Torque vs Energy. Same units, not the same thing

[SameSame]

Hahaha that's pretty good. But the units check out. Not intuitive but yet still true.

[SameSame]

A quick Google will show you

[dans79]

Hahaha that's pretty good. But the units check out. Not intuitive but yet still true.

OK show us the unit derivations then, that proves you right and all of us wrong!

[dans79]

A quick Google will show you

lol, you expect the internet to be right when it comes to physics.

[Cold Fussion]

Hahaha that's pretty good. But the units check out. Not intuitive but yet still true.

But it just doesn't check out at all. If torque is energy, how would one apply the conservation of energy in a gearbox? I have a torque at the input shaft and a different torque at the output shaft, if torque is energy, then where did this extra come from? Perhaps the teapot floating around Venus put it there? Similarly, if radians are a dimensionless unit, then why don't we measure angular velocity in hertz? You contend that radians are a dimensionless unit but that isn't really correct. The International Bureau of Weights and Measures states:

In practice, with certain quantities, preference is given to the use of certain special unit names, or combinations of unit names, to facilitate the distinction between different quantities having the same dimension. When using this freedom, one may recall the process by which the quantity is defined. For example, the quantity torque may be thought of as the cross product of force and distance, suggesting the unit newton metre, or it may be thought of as energy per angle, suggesting the unit joule per radian. The SI unit of frequency is given as the hertz, implying the unit cycles per second; the SI unit of angular velocity is given as the radian per second; and the SI unit of activity is designated the becquerel, implying the unit counts per second. Although it would be formally correct to write all three of these units as the reciprocal second, the use of the different names emphasises the different nature of the quantities concerned. Using the unit radian per second for angular velocity, and hertz for frequency, also emphasizes that the numerical value of the angular velocity in radian per second is 2pi times the numerical value of the corresponding frequency in hertz.

This post was shameless plagurised from amc's post in 2012.

[SameSame]

Hahaha that's pretty good. But the units check out. Not intuitive but yet still true.

OK show us the unit derivations then, that proves you right and all of us wrong!

I just showed you. Look at the previous page of how power is derived. 1 N.m = 1 J. Fact.

But I'll go again. Power has units of J/s. Torque (N.m) x Angular velocity (radians/s) = radians.N.m/s. A radian is DIMENSIONLESS. Therefore, N.m/s = J/s

[SameSame]

Hahaha that's pretty good. But the units check out. Not intuitive but yet still true.

But it just doesn't check out at all. If torque is energy, how would one apply the conservation of energy in a gearbox? I have a torque at the input shaft and a different torque at the output shaft, if torque is energy, then where did this extra come from? Perhaps the teapot floating around Venus put it there? Similarly, if radians are a dimensionless unit, then why don't we measure angular velocity in hertz? You contend that radians are a dimensionless unit but that isn't really correct. The International Bureau of Weights and Measures states:

In practice, with certain quantities, preference is given to the use of certain special unit names, or combinations of unit names, to facilitate the distinction between different quantities having the same dimension. When using this freedom, one may recall the process by which the quantity is defined. For example, the quantity torque may be thought of as the cross product of force and distance, suggesting the unit newton metre, or it may be thought of as energy per angle, suggesting the unit joule per radian. The SI unit of frequency is given as the hertz, implying the unit cycles per second; the SI unit of angular velocity is given as the radian per second; and the SI unit of activity is designated the becquerel, implying the unit counts per second. Although it would be formally correct to write all three of these units as the reciprocal second, the use of the different names emphasises the different nature of the quantities concerned. Using the unit radian per second for angular velocity, and hertz for frequency, also emphasizes that the numerical value of the angular velocity in radian per second is 2pi times the numerical value of the corresponding frequency in hertz.

Let's take a gearbox for example. Power is conserved between gears and that is exactly how a gearbox works. The bigger gear has more torque but a lower speed where as the small gear has less torque but a higher speed. The different speeds and torques can be computed if the gear ratio is know. I.e A gear ratio of 2:1 means the bigger gear has twice the torque and half the speed of the smaller one.

Energy is conserved because if you multiply the power by some time then both have the same amount of energy.

You answered your post about Hz and rad/s in your own quote. It is done to distinguish the two from each other. Exactly the same reason why Nm and J are used in each other their respective "cases"

[Jolle]

Hahaha that's pretty good. But the units check out. Not intuitive but yet still true.

OK show us the unit derivations then, that proves you right and all of us wrong!

I just showed you. Look at the previous page of how power is derived. 1 N.m = 1 J. Fact.

But I'll go again. Power has units of J/s. Torque (N.m) x Angular velocity (radians/s) = radians.N.m/s. A radian is DIMENSIONLESS. Therefore, N.m/s = J/s

Isn't torque the amount if force (in N) at a meter and not over a meter (if in a second makes it a watt)?

