Internal and external torques.

In summary, determining whether a torque on a system is internal or external before conserving angular momentum requires identifying the system and understanding its components. If the system is isolated, the sum of angular momenta will be conserved. However, if the system is not isolated, the angular momentum of the system plus any external factors will be conserved.
  • #1
transparent
19
0
How do I tell if a torque on a system is internal or external before conserving angular momentum? I know that if a force has its reactionary force in the system, then it is an internal force and we can conserve the linear momentum of the system. But I don't know how to recognize a reactionary torque. For example, if two rough rotating bodies (say cylinders) are brought into contact with each other, the torque experienced by them due to friction is different and hence the angular momentum cannot be conserved in this two-body system even though the forces are all internal.
 
Physics news on Phys.org
  • #2
It's simple enough. Before you set out figuring out what's internal and what's external, you have to spell out to yourself what your system is. In this case, if your system is either one of the cylinders, then the other cylinder is external to it and neither system's angular momentum will be conserved. If your system is both cylinders together and this system is isolated, then the sum of the angular momenta of the cylinders will be conserved throughout. When, because of friction, the surfaces in contact come to rest relative to each other, the two-cylinder system will rotate about an axis passing through its center of mass. If the two-cylinder system is not isolated, say because the cylinders spin about shafts that are firmly attached to the Earth, then the angular momentum of the two-cylinder system is not conserved. However, the angular momentum of the two-cylinder system plus Earth will be conserved. Do you see how it woks?
 

What is the difference between internal and external torques?

Internal torque refers to the force that is generated within a system, such as within a muscle when it contracts. External torque, on the other hand, refers to the force that is applied to a system from an outside source, such as gravity or an external force acting on a lever.

How do internal and external torques affect movement?

Internal and external torques work together to create movement in a system. The internal torque generated by muscles contracts and moves the bones, while external torques act as opposing forces to create resistance or assist in movement.

What factors influence the magnitude of internal and external torques?

The magnitude of internal and external torques is influenced by a variety of factors, such as the strength and coordination of muscles, the length and lever arms of bones, and the direction and magnitude of external forces acting on the system.

How do internal and external torques relate to joint stability?

Internal and external torques play a crucial role in joint stability. Internal torques help to stabilize joints by providing opposing forces to maintain joint position and prevent dislocation. External torques can also contribute to joint stability by providing resistance against forces that could cause joint injury.

How are internal and external torques measured and calculated?

Internal and external torques can be measured and calculated using the principles of torque, which takes into account the distance from the axis of rotation, the force applied, and the angle of application. Sophisticated equipment such as force plates and motion analysis systems can also be used to measure and calculate internal and external torques in biomechanical studies.

Similar threads

Replies
9
Views
1K
Replies
3
Views
1K
Replies
5
Views
1K
Replies
52
Views
2K
Replies
1
Views
600
Replies
40
Views
2K
Replies
36
Views
14K
Back
Top