Centripetal/Centrifugal Force and Moment of Inertia

Click For Summary

Discussion Overview

The discussion revolves around the dynamics of a forklift carrying a pallet with a box, specifically focusing on the conditions under which the box will tip over while navigating a turn. Participants explore the concepts of centripetal and centrifugal forces, moment of inertia, and the calculations required to determine tipping angles and forces involved.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant outlines a scenario involving a forklift and a box on a pallet, detailing assumptions about the system's rigidity and the center of gravity (CoG).
  • Another participant suggests that the tipping point occurs when the torque from the centripetal force exceeds the torque from gravity about the tipping corner.
  • A later reply discusses the possibility of the box returning to an upright position if the forklift slows down before the CoG passes the tipping point, emphasizing the need for quick action.
  • One participant provides a formula for calculating the critical speed for tipping, relating it to the dimensions of the box and the radius of curvature.
  • Another participant expresses appreciation for the insights shared and confirms their approach to the problem.
  • One participant asserts that if the bottom board(s) were on the pallet, tipping would not occur, introducing a different perspective on the problem.

Areas of Agreement / Disagreement

Participants express varying views on the dynamics of tipping, with some agreeing on the conditions for tipping while others introduce alternative considerations. The discussion remains unresolved regarding the exact calculations and conditions for tipping.

Contextual Notes

Participants mention various assumptions and conditions, such as the neglect of the forklift's dynamics and the rigid body nature of the box and pallet. There is also an emphasis on the role of the center of gravity and the timing of actions taken by the forklift operator.

Who May Find This Useful

This discussion may be of interest to those studying dynamics, mechanical engineering, or anyone involved in practical applications of physics related to load stability and motion in vehicles.

co0ldood
Messages
8
Reaction score
0
Hello all. I have a problem and I’m not sure if my analysis is 100% accurate. I hope this is the correct spot since it deals with dynamics (mechanics).

Here’s my scenario:
I have a forklift and a pallet with a box on top. I’m trying to calculate the required velocity for the box+pallet to flip around a turn.. and at what angle. Pictures have been uploaded to visualize the problem better.

http://img.photobucket.com/albums/v114/Co0lDood/prob.jpg

Here are my following assumptions:
- Forklift is 100% capable of carrying this load (forklift will NOT tilt on the turn and I can neglect the forklift all together)
- Box is latched down to pallet creating a rigid body.
- Center of gravity (CoG) is directly in the middle of the box.
- The fork lift is at constant velocity (acceleration = 0), which makes centripetal force only acting in the normal direction into the curve.
- No slipping will occur between the fork and the pallet + box.

Known
- I can calculate the velocity, radius of curvature, and all dimensions of the box/pallet.

Centripetal force is Fc= (v^2)/r (in the normal direction toward the curve)
Centrifugal force is the same in magnitude but is acting on the opposite direction at the CoG.

I calculated the angle of when my rigid system will fall over by having the CoG align vertically to point P (as seen in picture) in a static situation.

How would I go about calculating how much force is required to have my rigid body reach the angle I calculated? (so my pallet + box will flip)

I have thought about calculating the moment at point P and CoG (Sum of moment at a point in the free body diagram and equaling it to the sum of moments, at the same point, in the mass-acceleration diagram or kinetic diagram), but I can’t seem to relate it with everything else.

I'm not sure how to go about calculating angular acceleration either.

Can't seem to put everything together. I don’t think I have left anything out.

Any theories or comments would be greatly appreciated. Thank you for your time!
 
Physics news on Phys.org
Maybe this should me moved to the "homework style" question? Could the mods move this thread if you think it is suitable over there. Thank you.
 
I am not sure what your unknowns are. The block will start to tip once the torque from the centripetal 'pseudo' force (the inertial force, mv^2/r, applied at the cg, which is the friction force at the base which provides the centripetal force necessary for curved motion), about the lower right corner, overcomes the torque from the gravity force about that corner. If you know the box dimensions, M., and r, then solve for v. Once the box starts to tip, and the same speed v is maintained, its ultimate tip over is inevitable. It doen't have to wait for the cg to be over the tipping corner. I don't generally like using pseudo forces, but it has its place here; be sure to label your FBD as 'FBD with Pseudo Forces'. If this is a homework question, it should be moved by the moderators for further help. Is it?
 
It is not a homework question, more of a conceptual problem for work. What is given is the weight and the dimension of the box

Lets say the box starts to tip, but prior to ultimate tip over, the forklift would slow down or straighten out which will lower 'pseudo' force. Ideally, will the box come back down if I were to sum the moments “or torque” at the corner with the tip angle? (assuming the weight moment overcame the moment of the centripetal ‘pseudo’ force)


I really appreciate the help!
 
Oh, yes. If the box c.g. is say a horizontal distance 'd' from the corner, and a vertical distance 'h' up from the base, the critical speed for the start of tipping can be calculated from (mv^2/r)(h) = mg(d). Now at just beyond this point, the box starts to rotate and accelerate (angularly) under the net torque , but if you reduce the forklift speed well before the cg is over the corner of tipping, it will bounce back, since the net torque will be in the the other direction, but you've got to act fast, because the box must first come to an angular stop before reversing its rotation, and if the cg goes past the corner, it's too late!
 
PhanthomJay said:
Oh, yes. If the box c.g. is say a horizontal distance 'd' from the corner, and a vertical distance 'h' up from the base, the critical speed for the start of tipping can be calculated from (mv^2/r)(h) = mg(d). Now at just beyond this point, the box starts to rotate and accelerate (angularly) under the net torque , but if you reduce the forklift speed well before the cg is over the corner of tipping, it will bounce back, since the net torque will be in the the other direction, but you've got to act fast, because the box must first come to an angular stop before reversing its rotation, and if the cg goes past the corner, it's too late!

Thank you PhanthomJay. That was how I was going about the problem.. just double checking! I really appreciate the help.

This forum seems great, maybe I'll stick around and try to spread some of my knowledge to others!
 
If the bottom board(s) were on the pallet it would not tip over!
 

Similar threads

Undergrad Axial angular momentum calculation
  • · Replies 30 ·
2
Replies
30
Views
5K
Undergrad How find moment of inertia for car in turn?
  • · Replies 49 ·
2
Replies
49
Views
6K
Undergrad Moment of Inertia about an axis and Torque about a point
  • · Replies 5 ·
Replies
5
Views
3K
Undergrad Resolve moment of inertia at an angle
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Moment of inertia of human body with limbs at an angle
  • · Replies 12 ·
Replies
12
Views
2K
Undergrad Properties of angular momentum
  • · Replies 6 ·
Replies
6
Views
1K
Undergrad Moment of inertia where mass and torque are at a different positions
  • · Replies 69 ·
3
Replies
69
Views
6K
Graduate How can I calculate the moment of inertia of any object?
  • · Replies 10 ·
Replies
10
Views
3K
Graduate Torque and Moment of Inertia of a Lever Arm
  • · Replies 2 ·
Replies
2
Views
4K
Undergrad How Does Centrifugal Force Affect Objects on a Rotating Disk?
  • · Replies 18 ·
Replies
18
Views
3K