoteedit to say: pilot dave posted the same thing while I was typing this. oh well. There's no such thing as centrifugal force. It's just something that people make up to help them understand centripital force. If you think about it, this is true. What could possibly be pulling you away from the canopy when you are spinning? nothing. You body has the tendancy to travel in a line perpendicular to the direction of centripital force. This causes the feeling of a downward force (centrifugal) that isn't actrually there Newton's 3rd law. For every centripetal force, there is an equal and opposite centrifugal force. (OK, I made that up) Centrifugal force is a pseudo or virtual force. It is an apparent force that an observer in a rotating frame of reference detects to square his/her observations with Newton's laws, that would not be apparent to an observer in a non rotating frame of reference. Coriolis force is similarly a pseudo force.... 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
samhussey 0 #17 December 10, 2003 You're right, there is no centrifugal force. You feel heavier because the canopy is keeping you in the 'circle' whilst your body is trying to go in a straight line. The force you feel is not pushing you outwards, its stopping you from going outwards. There is no force pushing you outwards. Edited to add: newtons third law? that merely states that since you are exerting force on the harness, the harness is exerting force on you. Once this law is broken, either you go through the harness, or the harness goes through you. Quote Share this post Link to post Share on other sites
bmcd308 0 #18 December 10, 2003 >>If there is only one force, you would move in the direction of that force, in this case towards the center. << Movement and acceleration are different. You are accelerating toward the center because of the force. You are moving around in a circle because the direction of your velocity keeps changing as a result of the acceleration toward the center. ---------------------------------- www.jumpelvis.com Quote Share this post Link to post Share on other sites
BikerBabe 0 #19 December 10, 2003 LOL, my dad the physicist used to yell at me in high school when I was taking HS physics: "There's no such thing as centrifugal force!!!!!!!!!" I'm a nerd, too, so when I hear the term centrifugal force used incorrectly, I grind my teeth. I usually don't try to explain, because the people using it incorrectly probably wouldn't understand, anyway. I'm also a grammar nazi, so I combine the best of both nerd worlds! I wish I had a scanner so I could draw a picture for people...it's so much easier to understand if you can see it.Never meddle in the affairs of dragons, for you are crunchy and taste good with ketchup! Quote Share this post Link to post Share on other sites
kallend 1,625 #20 December 10, 2003 QuoteLOL, my dad the physicist used to yell at me in high school when I was taking HS physics: "There's no such thing as centrifugal force!!!!!!!!!" I'm a nerd, too, so when I hear the term centrifugal force used incorrectly, I grind my teeth. I usually don't try to explain, because the people using it incorrectly probably wouldn't understand, anyway. I'm also a grammar nazi, so I combine the best of both nerd worlds! I wish I had a scanner so I could draw a picture for people...it's so much easier to understand if you can see it. The Force may be with us, but Newton says that every action has an equal and opposite reaction. SO what do you call the equal but opposite force to the centripetal force?... 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
bmcd308 0 #21 December 10, 2003 tension? ---------------------------------- www.jumpelvis.com Quote Share this post Link to post Share on other sites
rehmwa 2 #22 December 10, 2003 Milk Duds? ... 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
champu 1 #23 December 10, 2003 Quotebut Newton says that every action has an equal and opposite reaction. SO what do you call the equal but opposite force to the centripetal force?The centripetal force to keep you spinning is provided by the lift of your improperly oriented canopy. The equal and opposite force is on the air molecules passing over the lower surface of the wing. (Bernoulli's Principle) Quote Share this post Link to post Share on other sites
champu 1 #24 December 10, 2003 QuoteI wish I had a scanner so I could draw a picture for people...it's so much easier to understand if you can see it.I thought the picture I drew and attatched to the original post made it pretty clear... Quote Share this post Link to post Share on other sites
rehmwa 2 #25 December 10, 2003 That's why we used to draw a box around the system to draw force diagrams or you get into these discussions as follows: force of air on wing = force of wing on air but force of body on harness = force of harness on body but what about the harness vs parachute forces.... Then is it the force of the air on the body equal. That doesn't make sense - and so on and so forth. it can be fun to do to those who aren't mathematically inclined... ... 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
