Torque and Rotational Kinetic Energy Relationship

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Discussion Overview

The discussion revolves around the possibility of calculating Kinetic Energy or Rotational Kinetic Energy of an object using Power (kW), Torque (Nm), and Speed (RPM). The scope includes theoretical considerations and practical implications of these relationships in physics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question whether it is possible to calculate Kinetic Energy or Rotational Kinetic Energy with the given parameters, suggesting that additional information may be necessary.
  • One participant emphasizes that power refers to energy transfer and cannot be attributed to an object without a receiving entity, prompting a request for clarification on the scenario.
  • Another participant notes that power can be derived from torque and speed, indicating redundancy in the parameters provided.
  • It is mentioned that calculating kinetic energy requires knowledge of speed and the moment of inertia of the object.
  • A participant explains that while power indicates the rate of energy flow, it does not reveal the total energy or angular momentum contained within the object, highlighting the differences in kinetic energy and angular momentum between objects with the same power and torque.
  • There is a detailed explanation of how to calculate power from torque and rotation rate, including a conversion from RPM to radians per second.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of calculating Kinetic Energy or Rotational Kinetic Energy with the given parameters. There is no consensus on the necessity of additional information or the implications of power in relation to energy content.

Contextual Notes

Some limitations include the need for clarity on the scenario involving the object, as well as the dependence on definitions such as power and energy transfer. The discussion also reflects uncertainty regarding the relationship between the parameters and the calculations involved.

alichoudhry57
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I am wondering if it is possible to calculate either the Kinetic Energy or Rotational Kinetic Energy of an object if we have the Power (kW), Torque (Nm), and Speed (RPM) of the object.
 
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alichoudhry57 said:
I am wondering if it is possible to calculate either the Kinetic Energy or Rotational Kinetic Energy of an object if we have the Power (kW), Torque (Nm), and Speed (RPM) of the object.
Depends, but probably not. Do we have a continuous function for those? Is there any more info you can provide on your scenario?
 
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alichoudhry57 said:
I am wondering if it is possible to calculate either the Kinetic Energy or Rotational Kinetic Energy of an object if we have the Power (kW), Torque (Nm), and Speed (RPM) of the object.
Welcome @alichoudhry57 !
Objects can’t have those by themselves, as power refers to a transfer of energy, you need at least another object or substance receiving that energy.
Therefore, could you please clarify your reference to that object?
 
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alichoudhry57 said:
Power (kW), Torque (Nm), and Speed (RPM) of the object.
Power can be computed from torque and speed, so it is redundant.

Finding the kinetic energy requires knowing the speed, and the moment of inertia of the object.
https://en.wikipedia.org/wiki/Moment_of_inertia
 
alichoudhry57 said:
I am wondering if it is possible to calculate either the Kinetic Energy or Rotational Kinetic Energy of an object if we have the Power (kW), Torque (Nm), and Speed (RPM) of the object.
Power tells you the rate at which energy is flowing through the object. It will not tell you how much energy or angular momentum the object contains. A drive shaft with an attached flywheel and a second drive shaft without can have the same power and torque passing through and can be rotating at the same rate. But the amount of kinetic energy and angular momentum that the two contain can be dramatically different.

If you have torque in Nm and rotation rate in RPM then you can get power in kilowatts. Indeed, given any two of the three, you can calculate the one you do not know.

For power, first convert RPM to radians per second (multiply by 0.104719755). Multiply torque in Nm by rotation rate in rad/s to get power in watts. Then divide by 1000 to get power in kilowatts.

Edit: scooped by @Baluncore on the power from torque and speed calculation.
 

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