Stopping a steam loco with a coin

Hi folks, new member here from Blue Mountains, Australia. I am a writer, and my current book features steam locos, and by way of research I was hoping that some of you folks in the know might be able to help.

We all know that a coin placed on a track in front of a loco will be squished into a flatter representation of its former self. However, I have heard the theory that a coin jammed tight between the track and the driving wheel of a stationary loco will render it immobile. I don't know if the reason is supposed to be that the grade between the top edge of the coin and the track is too great for the loco to climb, although I would have thought that the torque of a big loco would counteract that pretty easily.

Have any of you heard this theory, and is there any truth in it whatsoever?

Please help if you can -- I'd be very grateful.

Cheers,

James Roy

 

James Roy, welcome to the Trainboard ... I'm sure you will find a whole bunch of friendly folks here ... not to mention a bunch of rather squirrely ones too.

Regards your question ... I too have heard that stated. I can't address it directly in the context of railroading. However, in the context of the Apollo Moon program and the Saturn V launch vehicle, I offer this first hand knowledge.

The Saturn V (first stage) developed 7.5 million pounds of thrust, or 38,000,000 horsepower. Within the first 8 seconds after ignition, as the 5 engines were coming up to maximum thrust, the launch vehicle was held stationary, locked down to the launch platform by only four(4) two(2) inch diameter stainless steel pins. These pins were machined to fit tightly into clamps on the platform to tolerences of less than 1/10,000 inch to prevent any(!) motion. The physical principle involved was:

F(force) = M(mass) x V(velocity) (squared)

If the velocity of the launch vehicle could be held to Zero(0), then the force exerted by the pins on the clamps was also Zero, and the launch vehicle could NOT move! The instant the clamps started to release, the launch vehicle was allowed to move and the force exerted by the launch vehicle relative to the platform became enormous ... nearly 19 Thousand Tonnes!!!!!

I'm sure one of the Trainboard members who are familiar with locomotives can explain your question directly ... but I believe, as long as the locomotive wheel is held absolutely stationary by the coin, the same physical principles will hold true ...

 

Thanks for your prompt replies.

James

 

James, welcome to Trainboard, and thanks for posting that interesting question. Bill, if the locomotive drivers slipped, instantly rendering the coin into just another grain of sand on the track, I would think she would just start right up and march over that coin. Interesting--wouldn't it take TWO coins, one on each rail?

 

Have you tried to get the crews at the Zig Zag Railway to try it?

I reckon that if you had a coin that was made of a really strong metal (titanium, platinum or some such thing) than maybe. The resulting 'grade' could be too much to get the loco going - however, I suspect the coin would crush rather than hold the loco back.

 

James Roy, welcome to our family here on the TrainBoard!

Your information is partly true!

I learned in Science class taught by Maybry Miller, about the "theory", and we as a class tried it. It is NOT one coin though.

The statement made was this: "If a copper penny is pressed snuggly against the facing side of EACH of a steam engine's drive wheels and the rail head surface, the engine will be unable to proceed forward under its own power from a standing start."

The reason given: "The engine can not generate enough energy to lift its own weight at the designed leverage available."

But, if each penny is placed one inch AWAY from being tightly wedged, then the momentum of the engine's weight CAN assist the steam pressure allowing the engine to climb up over the pennies."

We went to the D K & S railway station and placed our pennies, using a knife blade to assure each penny was tightly wedged in place. Then the engineer quickly opened the throttle with the Johnson Bar full forward, and nothing happened except the pop-off valve blew from full steam pressure!

(The engineer was dumfounded!)

He made three tries, but failed to ride up over the pennies!

Then we used a gauge of sheet metal we had prepared, to place each penny at exactly one inch in front, so all would be equal, and he tried again.

The engine seemed to start to roll then it simply flattened all the pennies and passed by!

We each got our notes graded, and wrote up our reports. Our pennies were our proof of success. The first set showed a slight dent along one edge, the second set of pennies were of course flattened.

It was a great feeling to have made a scientific experiment that proved the fact!

I am not aware of whether this will work on a diesel or not, but I would suspect it would be the same.

