Will These Vehicles Run? (May, 1932)

$10 for the best Letter Answering the Question:

Will These Vehicles Run?

HERE’S a real brain tickler for puzzle fans—study the drawings above, figure out whether the lead balls and the water motor will move the vehicles or not (and why), send in your less than 300 word letter giving your reasons, and you may be rewarded with a check for $10.

Somebody’s bound to win that $10 check; it might just as well be you. There are no hidden tricks in these drawings. All you need is an understanding of natural laws. In addition to the $10 award for the best tetter, all other letters published will be paid for at regular space rates.

Keep your letter under 300 words, and be sure to mail it before May 15, 1932. Address letters to the Freak Vehicle Editor,

Modern Mechanics and Inventions, 529 S. Seventh St., Minneapolis, Minn.

Don’t fail to tell why the vehicles will or will not run. Here is the problem:

A vehicle carries a number of heavy lead balls, on its roof, which fall off the end of a trough and strike a second trough, mounted at a 45 degree angle at the rear of the car. Will the falling of the balls make the vehicle move?

The second vehicle is similar to the first, except that water is used instead of lead balls. The water is pumped against the trough by a motor, is retrieved in a funnel after it has passed down the trough, and is used over again. Will the water power move this vehicle?

  1. nlpnt says: December 16, 200812:09 am

    Hello, Mythbusters?

  2. Eamon says: December 16, 200812:54 am

    No. No they will not.

    Equal and opposite reactions, and all that. Well, the first one might give a little push but not enough to overcome the weight of the truck.

  3. Myles says: December 16, 20081:27 am

    If the staff of these magazines can think out the problems of propulsion, reaction and conservation of energy above, why do they publish the idiotic flying machines 🙂

    I think the lead balls might give the vehicle a small push. They have potential energy stored in their height, and they are leaving the system. Would they not be sort of like expelling rocket fuel?

  4. Casandro says: December 16, 20081:37 am

    The first one certainly works (unless the car is designed badly) as the balls will give it some impulse. It’s essentially the same pricible as with a rocket.

    The second one also moves. As some of the impulse of the water gets transfered to the car.

  5. Rick Auricchio says: December 16, 20081:52 am

    The lead balls work—and nobody tailgates.

    The water truck does not move. Though the falling water pushes the truck slightly forward, that energy is absorbed by the catch-basin moving the water toward the pump. The falling water kicked the basin forward, which was full of water already. So the basin’s expending energy moving the mass of the water forward toward the pump.

    If the water were expelled overboard like the lead balls, it would work.

  6. Casandro says: December 16, 20082:03 am

    Yes, but Rick, the speed of the water beeing catched in the basin is far smaller than the one of the water falling onto that ramp. Therefore the backward impulse is far smaller than the forward one.

  7. Mike says: December 16, 20086:57 am

    If it works or not I am sure these are included in part of the bailout money for the automakers.

  8. don says: December 16, 20089:30 am

    What were the Freak Vehicle Editor’s answers? We must know!!

    Dang; it doesn’t even say what issue they were planning the answers to appear in . . . .

  9. George Trudeau says: December 16, 20089:35 am

    Assuming an easy to move truck, lead balls yes, water no (though the pipe may rise up slightly).

  10. William Deering says: December 16, 200810:18 am

    The second one will work if a lost thristy bear attacks it from behind!

  11. William Deering says: December 16, 200810:25 am

    The second one will work if a lost thirsty bear attacks it from behind.

  12. JM says: December 16, 200810:42 am

    And the winner is… … … … ¿?

  13. Mark says: December 16, 200811:52 am

    The second one should work because the gas engine pump is injecting energy into the equation. The forward motion would be awfully slight though.

  14. Rick Auricchio says: December 16, 20082:06 pm

    The water can’t work.

    1. Yes, the falling water imparts a forward push because it hits the ramp.

    2. The fallen water now hits the basin while moving backward. The basin must impart a forward push to the water to direct it into the return line.

    Result is that the forces cancel out, because all the water is retained.

    As for the pump adding energy, we’re not talking about perpetual motion. What counts is the result of the forces.

