even MORE questions on engine physics

[dsjunkie]

ok well i was reading the big post by wherezmytofu (which i must say is good, you know your stuff man) and it brought up an old issue i had w/ a post a few days back on torque and power, the physics thereof....

torque is the dot product of the force applied and the radius of the object, and power is the dot product of the force and the velocity.

now i know the force is the force of the explosion of the air/gas mixture in the cylinder....and the radius is the radius of the crank...and velocity is rpms (but i'm not concerned w/ that right now....just the torque aspect of it)

ok the dot product has to do with vectors, correct?....example, the dot product of (u,v) and (x,y) is ux + vy, similarly the dot product of (u,v,w) and (x,y,z) is ux + vy + wz

now here's my question how do you convert a radius to a vector?

btw if you want IM me at dsjunkie...i'm on a lot (mainly at night)

[AceInHole]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (dsjunkie @ Mar. 12 2002,02:03)</td></tr><tr><td id="QUOTE">ok well i was reading the big post by wherezmytofu (which i must say is good, you know your stuff man) and it brought up an old issue i had w/ a post a few days back on torque and power, the physics thereof....

torque is the dot product of the force applied and the radius of the object, and power is the dot product of the force and the velocity.

now i know the force is the force of the explosion of the air/gas mixture in the cylinder....and the radius is the radius of the crank...and velocity is rpms (but i'm not concerned w/ that right now....just the torque aspect of it)

ok the dot product has to do with vectors, correct?....example, the dot product of (u,v) and (x,y) is ux + vy, similarly the dot product of (u,v,w) and (x,y,z) is ux + vy + wz

now here's my question how do you convert a radius to a vector?

btw if you want IM me at dsjunkie...i'm on a lot (mainly at night)</td></tr></table><span id='postcolor'>
it's just like trig, or converting to polar coordinates.

your radius would be the hypotenuse, and the angle of the crank would be your theta. &nbsp;finding the vector would be the x and y value of that triangle made from the raduis and it's angle with some axis.

the easiest way would be at 3 or 9 o'clock, where the unit vector would be [1,0] or [-1,0] times the radius.

[wherezmytofu]

ace is the place for the helpful hardware forks....sorry just had to say it.....
well u missed our wonderful torque debate in the zilvia chat (no me dont just talka bout bobbies and midget porn <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/sigh.gif" border="0" valign="absmiddle" alt=''> )
...any way, when u start to take about rotation and translation we do not use the cartision corrdinate system...you'll soon learn...or already have know that we use andular posision, seeing that you seem to have a physics..and im not a physics teacher...check out your physics book on the chapers on "rotation", and "rolling ,torque and angular momentum".....hope that helps....the book will explain better then most...cuz it has diagrams and alot of examples <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=''>

[maddindian]

Torque is a CROSS PRODUCT of Force and Length not a dot product.

Dot products form scalars
Cross products form vectors and torque is a vector (rotational vector).

Torque = Force x Length = Force*Length*sin<angle>

Hope that helps.

[dsjunkie]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (wherezmytofu @ Mar. 13 2002,09:27)</td></tr><tr><td id="QUOTE">ace is the place for the helpful hardware forks....sorry just had to say it.....
well u missed our wonderful torque debate in the zilvia chat (no me dont just talka bout bobbies and midget porn <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/sigh.gif" border="0" valign="absmiddle" alt=''> )
...any way, when u start to take about rotation and translation we do not use the cartision corrdinate system...you'll soon learn...or already have know that we use andular posision, seeing that you seem to have a physics..and im not a physics teacher...check out your physics book on the chapers on "rotation", and "rolling ,torque and angular momentum".....hope that helps....the book will explain better then most...cuz it has diagrams and alot of examples <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=''></td></tr></table><span id='postcolor'>
actually i took physics a year or two back and i still have a pretty good grasp on it but it sounds like i will have to get a hold of my best friend for the books which i will probably need....he's the engineering major, i'm the biology major :-)

[XylathaneGTR]

mmmm...Engine physiscs...
Im hopefully taking Mechanical Engineering at UWO (University of Western Ontario) in...a number of years...Hopefully gonna work for HKS <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=''>
But learning this stuff is annoying... <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/crazy.gif" border="0" valign="absmiddle" alt=':crazy:'> sometimes can give yah a headache

[dsjunkie]

yeah learning does suck but hey as long as you LIKE what you're learning it doesnt hurt your head as much &nbsp;<img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=''>

To find the torque, multiply the force from the combustion (which should be the pressure in the cylinder multiplied by the area of the piston face) by the radius of the crank to get an approximation. &nbsp;Of course, friction and compression in the other cylinders will counteract this torque. &nbsp;To find power, multiply the torque by the rotaional speed of the crank. &nbsp;Be careful with units, I think you'll need the rotation to be in radians/sec.

[AceInHole]

well... HP = torque x RPM / 5225 (or is it 5252??)

[William]

yeah it's 5252

[Gismo R]

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (dsjunkie @ Mar. 14 2002,01:03)</td></tr><tr><td id="QUOTE">ok well i was reading the big post by wherezmytofu (which i must say is good, you know your stuff man) and it brought up an old issue i had w/ a post a few days back on torque and power, the physics thereof....

torque is the dot product of the force applied and the radius of the object, and power is the dot product of the force and the velocity.

now i know the force is the force of the explosion of the air/gas mixture in the cylinder....and the radius is the radius of the crank...and velocity is rpms (but i'm not concerned w/ that right now....just the torque aspect of it)

ok the dot product has to do with vectors, correct?....example, the dot product of (u,v) and (x,y) is ux + vy, similarly the dot product of (u,v,w) and (x,y,z) is ux + vy + wz

now here's my question how do you convert a radius to a vector?

btw if you want IM me at dsjunkie...i'm on a lot (mainly at night)</td></tr></table><span id='postcolor'>
maddindian is correct, it's the cross product of the radius [r] and the force [F].
To convert the radius to a vector you use

r*sin(theta) for the Y value
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;and
r*cos(theta) for the X value.
&nbsp; (theta being the angle between the X-axis and r)

To covert to 3D (hence x,y,z values), life gets a little complicated. You would need two angles, one from the Y or X axis and another from the Z axis. But basically the same idea as in 2D.

The cross product of two vectors is basically the product of the magnitudes of the vectors times sin(theta), where theta is the angle between the two vectors.

So when talking about Torque, here is the equation.

T = F x r &nbsp; &nbsp; &nbsp; = &nbsp; &nbsp; &nbsp; T = |F| sin(theta) |r|

[maddindian]

See...Algebra is useful!! And all the kids in my class doubted the teacher! McDonalds for them!!! <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt=''>

[Gismo R]

yeah without algebra we'd be riding in our pimped out wagons pulled by our over-worked horses <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt=''>

[gman240]

Looks like we have some good physics talk going on here. this stuff does not look to bad. I hope I can totally grasp it when the time comes. Wanting to be an engineer and alot of the foundation is in these types of science courses