Why is the driven gear's torque's direction clockwise?

  • #1
annamal
387
33
TL;DR Summary
Two gears (A and B) are spinning with their centers fixed with the left one being the driver driving the left gear clockwise. Why is the driven gear (gear B to the right) torque clockwise as well?
We have two gears A and B (left and right). Gear A is driven with a clockwise torque. Why is gear B's torque also clockwise? I would say that if gear B is driven to turn counterclockwise, the torque should be in the counterclockwise direction.
Screenshot 2023-09-12 at 7.09.39 PM.png
 
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  • #2
If the left gear is turning clockwise, the right gear will turn counterclockwise. Is the torque you are applying to A against the rotation or something?
 
  • #3
berkeman said:
If the left gear is turning clockwise, the right gear will turn counterclockwise. Is the torque you are applying to A against the rotation or something?
No. I am applying a torque just to gear A. And apparently the torque for gear B is in the opposite direction because it is some reaction torque to gear A.
 
  • #4
I assume what's being described is the force applied by gear B to gear A. If gear A applies a force downwards at the point of contact, gear B must be applying a force back against it upwards per Newton's 3rd law.
 
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  • #5
annamal said:
No. I am applying a torque just to gear A. And apparently the torque for gear B is in the opposite direction because it is some reaction torque to gear A.
Sure, just use the Right-Hand Rule for torques to help you see what is going on. Draw the force and torque vectors for each gear...
$$\vec \tau = \vec R \times \vec F$$
 
  • #6
Ah. I figured it out. The torque for the right gear is drawn as the load's torque.
 
  • #7
annamal said:
Ah. I figured it out. The torque for the right gear is drawn as the load's torque.
Correct.
Consider that the magnitude of each torque depends on the diameter (or number of teeth) of each gear.
Only the tangential contact forces mentioned in post #4 are of equal magnitude and opposite directions.

Force (or torque) and resistance to it are always a pair.
We can't talk about a driving torque, unless we have a resisting torque.
In the same way, we can't exert any weight on the floor of a free-falling elevator.

FREE-BODY-DIAGRAM-OF-TWO-GEAR.png
 

FAQ: Why is the driven gear's torque's direction clockwise?

Why does the driven gear's torque direction depend on the driving gear?

The direction of the driven gear's torque depends on the direction of rotation of the driving gear. When two gears mesh, the teeth of one gear push against the teeth of the other, causing it to rotate in the opposite direction. If the driving gear rotates clockwise, the driven gear will rotate counterclockwise, and vice versa.

What factors influence the direction of torque in a gear system?

The direction of torque in a gear system is influenced by the arrangement of the gears (whether they are spur, helical, bevel, etc.), the direction of rotation of the driving gear, and the way the gears are meshed. The physical interaction between the gear teeth determines the torque direction.

Can the driven gear's torque direction be controlled or changed?

Yes, the driven gear's torque direction can be controlled or changed by altering the configuration of the gear system. For instance, introducing an idler gear between the driving and driven gears can reverse the direction of the driven gear's torque. Additionally, changing the orientation or type of gears can also affect the torque direction.

Why is understanding the torque direction important in mechanical systems?

Understanding the torque direction is crucial for designing and operating mechanical systems efficiently. It ensures that the components move as intended, prevents mechanical failure, and optimizes the performance of the system. Incorrect torque direction can lead to undesired motion, increased wear, and potential damage to the system.

How does gear ratio affect the torque direction in a gear system?

The gear ratio affects the magnitude of the torque but not the direction. The gear ratio is the ratio of the number of teeth on the driven gear to the number of teeth on the driving gear. While it influences the speed and torque magnitude, the direction of torque is determined by the interaction between the gear teeth and the direction of rotation of the driving gear.

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