Something to think about

[selector]

The path that a point on a rim seems to take in planar space is called a cycloid. A point anywhere inside that circle (rim) will not be a cycloid because that point does not move at the same speed as the axle about which the rim turns...and which the loco moves. The motion relative to the ground is irrelevant because the rods aren't attached to the ground. They are attached to the wheels, and turn in circles with the wheels. The only force that the rods experience are acceleration away from the tangent to the rotation arc, minus a smaller vector when they are arcing away from the direction of motion of the axle along the track.

Any physicists out there?

[Anonymous]

Selector----- Even though the wheels and siderods are turning at a constant rate IN RELATION TO THE LOCOMOTIVE they are constantly changing speed IN RELATION TO THE GROUND. Try it with a model locomotive. I made this observation afer watching a video taken by a camera strapped to the siderod of Nevada Northern 4-6-0 number 40. Also in the movie "the General" starring Buster Keaton he is shown sitting on the siderod of an old 4-4-0 as it moves slowly along. BTW don't try that at home. Good luck getting to sleep tonight . Odd-d

[lionelsoni]

The side rods and the piston both move alternately a little faster and a little slower than the locomotive generally, but not twice and zero, because they are attached to the cranks no more than half the distance from the axle to the tire. However, there is a part of the locomotive that not only moves more than twice as fast but also briefly moves backward.

[Anonymous]

The rods need to move twice as fast as the loco. For every one revoution of the wheels, the rods go up and down.

[selector]

Sorry, I don't understand.

The rods move along the rails at the same speed as the loco, but also have tangential motion. They only pause and reverse their paths in appearance when veiwed from the side. It is the piston rod, in my view, that stops, and then accelerates back the way it came. But the side rods are moving in a constant circle.

[Anonymous]

Yes, Odd-d, you are correct

[Anonymous]

Here is something to waste your time thinking about. No matter how fast a steam engine is running down the tracks the side rods are constantly changing speed from dead stop to twice as fast as the engine is moving. Think about it: when the rods are all the way down they are not moving at all for the infinessimal moment then it speeds up to the top where for a lickering moment it is travelling twice as fast as the engine itself. Now I hope I haven't ruined anybody's sleep tonight as they lay there trying to visualize this. Odd-d