Help me analyze the situation of torque

  • Thread starter tukms
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In summary, the conversation discusses the confusion surrounding the conclusion in the textbook that net internal torque is equal to zero, which is similar to Newton's third law. The individual is questioning this conclusion and provides their own definition of torque as r x F. They also mention a specific case where this conclusion may not hold true. They request help in explaining this situation and express their appreciation in advance.
  • #1
tukms
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I have a confusion of a conclusion in the textbook ( I posted it in the attach file )

Net internal torque equals zero ( similarly to conclusion in the Newton’s third law ) but I myself reckon that torque is defined as
$rm{r \times F$
And maybe there occurs the case below :
$rm{F}}_{{\rm{21}}} {\rm{ = - F}}_{{\rm{12} $
But
$rm{r}}_{21} {\rm{F}}_{{\rm{21}}} \ne {\rm{r}}_{12} {\rm{ - F}}_{{\rm{12}$

Could someone help me analyze this situation , I think that the conclusion in textbook is true but it is still fuzzy for me
Thank you in advance
 

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  • #2
I only try to post Latex but no success :(

again
I have a confusion of a conclusion in the textbook ( I posted it in the attach file )

Net internal torque equals zero ( similarly to conclusion in the Newton’s third law ) but I myself reckon that torque is defined as
${\rm{r \times F}}$
And maybe there occurs the case below :
${\rm{F}}_{{\rm{21}}} {\rm{ = - F}}_{{\rm{12}}} $
But
${\rm{r}}_{21} {\rm{F}}_{{\rm{21}}} \ne {\rm{r}}_{12} {\rm{ - F}}_{{\rm{12}}} $

Could someone help me analyze this situation , I think that the conclusion in textbook is true but it is still fuzzy for me
Thank you in advance
 
  • #3
though I can't post Latex truly , i guess you would know my confusion , please answer me as soon as possible

thank you :)
 
  • #4
You must use [tex*] and [*/tex] (with out the *) on your latex code.
 
  • #5
welcome to pf!

hi tukms! welcome to pf! :smile:

(try using the X2 icon just above the Reply box :wink:)

the important point in your attachment is "we assume that these forces lie along the line of separation of each pair of particles" …

so if the internal forces are F12 and F21, at positions r1 and r2,

then the total moment (about any origin) is r1 x F12 + r2 x F21 = (r1 - r2) x F12

since r1 - r2 is parallel to F12, that comes to zero :wink:
 

Related to Help me analyze the situation of torque

1. What is torque and how is it defined?

Torque is a measure of the turning force applied to an object, which causes the object to rotate around an axis. It is defined as the product of the force applied and the distance from the axis of rotation to the point of application of the force.

2. Why is it important to analyze the situation of torque?

Analyzing the situation of torque is important because it allows us to understand the forces and moments acting on an object, which is crucial in engineering and physics applications. It also helps us to determine the stability and equilibrium of an object.

3. What factors affect the magnitude of torque?

The magnitude of torque is affected by the applied force, the distance from the axis of rotation, and the angle between the force and the lever arm. Additionally, the type of force (e.g. linear or rotational) and the properties of the object (e.g. mass, shape, and distribution of mass) can also affect the magnitude of torque.

4. How is torque different from force?

Force is a vector quantity that describes the push or pull on an object, while torque is a rotational force that causes an object to rotate around an axis. Force is applied to a specific point on an object, whereas torque is applied to an axis of rotation.

5. What are some real-world examples of torque?

Some examples of torque in everyday life include opening a door, tightening a bolt with a wrench, and using a lever to lift a heavy object. In engineering, torque is also important in designing machines and vehicles, such as the torque produced by an engine to rotate the wheels of a car.

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