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Re: Torque vs Energy. Same units, not the same thing
Posted: 11 Aug 2016, 08:24
by SameSame
Jolle wrote:SameSame wrote:Centripetal forces have everything to do with inertia… A massless object would experience no cevtripitel force
Or my sense of humor has taken a nose dive after a long day
Again you're almost right but also wrong. A spinning mass has an inertia energy stored inside it's mass and movement. A spinning object also experience rotational force.
A roling car for instance does have inertia but not a rotational force or what kind of force whatsoever.
The centrifugal force is a result of a constant but fixed at 90% of the centreline, change of direction of the mass
In what way am I wrong?
Not sure what you mean by fixed at 90% of centerline, change of direction of the mass.
An object with an angular velocity will experience centripetal forces. For example jet engine blades are made from high strength super alloys because of this. They have to with stand massive centripetal forces. So to say something that is spinning experiences no forces is incorrect.
Re: Torque vs Energy. Same units, not the same thing
Posted: 11 Aug 2016, 08:28
by SameSame
Cold Fussion wrote:Furthermore if torque is energy, then power would be time derivative of torque, which is absolutely not the same as power = torque * angular velocity.
Well power is Torque multiplied by the time derivative of the angle ( which is angular velocity)
For example you could integrate the power with respect to time and the torque with respect to the angle and solve for example the angle the torque went through over a certain time period at a certain power.
Re: Torque vs Energy. Same units, not the same thing
Posted: 11 Aug 2016, 08:57
by Jolle
SameSame wrote:Jolle wrote:SameSame wrote:Centripetal forces have everything to do with inertia… A massless object would experience no cevtripitel force
Or my sense of humor has taken a nose dive after a long day
Again you're almost right but also wrong. A spinning mass has an inertia energy stored inside it's mass and movement. A spinning object also experience rotational force.
A roling car for instance does have inertia but not a rotational force or what kind of force whatsoever.
The centrifugal force is a result of a constant but fixed at 90% of the centreline, change of direction of the mass
In what way am I wrong?
Not sure what you mean by fixed at 90% of centerline, change of direction of the mass.
An object with an angular velocity will experience centripetal forces. For example jet engine blades are made from high strength super alloys because of this. They have to with stand massive centripetal forces. So to say something that is spinning experiences no forces is incorrect.
There are forces at work yes, but it's got noting to to with inertia.
Re: Torque vs Energy. Same units, not the same thing
Posted: 11 Aug 2016, 09:28
by J.A.W.
Are you sure?
Potential energy, like electricity held captive in a battery.. it is still energy, but not yet active in the 4th dimension..
..or as torque held captive in a stalled electro-motor shaft is still energy, just as per a cocked crossbow or torsion spring..
Re: Torque vs Energy. Same units, not the same thing
Posted: 11 Aug 2016, 09:32
by Shooty81
Jolle wrote:SameSame wrote:Jolle wrote:
Again you're almost right but also wrong. A spinning mass has an inertia energy stored inside it's mass and movement. A spinning object also experience rotational force.
A roling car for instance does have inertia but not a rotational force or what kind of force whatsoever.
The centrifugal force is a result of a constant but fixed at 90% of the centreline, change of direction of the mass
In what way am I wrong?
Not sure what you mean by fixed at 90% of centerline, change of direction of the mass.
An object with an angular velocity will experience centripetal forces. For example jet engine blades are made from high strength super alloys because of this. They have to with stand massive centripetal forces. So to say something that is spinning experiences no forces is incorrect.
There are forces at work yes, but it's got noting to to with inertia.
In a physical sense, mass is inertia.
If you consider a mass element at constant speed going around a circle, the inertia is the cause for the centripetal force to appear. Without the centripetal force it would just go straight. Without the mass ther would be no centripetal force. They are directly related. If you have a object roatating around its center of mass, there won't be external forces, however every single mass element of the object has its own inertia, just that the centripetal forces cancel each other out.
Re: Torque vs Energy. Same units, not the same thing
Posted: 11 Aug 2016, 21:03
by godlameroso
Again, this long winded discussion is why it's just easier to measure torque at some other reference point, like directly at the end of the crank/flywheel or the wheels. Because the conversion of chemical to mechanical energy is a very inefficient process with thousands of confounding variables. It's easier to just assume an average of all the combustion events, masses and inertia as one output, and call it torque. It's a simplification which ignores a sea of interdependent variables such as friction, leverage, balance forces, harmonics, vibration, temperature, temperature gradients, imperfections in the machined surfaces.
Re: Torque vs Energy. Same units, not the same thing
Posted: 11 Aug 2016, 23:48
by PlatinumZealot
Torque can be stored as energy. You torque a spanner and hold it in place. You compress a spring and hold it in place. That is torque being stored as energy (stationary torque).
Re: Torque vs Energy. Same units, not the same thing
Posted: 12 Aug 2016, 00:55
by SameSame
PlatinumZealot wrote:Torque can be stored as energy. You torque a spanner and hold it in place. You compress a spring and hold it in place. That is torque being stored as energy (stationary torque).
If we assume the torque is applied the end of a rod, then U = T^2*L/(2*J*G) where;
U = Strain energy in the entire length of the rod
T = Torque applied
L = Length of the rod
J = Second moment of area ie pi/2*r^4 in this case
G = Shear modulus of material
Obviously this only applies to the linear elastic region and this is assuming a constant torque is applied.
