Timeline for Do objects rotate around the torque vector or its center?
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17 events
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| Jan 28, 2020 at 17:46 | comment | added | John Alexiou | @ViniciusACP - In real life it is very difficult to apply a pure torque. In the example you mentioned the net force must be such that the center of mass accelerates. In fact playing with a pencil in your hands, you are fixing the rotation axis to be between your fingers and letting the contact force be whatever it need to be as such. It is really hard to impose a torque without applying a force. The best example I can think of is the magnetic stirrers they use in chemistry labs. Also look at this. The center of mass moves in a straight line. | |
| Jan 28, 2020 at 16:25 | comment | added | Vinicius ACP | @ja72 I understand, and you are right. But what I'm trying to do is to gain an intuition (mathematically it makes sense to me) about the statement of your answer: "A pure torque any point on the body (with no net force) will purely rotate a rigid body about its center of mass." The pencil and sphere are just examples to illustrate my doubt about this statement. | |
| Jan 28, 2020 at 16:12 | comment | added | John Alexiou | @ViniciusACP - comments isn't really the place to answer a question or prove a case. If you have doubts about the center of rotation for a particular situation please ask a new question in this site. But there are a lot of similar questions already posted. You just have to search for them. | |
| Jan 28, 2020 at 13:43 | comment | added | Vinicius ACP | @ja72 Even in this case it rotates around the center of mass!? That's what I'm not understanding. If i take a pencil, for example, and apply a couple near one of its ends, the rotation produced is apparently around an axis that pass through the midpoint of force application points and not the center of mass... | |
| Jan 28, 2020 at 12:51 | comment | added | John Alexiou | A pure torque is when the net torque isn't zero at the center of mass, but the net force is. This can happen with 2 or more forces acting on a body. A pure torque has the same measured torque value about all points on the body. In the semisphere case, the body does rotate about the center of mass. That is to say the center of mass will not move (since there is no net force acting on it). | |
| Jan 28, 2020 at 9:59 | comment | added | Vinicius ACP | I've read in a book the following: "The only condition in which a pure rotation may occur is that of a 'conjugate system' (two simultaneous forces, with the same torque: equal magnitudes and opposite directions, with diametrically opposed points of application)" | |
| Jan 28, 2020 at 9:59 | comment | added | Vinicius ACP | I'm thinking in the situation of a sphere with the couple applied in the same hemisphere, i.e., not diametrically opposed forces. In this case we have no net force, but wouldn't the rigid body rotate about an axis that is not in the center of mass? | |
| Jan 28, 2020 at 9:58 | comment | added | Vinicius ACP | @ja72 When you say pure torque, does it imply that the couple associated with it is formed with forces applied in diametrically opposed points? | |
| Aug 27, 2018 at 12:25 | comment | added | John Alexiou | A pure torque cannot cause a net force. Unless you are talking about reaction forces. A pined body under a pure torque will have a net force because the com can only rotate about the pivot. The rule is, forces => motion of com, torques => motion about com. | |
| Aug 27, 2018 at 10:25 | comment | added | Scáthach | What if the torque at any point of the body is causing a net force.... Will it cause both rotation and translation of com I am studying rotation and this point is bothering me a lot so can you help me with this | |
| Apr 29, 2017 at 1:42 | history | edited | John Alexiou | CC BY-SA 3.0 |
center of gravity -> center of mass
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| Apr 13, 2017 at 12:39 | history | edited | CommunityBot |
replaced http://physics.stackexchange.com/ with https://physics.stackexchange.com/
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| Oct 18, 2013 at 14:53 | vote | accept | dfg | ||
| Oct 17, 2013 at 19:40 | history | edited | John Alexiou | CC BY-SA 3.0 |
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| Oct 17, 2013 at 19:28 | history | edited | John Alexiou | CC BY-SA 3.0 |
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| Oct 17, 2013 at 15:11 | history | edited | John Alexiou | CC BY-SA 3.0 |
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| Oct 17, 2013 at 14:02 | history | answered | John Alexiou | CC BY-SA 3.0 |