- #1
Taulant Sholla
- 96
- 5
Homework Statement
Homework Equations
work-kinetic energy theorem
Work done by torque: wheel turning about a curb
Click For Summary
SUMMARY
The discussion centers on calculating the work done by torque when a wheel turns about a curb, specifically addressing the application of the work-kinetic energy theorem. Participants emphasize the necessity of understanding that the net work (Wnet) cannot equal zero if a constant force is applied, and they suggest using virtual work for statics problems. The conversation highlights the importance of accurately determining the force required to initiate the wheel's rise and the rotational kinetic energy once it clears the curb. Key errors discussed include miscalculating average force and misunderstanding the relationship between displacement and angular displacement.
PREREQUISITES- Understanding of the work-kinetic energy theorem
- Familiarity with torque and its equilibrium conditions
- Knowledge of virtual work principles in statics
- Basic concepts of rotational kinetic energy
- Study the application of the work-kinetic energy theorem in rotational dynamics
- Explore virtual work methods for solving statics problems
- Learn about torque equilibrium and its implications for force calculations
- Investigate the relationship between linear displacement and angular displacement in rotational systems
Physics students, mechanical engineers, and anyone studying dynamics and statics in relation to rotational motion and torque calculations.
work-kinetic energy theorem
- #2
TSny
Science Advisor
Homework Helper
Gold Member
- 14,804
- 4,802
You've assumed that it is possible for Wnet to equal zero when F is constant. Try to see why this can't be true.
Can you figure out how much force is required to get the wheel to start to rise?
Can you figure out how much force is required to get the wheel to start to rise?
- #3
- 42,804
- 10,495
Further to TSny's hints...
You write that you have to solve it by the Work-KE theorem. I suspect you have misunderstood the requirement. As TSny writes, you have no guarantee that ##\Delta KE=0##.
You can solve statics problems using virtual work. Maybe that is what you are supposed to be using? But that method considers infinitesimal changes in position, not integrating over a substantial change.
You write that you have to solve it by the Work-KE theorem. I suspect you have misunderstood the requirement. As TSny writes, you have no guarantee that ##\Delta KE=0##.
You can solve statics problems using virtual work. Maybe that is what you are supposed to be using? But that method considers infinitesimal changes in position, not integrating over a substantial change.
- #4
Taulant Sholla
- 96
- 5
Ah, yes. Thank you. It would take a variable force to result in a final kinetic energy of 0. I know torque equilibrium yields the constant force required to offset the torque produced by gravity. Thank you again.TSny said:
- #5
Taulant Sholla
- 96
- 5
Right. Thank you. I need to find the rotational kinetic energy of the wheel once it rises to the top of the curb.haruspex said:
- #6
Hamal_Arietis
- 156
- 15
You assumed that ##ds=Rd\theta## but ##ds>0## and ##d\theta <0##. So it is wrong
If you assumed that ##ds=-Rd\theta## I think you will get answer
If you assumed that ##ds=-Rd\theta## I think you will get answer
- #7
Monsterboy
- 305
- 96
Isn't that angle = 30o ?
- #8
- 42,804
- 10,495
Taulant's error was to calculate a funny kind of average force (averaged over horizontal distance, which is not what is meant by "average force") necessary to provide the PE gain. Instead, the force to be found is the minimum constant force that will get it over the step. The next stage is to find the residual KE that results. That could be done by integration, but it is not necessary.Hamal_Arietis said:
Taulant set θ as the angle to the vertical, the 60o. That reduces as the wheel rises.Monsterboy said: