How is torque calculated on a shaft with a force applied at the end?

[helpinghand]

Just a really basic question, say you have a shaft about 25meters long and at the end of the shaft there is a force of 3412KN, what is the torque of the shaft?

T = F*d

does that mean that T = 3412*25 = 85300KNm

is that right?

 

[tiny-tim]

hi helpinghand!

if the force is perpendicular to the shaft, then yes

 

[DickL]

Just remember that the 'd' in the equation is distance (lever arm length) not diameter. Unless the force is a couple the d (distance) is equal to half the diameter of the shaft. You've referred to a shaft, which to me means it rotates about its longitudinal axis.
Or is it a 25 m long lever.

 

[SteamKing]

You really haven't described how the shaft is supported and how the load is applied.
For example, a shaft 25 m long probably has some supports/bearings along its length.
What kind of shaft? Is it used for power transmission? Is it circular (and what is its diameter?) With regard to the load, is it applied in such a manner that it will bend the shaft or twist it? If the load will twist the shaft, then that is usually referred to as a torque. If the load is applied such that it will cause the shaft to deflect from its original centerline, this is usually referred to as a bending moment.

 

[helpinghand]

You really haven't described how the shaft is supported and how the load is applied.
For example, a shaft 25 m long probably has some supports/bearings along its length.
What kind of shaft? Is it used for power transmission? Is it circular (and what is its diameter?) With regard to the load, is it applied in such a manner that it will bend the shaft or twist it? If the load will twist the shaft, then that is usually referred to as a torque. If the load is applied such that it will cause the shaft to deflect from its original centerline, this is usually referred to as a bending moment.

Here is the image of how it looks and this is a shaft. So there will be torque applied on the length of the shaft.

So eventhough it has a support in the centre, does T = 25*3412 ?

Thanks

 

[SteamKing]

You have a bending moment created at the fixed end of the shaft by the vertical load applied at the free end. A torque is usually taken to mean a moment which twists the shaft about an axis running along the length of the shaft.

 

[tiny-tim]

hi helpinghand!

Here is the image of how it looks and this is a shaft. So there will be torque applied on the length of the shaft.

ah, that's what i thought

So eventhough it has a support in the centre, does T = 25*3412 ?

yes, the torque about a particular point is the same no matter what other forces are present

of course, when you calculate the actual strain or acceleration or whatever, you'll have to add the torque of the reaction force at the centre support

A torque is usually taken to mean a moment which twists the shaft about an axis running along the length of the shaft.

if you mean for a shaft only, then yes in physics or engineering "shaft" usually means something which can only rotate about its own longitudinal axis

however, as a matter of english, this is a minority meaning, and "shaft" generally means much the same as "beam" …

noun
1 a long, narrow part or section forming the handle of a tool or club, the body of a spear or arrow, or a similar implement : the shaft of a golf club | the shaft of a feather.
• an arrow or spear.
• a column, esp. the main part between the base and capital.
• a long cylindrical rotating rod for the transmission of motive power in a machine.
• each of the pair of poles between which a horse is harnessed to a vehicle.
• a ray of light or bolt of lightning : a shaft of sunlight.
• a sudden flash of a quality or feeling : a shaft of inspiration.
• a remark intended to be witty, wounding, or provoking : he directs his shafts against them.​