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| PlainName:
--- Quote ---Not quite sure you read what I wrote at point b) --- End quote --- I am very sure you didn't read (or understand) my point about slip. Have you never wondered how a clutch works? You can have slip and yet still transfer power - it is not all or nothing. Thus your statement that " If slip is allowed acceleration will be zero if the right wheel slips" is one extreme. It could slip and still allow acceleration. |
| PlainName:
--- Quote from: cbutlera on February 06, 2023, 11:50:13 pm ---[...] --- End quote --- Apologies for butting in. Don't know what came over me, and you were doing a far better job. I shall leave you to it :) |
| electrodacus:
--- Quote from: cbutlera on February 06, 2023, 11:50:13 pm --- You have agreed that the two horizontal forces that act on the vehicle are not Newton's third law force pairs, and so they do not have to be equal and opposite in all circumstances. When they are not equal and opposite, the vehicle will be subject to a net force. This net force must cause the vehicle to accelerate, this is Newton's second law. Are you claiming that this law should include the proviso that it is only true if something slips? --- End quote --- Sorry if I was not clear. In my diagrams F1 = F2 and is Newton's 3'rd law that applies there. There can not be motion without slip in any of my diagrams. If you look closely at how the belt is connected you will understand that this is a "locked box". Meaning it can only move if the left wheel slips. If the right wheel slips then only the treadmill surface moves the "vehicle/gearbox" will not move relative to ground. Te examples given for third law almost always involve gravity and that is not a requirement for Newton's 3'rd law thus the failing in understanding what the 3'rd law is about. Say gear ratio is 2:1 in case A you can consider any type of reference frame you want. Will F2 = 2 * F1 ? The answer is clear no and F1 = F2 in a non accelerating frame or F1 = F2 + m*a in an accelerating frame. Thus F1 is always equal or larger than F2 and never the other way around. When both energy storage and stick slip hysteresis are involved the discussion is very different but those two are not provided in the simple example A. |
| cbutlera:
--- Quote from: electrodacus on February 07, 2023, 12:19:28 am --- --- Quote from: cbutlera on February 06, 2023, 11:50:13 pm --- You have agreed that the two horizontal forces that act on the vehicle are not Newton's third law force pairs, and so they do not have to be equal and opposite in all circumstances. When they are not equal and opposite, the vehicle will be subject to a net force. This net force must cause the vehicle to accelerate, this is Newton's second law. Are you claiming that this law should include the proviso that it is only true if something slips? --- End quote --- Sorry if I was not clear. In my diagrams F1 = F2 and is Newton's 3'rd law that applies there. ... --- End quote --- But F1 and F2 are not a Newton’s third law force pair. Carefully read again the paragraph from page 5 of the paper regarding the N2-NF misconception. It addresses precisely this issue. Have you now decided that you do not agree with the arguments presented in this paper? “Consider an object in static equilibrium, under the influence of just two forces. In the Newton’s Second Law – Net Force” (N2-NF) misconception, students note that the two forces must sum to zero (a correct application of the Second Law) and hence the two forces must be equal in magnitude and opposite in direction (also correct, as a direct mathematical result of the first statement), and thus are a Third Law force-pair (incorrect). This reasoning is similar to the (il)logical sequence, “All cats have four legs; my dog has four legs; therefore, my dog is a cat”. While a Third Law force-pair are equal in magnitude and opposite in direction, not all forces which are equal in magnitude and opposite in direction are a Third Law pair. This subtlety is often lost on novice students; but the mental model which arises from the flawed sequence of reasoning is strong and resistant to instruction (Wilson & Low, 2015)." |
| electrodacus:
--- Quote from: cbutlera on February 07, 2023, 12:39:20 am --- But F1 and F2 are not a Newton’s third law force pair. Carefully read again the paragraph from page 5 of the paper regarding the N2-NF misconception. It addresses precisely this issue. Have you now decided that you do not agree with the arguments presented in this paper? --- End quote --- What will you say that F1 = F2 are a consequence of if not Netwonds 3'rd law ? Or are you saying F1 is not equal with F2 in my examples ? If so please explain how F1 can be different from F2. What is the mechanism to allow that ? And to be clear what I claim is the same as what is observed in a real world test. If F1 is less than what is needed for any of the wheels to slip then F1 = F2 If F1 is large enough that a wheel can slip it depends on which one slips. -if is the one on the right F1 = F2 (vehicle is not moving) -if is the one on the left F1 = F2 + (m * a) (vehicle moves to the left in the direction the applied F1 is pointing) video proof: https://odysee.com/@dacustemp:8/stick-slip-removed-from-front-wheels:0 In order for the vehicle to move in the opposite direction of applied force as seen in this other video both energy storage and stick slip hysteresis needs to be involved https://odysee.com/@dacustemp:8/wheel-cart-energy-storage-slow:8 In this last case forces are not constant over time. Initial phase F1 = F2 and increasing in value as only right wheel spins stretching the belt (storing potential elastic energy). At some point force is large enough for the right wheel to slip and in that moment the stored elastic energy is converted into kinetic energy. The front wheel will stik (at a different force than it needed to start slipping thus the hysteresis) and the process will repeat multiple times per second (smaller the energy storage the faster the cycle of charge/discharge). Again prove is in the video. You can build your own mechanism and you will observe the exact same thing. It should not be needed to build the experiment if you understand physics including newton's 3'rd law as without energy storage an object will not move in the opposite direction of applied force. |
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