Question about torque and center of mass

Click For Summary
SUMMARY

This discussion focuses on the concepts of torque and center of mass in rigid body dynamics. Torque is defined as τ = r × F, where r represents the position vector and F is the force applied. It is clarified that torque can be calculated regardless of whether r is fixed in magnitude, as long as the rigid body is rotating about a fixed point or axis. Additionally, the gravitational forces acting on a rigid body can be simplified to a single resultant force acting at the center of mass, which is crucial for analyzing the system's motion.

PREREQUISITES
  • Understanding of basic physics concepts, specifically torque and rotational motion.
  • Familiarity with vector mathematics, including cross products.
  • Knowledge of rigid body dynamics and the concept of center of mass.
  • Basic grasp of gravitational forces and their effects on objects.
NEXT STEPS
  • Study the mathematical derivation of torque in various contexts.
  • Learn about the implications of variable radius in torque calculations.
  • Explore the concept of center of mass in different shapes and systems.
  • Investigate the role of torque in real-world applications, such as machinery and vehicles.
USEFUL FOR

This discussion is beneficial for physics students, educators, and anyone interested in understanding the principles of torque and center of mass in rigid body dynamics.

AGC
Messages
2
Reaction score
0
I am a beginner and this is my first post.

We know torque ## \vec T = \vec r × \vec F ## Now, should r be fixed in magnitude? I mean can I calculate torque only if the particle is rotating at a fixed distance around a fixed axis? I am having this idea because torque is explained (from where I read) using an analogy with doors.

Second question. I read that generally a system of forces acting on a rigid body can not be reduced to a single force equal to the vector sum of the forces. Then I get confused because in case of weight, we replace gravitational forces on each particle of a rigid body with a resultant force through the center of mass.
Will someone please explain?
 
Physics news on Phys.org
about your first question , your question is how can we deal with torque when r is variable 'not constant in magnitude' ?
 
Last edited:
About your second question , [As I know] we treat the rigid body as a particle-like object so that the gravitational force will act only on its center of mass.
 
Maged Saeed said:
about your first question , your question is how can we deal with work when r is variable not constant 'in magnitude' ?
I think my first question was not clear enough. I asked if the concept of torque is applicable only if the particle (or body) is rotating about an axis? And should it rotate in a fixed radius? Sorry if the question is of very intro level.
 
No , [As far I know] The concept of torque can be applied if the rigid body is rotating about either a fixed point or a fixed axis , where the point 'similarly to the axis of rotation ' is allocated on an axis vertical to the xy-plane.
 
See this vedio:
 

Similar threads

Undergrad Properties of angular momentum
  • · Replies 6 ·
Replies
6
Views
776
Graduate Torque about center of mass due to Coriolis force, is it 0?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Effects of External Torques on the Angular Momentum of Asymmetric Bodies
  • · Replies 3 ·
Replies
3
Views
2K
High School Non-physicist needs your help torquing a nut!
  • · Replies 9 ·
Replies
9
Views
1K
Undergrad Off center torque applied to a rotating body
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad A Question About the Physical Explanation Behind Torque
  • · Replies 8 ·
Replies
8
Views
2K
Undergrad What makes a door move, the torque or the force or both?
  • · Replies 52 ·
2
Replies
52
Views
7K
Undergrad Where is the centripetal force acting on mass M?
  • · Replies 21 ·
Replies
21
Views
2K
Undergrad Trying to calculate the net force/torque of a rock climber on a wall
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Torque required from powered roller to rotate cylinder
  • · Replies 19 ·
Replies
19
Views
2K