[dans79]

Hahaha that's pretty good. But the units check out. Not intuitive but yet still true.

OK show us the unit derivations then, that proves you right and all of us wrong!

I just showed you. Look at the previous page of how power is derived. 1 N.m = 1 J. Fact.

But I'll go again. Power has units of J/s. Torque (N.m) x Angular velocity (radians/s) = radians.N.m/s. A radian is DIMENSIONLESS. Therefore, N.m/s = J/s

sorry it doesn't work that way. If you are balancing unit equations, you have to use base units.

• length
• mass
• time

[Cold Fussion]

That's the point, if torque is energy than the torque at the output shaft must be the same as the torque at the input shaft.

[SameSame]

You are looking at it incorrectly. Power is conserved and not torque. The measurement units at the input are J/s and at the output they are J/s, these two quantities are the same.

Without any MOTION no torque would be transferred. Therefore energy is conserved.

[SameSame]

OK show us the unit derivations then, that proves you right and all of us wrong!

I just showed you. Look at the previous page of how power is derived. 1 N.m = 1 J. Fact.

But I'll go again. Power has units of J/s. Torque (N.m) x Angular velocity (radians/s) = radians.N.m/s. A radian is DIMENSIONLESS. Therefore, N.m/s = J/s

sorry it doesn't work that way. If you are balancing unit equations, you have to use base units.

• length
• mass
• time

Please define a joule for me in terms of SI units and you will see I am correct. I should have done that in the first place.

[FoxHound]

I'm reading that horsepower is a (nigh on)fictitious measurement designed to give an apt description to prospective buyers as to the indication of the power.

James Watt responsible.

Torque is measurable, and a complete indicator of the rotational force.

So why would it not be plausible that a 150bhp 200nm Diesel of same mass and size to that of a 170bhp 120nm Petrol, would be quicker.
It has more rotational force, and the as Horspeower is defined from inception as thus:

To get industries to begin adopting his steam engines, Watt came up with the term horsepower so buyers could have a way of comparing his engines with more traditional power sources. One version of how Watt first calculated the meaning of horsepower starts with an early customer, a saw mill that replaced horses with a steam engine. The horses were attached to a 24-foot diameter wheel, which yields to a circumference of 75.4 feet around. Watt determined each horse's pulling force and came up with an average of 180 pounds per animal. He counted that the horses turned the wheel 144 times per hour, which is 2.4 times per minute. With a 75.4-foot path around the wheel, each horse was moving 181 feet per minute. Multiply the feet per minute (181) by the force of each horse (180) and you arrive at 32,580. Watt did the same and rounded up to an even 33,000-lbs.ft. per minute to determine the value of one, single horsepower.

http://www.hemmings.com/magazine/hmn/20 ... 18941.html
It suggests that Horsepower was designed to give indication of the power available over a timed period, in the above a minute being the timed period.

So to my mind, and without the math, it suggest exactly what the Yuasa engineer was purporting over a cold one.
The petrol can deliver it's torque quicker, but it's torque, or rotational force, is circa 40% down on the Diesel, which in turn is circa 15% down in terms of horspower.

[Jolle]

I just showed you. Look at the previous page of how power is derived. 1 N.m = 1 J. Fact.

But I'll go again. Power has units of J/s. Torque (N.m) x Angular velocity (radians/s) = radians.N.m/s. A radian is DIMENSIONLESS. Therefore, N.m/s = J/s

sorry it doesn't work that way. If you are balancing unit equations, you have to use base units.

• length
• mass
• time

Please define a joule for me in terms of SI units and you will see I am correct. I should have done that in the first place.

You're missing distance.

Torque changes trough gearing, but not the power (because of time and distance).

The m in torque amount of force at a meter from the rotation and is not distance traveled like in energy (a lift of one newton over a meter in a second)

Torque has no movement or time.

On the crackshaft, with a bit if a lever, you can stop an engine with your bare hands (only around 50kg on a meter wide wheel) but put trough a gearbox, reduced in speed at the rear wheels, it'll rip your arms off.

[SameSame]

I'm sorry I'm busy using my phone but I'll show you later a proper derivation using a computer.

Please do some reading on how a gearbox works. Just google is power conserved between gears and you will see thousands of links confirming that.

Energy has no units of seconds in it.

I'll say it one last time. Power is constant through gears and torque is what changes. Without any spinning motion of the gears no torque is transmitted and therefore the conservation of energy is not violated. As soon as the gears move POWER is transferred between gears and therefore ENERGY IS CONSERVED as you just have to multiply the power by time to get the energy.