AdderMk2

a bullet has a three dimensional path of travel... a piston only goes up and down

Joel5.0

Fire the bullet at 90°....... will it stop before coming down?..... Check the position vs velocity graph below, check piston position at 0° + 360° and 180°... do you see the "dwell line"?

Li0nHart

the same rules apply if the bullet were fired straight up...gravity would be yanking it down even as it traveled up..once it reached maximum height it would instantaneously be pulled down...it would only pause if gravity stopped acting on it...which doesn't happen.

i used the 45 degree angle example as it is easier to visualize a bullet flying horizontally rather than just straight up.

AdderMk2

dude seriously, your ****ing wrong.

stfu and go away

Li0nHart

the bullet is basically traveling in two dimensions....it's path can be graphed easily on a flat sheet of paper.

to our eyes a piston only appears to go up and down...it is actually traveling in an elliptical path....hence the graph of it's motion is parabolic sine curve.

it is traveling in an oval that only has height but no width due to the piston being constrained by the cylinder wall.

if the cylinder wall were removed, the piston would travel in it's oval path being flung around by the crank....

it gets a bit interesting here....because if the piston is mathematically behaving as if it it traveling in an ellipse, then the piston doesn't really change direction when it travels...weird!!

Joel5.0

....do you know that in order to change velocity from + to -, or vice versa you cannot skip/jump over "0"..... simple math and physics. BTW... a bullet is a free falling body (and it too dwells), the piston is not. You may be able to visualize it better looking at this applet.

mjr46

if the cylinder wall were removed we would no longer have a motor!!!, and that's what we work on here and or build here, not rifles nor the bullets they fire.....while the physics and geometry of and engine can be interesting to contemplate......it still will not change the fact that the piston does stop at tdc to reverse it's direction, that theroy will always exist ..plain and simple whether you want to believe it or not .....as the saying goes I can lead a horse to water but I can't make him drink it

Li0nHart

i'd luv to see the graph of a dwelling bullet ...but then agian they did prove the single bullet theory on discovery channel one night..hehe

zero probably isn't the best word...rather the "origin". Zero on graph sits at the origin but the origin sits as a singularity at the exact center of Zero....it's impossible for us to imagine it as it sits at infinity.

The motion does not skip over the origin but it passes right through it as it would if it were traveling an elliptical path (mathematically is doesn't change direction).

the theory can be summed up in the following....

You will have to imagine that you are standing next to the fence at an elliptical track and viewing the car from a stationary point directly in front of you. It is easier to illustrate in the overhead position for clarity though... The car is also moving at a constant velocity.



At point A the car will appear to be at its maximum velocity as it travels to the right of you. Equivalent to the beginning of the upstroke of the piston.

From your point of view, the area indicated by point B would show an apparent rapid deceleration. Equivalent to the piston approaching TDC

At point C the car would appear to stop and reverse direction all in one instant. This is equivalent to TDC of the piston

At point D, the car is apparently moving at it's maximum velocity to the left of you (opposite direction). Equivalent to the end of the downstroke of the piston.

Since we know that the car was maintaining a constant velocity it was impossible for it to actually stop even though it appeared to do so. The car, in fact did not even change direction although it appears to have to our eyes.

The curve of the track matches the curve of the motion of the piston in an engine.

Now of course we can imagine the motion of a piston traveling up and down in the cylinder and we assume that this is a linear motion. It is in fact linear to our eyes, but mathematically, the piston is traveling in an ellipse and never changes direction. It is simply going 'round and 'round in an ellipse that has height but no width and it does not stop.

Jfsram

To further add to your confusion. You can make the piston STOP longer. Engine builders can change the dwell time with connecting rod length.

The debates between short vs long connecting rod. Piston speed, dwell time, side load, etc can go on and on and will go on as debatable topics until the day combustion engines are gone.

For what it's worth. Anything that goes up then down or down then up, did stop.

JD1969

All this talk of theory and graphs and such, what I want to know is this. What has the OP built? And how did it perform? Theory is great and all but if you cannot put it to use, it's not worth a damn.