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inv
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Why should it ? The wire also exerts an upward force on the block, counteracting the torque from the tangential component. Still need a calculation to show if one of the two changes wins.inv said:"Did the block of wood successfully act as a lever directing the force perpendicular to the arm of the machine, as the red arrow indicates?"
Another thinner block of wood screwed to the machine arm, as shown.BvU said:What is the block of wood attached to ?
It has to be attached to something at its end, so yes.sophiecentaur said:This "arm" has to be a lever, doesn't it?
I think there's no difference to the perpendicular force vector to the arm, what do you mean, maybe a picture can explain better?CWatters said:I think the short answer is no! The block does not achieve the desired effect if it is fixed to the arm.
As proof, consider what happens if the round pulley is moved up and to the right so that it's at the pivot point of the arm.
inv said:I think there's no difference to the perpendicular force vector to the arm, what do you mean, maybe a picture can explain better?
The force on the string is at right angles but what about the force of the block on the arm, too? At the corner where the string bends around the block, there will be another force component that cannot be ignored. You cannot just pick a force that you fancy and use only that force in your conclusions.A.T. said:The force from the string at the red dot is 90° to the arm, if the string is 90° to the arm.
Merlin3189 said:I have to agree with Cwatters. I can't see why people are making such a meal of this.
IF the string and block are smooth (ie. frictionless) then the tension in the string at the red dot is the same as in the rest of the string. It will behave as if it were a pulley on a block attached to the arm.
BUT there will still be the additional forces on the block being transferred to the arm. So it will not behave like the *pulley on the left.
Practically it will not be frictionless, so it doesn't make sense to think of it as a pulley.
IMO, all the unnecessary calculations would yield the same results whether it was a rough block attached to the arm or a smooth pulley (of very small diameter!) attached to the arm.
Why don't you just get rid of the bits and pieces and tie the string to the arm, or to a nice solid extension if you need to offset the attachment?
sophiecentaur said:The question has not been defined fully enough for a proper answer. That is one of the problems here; we have to make assumptions where the information has been omitted.
If you replace the corner of that block with a tiny pulley, it would make no difference to the force that the deflected string exerts on the 'arm'. The force on the arm is just the tension in the string times the sine of the angle between the string and the arm (the component of the tension at right angles to the arm). Whether you follow my original assumption of the arm being a lever or not, the final answer is the same.
It is important [NOT! Edit] to rely on any 'gut' reaction that one has, due to the way the picture has been drawn and to get to the basics of it - that is, a string pulling at an arm at an angle. I was assuming that the arm is a lever because it's more convenient and because it is very unlikely that the arm would be attached rigidly to 'something' without being intended to turn it. In any case, whether intentional or not, there will be a torque on the arm. Unless the object it is attached to is shaped so that its cm is actually behind the contact point of the string (i.e. somewhere outside the picture, to the right) then there is a torque, by definition.
It is rather disappointing that this question about such a concrete bit of Mechanics seems to be treated in such an arm waving way. Given the facts, there is only one solution.
I think it'll pull up on the pivot and destroy it.CWatters said:OK try this diagram. The rope is in red.
View attachment 99588
To the right. What's the reason for these 2 results?CWatters said:If you think the force on the arm is still to the left (causing it to rotate clockwise) then try this one. Which way will this one rotate?
View attachment 99591
sophiecentaur said:The force on the string is at right angles but what about the force of the block on the arm, too? At the corner where the string bends around the block, there will be another force component that cannot be ignored. You cannot just pick a force that you fancy and use only that force in your conclusions.
The corner (or the pulley you replace it with) is pushing the string to one side (to make it kinked). So there has to be an extra force on it, in addition to the 'tension' in the string from the corner to the red spot. That extra force is transmitted to the arm. The resultant of this force and the string tension will be the same as the force from the long piece of string (i.e. 100N) The direction will necessarily be in the direction of the string. Because the angle of the string is different (with the block in place) the force, normal to the arm, will be different and the torque will be different.inv said:Am I right to say you're saying the block's friction is causing the same force vector on it on the arm? If so, if the block's replaced with a pulley, it still causes the same "force vector" on the arm, unless it's separate from that arm, ie anywhere from its pivot, even while still on the machine?
Here we are again suffering from the fact that the OP was not precise enough. I am assuming we are trying to turn the arm so the relevant force is the force normal to the arm. Any other component is acting through the pivot and will have no effect. And... if we are interested in the torque, the relevant quantities are the Force (tension) and the Perpendicular distance between the pivot (hidden) and the string. If you are confused by the way the thread is going then don't blame me. Blame the OP. Perhaps we could benefit from a properly modified diagram?inv said:But is the Force Vector at the point perpendicular to the arm?
A pulley force vector is a type of force that acts on an object due to the tension in a rope or cable that is wrapped around a pulley. It is typically used to change the direction of a force or to lift an object.
A pulley can reduce the amount of force needed to lift a 10kg weight by spreading the load over multiple ropes or cables. The mechanical advantage of the pulley system can also be increased by adding more pulleys, further reducing the force needed to lift the weight.
Friction is a force that acts in the opposite direction of motion between two surfaces in contact. In the case of a pulley system, friction can occur between the rope or cable and the pulley. This friction can affect the amount of force needed to lift the 10kg weight, as some of the force will be lost to overcoming the friction.
To check the amount of friction on a 10kg weight in a pulley system, we can use a spring scale or force meter to measure the force needed to lift the weight. By comparing this force to the expected force based on the weight and mechanical advantage of the pulley system, we can determine the amount of friction present.
The amount of friction on a 10kg weight in a pulley system can be affected by several factors, including the type and condition of the rope or cable, the material and condition of the pulley, and the angle of the rope or cable as it wraps around the pulley. Additionally, external factors such as temperature and humidity can also affect the amount of friction present.