 

Hello james, I am also new here and from Australia, welcome to trainboard. You posted and interesting question, the answers were also intersting. Perhaps i should go and test it out myself, it could be a good reason to go to the railway museum again

 

I tried this experiment with a diesel. It didn't matter whether I places the coin against the wheels or far away, it still shorted out the track and the diesel wouldn't run!

Welcome James Roy! The Blue Mountains. Beautiful place! I've had the privilege of visiting twice. Your countrymen are very polite!

 

BE ABSOLUTELY CERTAIN YOU OBTAIN RAILROAD PERMISSION BEFORE ATTEMPTING TO PERFORM THIS EXPERIMENT!

1. You will have to be on Railroad property.
2. You are well within the "killing zone" of powered equipment.
3. You must have the cooperation of qualified Railroad personnel to operate the equipment.
4. The engineer must fully understand what you expect to happen, or NOT happen in this instance, and he must agree to try it under safe conditions.
5. You must collect the coins after the experiment, as well as any other material and trash you carry onto the property.
6. you may have to be supervised by some railroad person in authority to prepare for, and during the performance of your experiment.

When we performed this experiment, our Teacher obtained the permission of the Railroad, made the arrangements to use an e gine for a few minutes, and was responsible for "crowd control" of his class around the engine. Most of us knew the engineer to begin with, which helped too.

It may not be possible to do this today, because of insurance problems.

You may also have to explain the law of Inertia before convincing the railroad people that this can be a valid experiment.

 

I understand the point re suspension equalizer system, but is this in the case of a steam or a diesel? And if it's a matter of inertia helping an engine "climb" over a coin, why wouldn't one coin be enough? Why would you need one on each track? If one wheel can't develop any forward motion, then neither can the other, surely.

Further, would it need to be the driving wheel? Wouldn't this experiment equally work on the leading wheels of a steam loco? The diameter is smaller, therefore the angle (or "grade" would in fact be steeper and more difficult for the loco to climb.

 

The point is, if you only use one or two coins, the engine CAN move over those because the entire weight of the loco is not required to be lifted. Only the small portion impeeded by the coins.

However, if coins are placed in such a position that the entire weight of the locomotive must be lifted inorder to gain any forward motion, then the loco will be prevented from moving.

With coins under EVERY driving wheel you are asking the engine to LIFT ITS WEIGHT up an almost 90 degree grade!

With only one or two coins under any one pair of wheels, then the equalizer system will allow that one wheel to raise up without lifting the entire engine's weight, thus it will proceed on.

Remember the law of inertia: "Things at rest, tend to remain at rest, and things in motion, tend to remain in motion."

You can try this with your car. fill your tires to only twice their rated airpressure so they are very firm. (They are rated at three times the stated air pressure when new.) carefully sweep an area in front of all four wheels to clear any rocks, and make sure it is dry and free of oil, sand, leaves etc. Also perform this out in a parking lot where if you happen to have one board spin out from under a tire with less air pressure than the other, you will not bump into another car, a building, or shoot off a cliff!

Now place a 2x4 tightly against each of the four tires. Start the motor, shift into high gear, and very slowly let out on the clutch while accellerating the motor. You will burn out your clutch or stall the motor before you get the car to go over the blocks.

If each 2x4 has been placed tightly against each tire, the car does not have enough horsepower to lift its own weight straight up.

That is also why cars have to have gears. You have to have a low gear to overcome inertia to get a car into motion, or slip the clutch in high gear with the motor running fast until it begins to roll.

(I will concede that a car equipped with an automatic transmission might climb up over the blocks, because it "automatically" shifts into a lower gear, which a steam engine does not have. That would not be an "apples to apples" test between the two, see?)

A steam engine has the total available horsepower to use at any point from start to wide open, it is always in "gear". If you tried to move your car in high gear with the clutch out, by simply turning the ignition, the car motor will stall out.

I suspect a diesel electric of today would not be able to raise its own weight either, because it would only build up a high amperage and not climb up the steep grade with a penny tight under every drive wheel.

It is simple Physics.