Is engine torque a static force?

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Discussion Overview

The discussion centers around the nature of engine torque, specifically whether it can be considered a static force. Participants explore the relationship between torque, work, and power in the context of an engine producing torque at a certain RPM, examining both static and dynamic scenarios.

Discussion Character

  • Conceptual clarification
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant questions if 100 Nm of torque at 3000 RPM is a static force, suggesting that torque does not move anything until it does work, which relates to power.
  • Another participant clarifies that while the engine produces 100 Nm of torque, the reaction torque is doing zero work since the engine is stationary.
  • A subsequent reply reinforces the idea that torque can be static when not overcoming friction, and dynamic when in motion.
  • Some participants argue that dynamic torque equates to work, while others challenge this by stating that torque is simply torque, and work is defined through torque and angular displacement.
  • There is a discussion about the relationship between torque and forces, emphasizing that if torque or force is not moving, it is not doing work.
  • One participant highlights the action-reaction principle, explaining that while the engine exerts torque on the driveshaft, the fixed engine block does not perform work on the chassis.
  • Another participant expresses confusion and requests further clarification on the relationship between reaction forces and work.
  • One participant critiques the tendency to ascribe meanings to terms without proper understanding, suggesting that clarity in definitions is crucial.

Areas of Agreement / Disagreement

Participants do not reach a consensus on whether torque can be classified as a static force. There are competing views on the definitions and implications of static versus dynamic torque, as well as the relationship between torque and work.

Contextual Notes

Some statements rely on specific definitions of torque and work, which may vary among participants. The discussion includes unresolved mathematical relationships and assumptions about the conditions under which torque is considered static or dynamic.

vysqn
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Maybe stupid question but it confuses me:)
For Example engine produces 100Nm of torque at 3000RPM. So that's mean that this 100Nm at 3000RPM in this particular moment is static force? Because torque doesn't move anything. If it start to spin, it doing work and work over time is POWER. (~43Hp at this example)
Is this correct?

Thank's !
 
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If the engine is producing 100 Nm of torque to a shaft spinning 3000 RPM, then the shaft is delivering 42 hp of work to whatever is connected to the shaft.

But the engine, which is stationary, has an equal 100 Nm of reaction torque. The reaction torque is doing zero work because the engine is not moving.

If the shaft is not connected to a load, just spinning free, then the engine is producing zero torque and zero power. The engine may be capable of producing 100 Nm of torque, but it is only producing that torque if it is connected to an appropriate load.
 
"The reaction torque is doing zero work because the engine is not moving."
So that's mean torque is static force. Back to the example, at 3000rpm it produces 100Nm on this particular snapshot in time
 
vysqn said:
So that's mean torque is static force

You're trying to over-define.

Torque is torque.
Torque can be static as when you're pulling on a wrench and the bolt has not yet begun to turn because you have not yet overcome friction.
Torque can be dynamic (ie in motion) after the bolt has begun to turn and is now moving against friction.
 
So, dynamic torque = work
 
If it helps...The equations for linear an rotational motion are similar...

Work = force * displacement
Work = torque * angular displacement

Power = Work/time
So..
Power = force * velocity
Power = torque * angular velocitySo torques work like forces. If the torque (or force) isn't moving it's not doing any work. If it is moving then it is doing work.
 
Last edited:
In your example the shaft is rotating so it's doing work. The reaction force trying to move the engine in its mounting blocks is not moving so it's not doing work.
 
CWatters said:
The reaction force trying to move the engine in its mounting blocks is not moving so it's not doing work.
Don't understand - can You put more information here
 
"For every action there is an equal and opposite reaction".

When the engine turns the drive shaft clockwise there is an equal but opposite reaction torque that tries to turn the engine block anti-clockwise. However the engine block is fixed to the car so it cannot rotate. The engine does work on the driveshaft. The engine block does not do work on the chassis.
 
  • #10
vysqn said:
So, dynamic torque = work
no.

you're trying to ascribe meaning instead of looking it up.

Torque is torque. Work is torque X displacement by rotation, as stated more eloquently by @CWatters in post 6.
CWatters said:
Work = torque * angular displacement

The mind will concatenate words because they sound good even if the concept conveyed is dead wrong. That's how you get "Word Salad" ..

slide 12 here https://slideplayer.com/slide/4773534/
Work+done+by+a+torque+Torque+%3D+force+times+lever+arm+t+%3D+Fr.jpg
 

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  • #11
Thank You Guys!

I will analyze those informations for better understanding this principals.
 

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