Flatening a penny on a railroad track

If I put a penny on an RR track and a train runs over it, it’ll be a thin piece of metal when it’s over. I’ve seen kids do this. I may have done this myself as a youngster, but being retired, I don’t remember that far back.

So, how much energy does it take to squish that penny? If I took 10 rolls of pennies (500 total) and laid them on the both tracks every foot for 249 feet, would the train’s speed diminish noticeably?

For starters, a US penny made after 1982 is 97.5% zinc. The other 2.5% is in its copper plating, but I think you can focus on its zinc makeup for malleability.

Every once in awhile I still see those penny smashers (excuse me, “coin operated manual crank penny press machines”) that stamp the logo of that particular tourist trap, so the energy needed is small enough that it can be supplied with a few pulleys and gears an 8-year old can handle.

These guys claim their penny smashers deliver 22 tons of pressure. I found one cite for a locomotive engine that says it weighs 134 tons.

I did this when I was dropping off my dad to Amtrack a few years ago. When the train struck the coin, both guys in the cab glared at me.

About 10 years ago trying to be the cool uncle when I tried this, I put the 6 or 7 coins I had in my pocket a few feet apart down the length of a rail. After the train passed we searched and searched, and finally found one flattened coin several feet away.

I reccomend glue or duct tape for field tests.

A fun thing to do is pick up the penny as quickly as you can after the train has passed. It will be quite hot (even on a cool day) from the work required to mash it out.

If you use scotch tape, they’ll (usually) stay on the track, but then your coin will have lines from the tape edges.

Every get a cent out of a commercial type clothes dryer? Its edge is rounded off and thickened. I found my second one last week.

It also depends on what alloy the coin is made of. Recent Camadian coins, for example, are all made of plated steel, so they probably wouldn’t squash as well as original copper pennies.

How is that possible? How can they glare at you when the train hasn’t squished the coin yet?

Well, if Seamus McFly and Dr. Emmett Brown are the engineers . . .

I remember being told this could derail a train, but I always thought it was just a ploy to get us kids to stop doing the coin trick. Any chance it could actually happen?

It causes more wear on the wheels (trucks) and they are expensive and time consuming to replace. They want to have a long life on them. Same with the rails.

If you stack a few coins on the rail, they will flatten out and fuse together, for maximum fun.

I once put a whole dollar on the rail.

The wind blew it away before the train ever got there.

They probably don’t want people running out to the tracks to place coins just before the train rolls past. Hitting people causes a lot of paperwork (glib answer) and is very traumatic for all involved (serious answer).

The coins aren’t going to have any effect on anything rolling on the rails, from a scooter to a heavy freight train.

A standard part of the tourist ride on the Eureka Springs and North Arkansas Railway is flattening coins on the rails - passengers de-board at the wye at the end of the line, and while the train is turning around, the conductor and guides tell people how to position coins for flattening. They say the secret is a goodly amount of spit. The coins are still quite hot after being flattened. Showing people this way is good - everybody gets their coins placed and then the train starts moving, so everybody is safe.


I don’t know how much energy it takes to flatten a coin. But I can tell you it takes a lot of energy to shrink one.


Using the work-energy theorem, with some back-of-the-envelope estimates: An intact penny is just about 1 mm thick, and a flattened one is maybe a quarter of that. So we’re applying a force over a distance of 7.5e-4 m. Using the figure of 22 tons for a penny-smasher (which is going to be comparable to that from a train car, since not all of the weight is on one wheel), we get about 220000 newtons for the force. That gives us a total energy of 2207.5e-4 Nm, or 165 J. For comparison, this means that if the handle of the smasher moves about 8 m (that’d be four full rotations, with a handle about a third of a meter long), then the person turning the crank must exert a force of about 21 N (about 4.6 pounds), which isn’t too unreasonable.

I have done this a few times in the past and I’m pretty certain there are two things I can tell you about it:

  1. It’s a waste of money.

    … and …

  2. It’s a waste of time.

But if you get some fun out of doing it, then go ahead and knock yourself out.

Just be careful that you don’t hurt yourself.

I have never heard of anyone hurting themselves. But there must be some danger involved somewhere somehow.

Post by Chronos (btw, one of my favorite incarnations)

This right here is one of the reasons I love this site. Actual data presented in a way that’s fun and entertaining for all. God you people are awesome.

and on topic, I’ve flattened a few on the ol’ tracks in my day and the biggest problem is just finding them after the train has passed by.