Edit: A powerful way to measure deflections at certain points in an object is to use the conservation of energy. A large force acting on an object will give it energy (the object will deform ie the force will displace a certain point), and by conserving this energy the deflections/internal forces at other points can be calculated.
Re: Torque vs Energy. Same units, not the same thing
Posted: 12 Aug 2016, 02:09
by J.A.W.
An ancient example of practical utility, viz :
http://www.abong.com/images/ballista.png
Re: Torque vs Energy. Same units, not the same thing
Posted: 12 Aug 2016, 23:04
by rjsa
That's stretching hemp fibers. In the end, with any kind of spring, it's hooke's law and it can be modelled as compressing/stretching within the material.
Re: Torque vs Energy. Same units, not the same thing
Posted: 13 Aug 2016, 03:12
by J.A.W.
Some ballistas used animal tendons as the 'spring' energy medium.
See here:
https://www.youtube.com/watch?v=pUsJHntAJL0 for the energy/torque release by muscles, in a cat jumping.
Re: Torque vs Energy. Same units, not the same thing
Posted: 13 Aug 2016, 15:11
by rjsa
Note that the SI units of torque is a Newton-metre, which is also a way of expressing a Joule (the unit for energy). However, torque is not energy. So, to avoid confusion, we will use the units N.m, and not J. The distinction arises because energy is a scalar quanitity, whereas torque is a vector.
Re: 2016 Mercedes AMG Petronas F1 Team - Mercedes
Posted: 13 Aug 2016, 22:37
by mrluke
http://www.f1technical.net/forum/viewto ... 57#p651157
mrluke wrote:Torque can be seen as the power of 1 revolution, bhp is the power delivered over time, the more revolutions per minute you have the more opportunities you have to increase your power over time.
Anybody want to own up for -1 this post? I can't see anything technically wrong with it and assume you just disagree.
Power = Torque x Rpm
Looking at a single revolution, Torque = Power/1 which matches my simple explanation above.
Once you look at a time period say 1 minute then Power = Torque x nr of revolutions per minute - matches my 2nd statement.
If you take Torque as fixed then the only way to increase power is to increase nr of revolutions per minute - matches my final statement.
Re: 2016 Mercedes AMG Petronas F1 Team - Mercedes
Posted: 13 Aug 2016, 23:08
by Jolle
mrluke wrote:http://www.f1technical.net/forum/viewto ... 57#p651157
mrluke wrote:Torque can be seen as the power of 1 revolution, bhp is the power delivered over time, the more revolutions per minute you have the more opportunities you have to increase your power over time.
Anybody want to own up for -1 this post? I can't see anything technically wrong with it and assume you just disagree.
Power = Torque x Rpm
Looking at a single revolution, Torque = Power/1 which matches my simple explanation above.
Once you look at a time period say 1 minute then Power = Torque x nr of revolutions per minute - matches my 2nd statement.
If you take Torque as fixed then the only way to increase power is to increase nr of revolutions per minute - matches my final statement.
You got the downvote probably because "the power of one revolution" sounds like a bad 90ies RnB song or because it's just wrong.
"The power of one revolution" is as best energy (a force over a certain distance). Torque is static, there is no travel involved
Once more:
Torque: force at a distance
Energy: force over a distance
Power: force over a distance in a certain time.
Re: 2016 Mercedes AMG Petronas F1 Team - Mercedes
Posted: 14 Aug 2016, 03:12
by wuzak
mrluke wrote:http://www.f1technical.net/forum/viewto ... 57#p651157
mrluke wrote:Torque can be seen as the power of 1 revolution, bhp is the power delivered over time, the more revolutions per minute you have the more opportunities you have to increase your power over time.
Anybody want to own up for -1 this post? I can't see anything technically wrong with it and assume you just disagree.
I did not downvote you, but there is an issue with what you say.
Torque is not power, so it cannot be seen as the "power over 1 revolution". bhp = brake horsepower, which is a measure of power, not the "power delivered over time".
The term
brake refers to the method of calculating power on a dynamometer. The brake is used to measure the torque of the engine while the rotational speed is also measured, the power being calculated from them.
In fact, energy is "power delivered over time". If you have X kW for Y seconds then you have delivered X*Y kJ of energy.
It is true that if you increase the rotational speed the power will increase for a certain torque, and can still increase even though torque falls.
There are some issues with your follow-on post:
This is the first mistake.
Power = Torque (Nm) x Angular Velocity (radians per second).
1 RPM = 2*pi/60 radians per second.
Power = Torque * (RPM * 2 * pi)/60
The problem here is that you need to be looking at angular velocity, not simple rotation.
For an angular velocity of 1 radian per second
Torque = Power/1
For a rotational speed of 1 revolution per second the angular velocity is 2*pi radians per second.
For 1 rps, Torque = Power/(2*pi)
Torque over 1 revolution gives energy.
For 1 revolution the angular displacement is 2*pi.
Energy = Torque * 2*pi
mrluke wrote:If you take Torque as fixed then the only way to increase power is to increase nr of revolutions per minute - matches my final statement.
Yes, this is correct.