  15. Rick Auricchio says: December 16, 20082:24 pm

    Here’s a picture showing the forces. The green foward force is balanced by the red rearward force.


  16. Raoul Duke says: December 16, 20084:46 pm


    some amount of water will be leaving the system, i’d claim. it might be only a super small amount, but some will. so there is some motive force, although presumably never enough to overcome the rolling friction of the tyres.


  17. Rick Auricchio says: December 16, 20086:10 pm

    @Raoul: Yes, water that bounces aft of the catchbasin will provide forward motion. So, technically, only 99% of the water must be moved forward by the basin; the other 1% that splashes off the back of the truck will provide a miniscule amount of forward motion.

  18. John says: December 16, 20087:29 pm

    1 will move 2 will not by conservation of momentum

  19. jayessell says: December 17, 20081:12 pm

    For #2, imagine a large bicycle chain instead of water, and a motor instead of a pump.
    Reguardless of which direction the chain moves, no energy is imparted to the truck.
    (Unless that chain is attached to an axle!)

  20. Churba says: December 17, 20081:26 pm

    Oh, they’ll both move. Just not move forward.

  21. person1 says: December 20, 20086:25 am

    the water one will work. Although, why not just make it a closed system….

  22. Joel says: December 27, 200812:40 pm

    The energy from the falling lead balls impacting the 45-degree trough will exert substantial pressure downward and forward. The majority of the force will come from the actual moment of impact which may be strong but so short in duration it is not likely to move the vehicle more than an inch or two (if that) per ball.

    The majority of the force created by the pumped water would be at the nozzle and push upward, opposite the expelled water. If the vehicle moved anywhere, it would go up in the air and that is not going to happen. The water would also have to be at such a high pressure that 1) most of it would rebound away in an intense but fine splatter or spray and 2) the recovery system returning the water to the pump (apparently gravity fed) would not be able to keep up with the volume of water.

  23. Frank Stallone says: December 27, 20082:46 pm

    The second one will work if a thirsty bear attacks it from behind!

  24. Ryan says: December 27, 20082:56 pm

    1. The lead ball car will work. Slowly. Conservation of momentum states that total momentum of a system must be conserved (assuming no external forces). No one can doubt that the lead balls will exit the car traveling in a rearward direction. This is momentum in one direction; to balance this to the zero momentum of the original system, the car must move forward at a rate proportional to the ratio of the ball’s mass to the mass of the rest of the system. This is the same basic principle as rocket propulsion.

    2. The water car will not work. Again, this can be explained using conservation of momentum. The water in the system never leaves (for the sake of this argument, let’s say all water is retained and nothing splashes out). All the momentum of the water is canceled by the rest of the water system since it is moving in a circuit. The motor powering the water circuit will impart energy into the water system, but this energy is used only to accelerate the water, or keep it at a steady rate to overcome friction forces in the pipes. The motor is not imparting any energy to the road in any manner, and no mass is being ejected from the system. Therefore, laws of physics state that the car will not move.

  25. Dave says: December 27, 20083:45 pm

    They will both work.

    A. The downward momentum of the lead bslls will deliver angular force to move the vehicle forward. The original location of theballs is irrelevant. Movement will depend on veihicle weight vs. ball weight and drop height.

    B. The water will transfer kinetic energy to the slide at initial impact. It will transfer reverse energy at the funnel, but this will be a smaller amount due to reduced kineitc energy resulting from initial impact. Pump pressure will ultimately determine movement or lack thereof based on same essential factors above.

  26. myk says: December 29, 200811:40 am

    First one moves (it’s a low impulse rocket, accelerating it’s ‘fuel’ (lead balls) by
    means of gravitational potential energy (from the distance they fall)

    Second one does NOT move. There is no momentum transfer (the circulating
    water can be considered as no more than an odd-shaped flywheel)

  27. Toronto says: December 29, 200812:18 pm

    Myk: Actually, I think the second one *would* move.

    Think of the slanted trough as a single-bladed turbine. It doesn’t matter if the system is closed or not, the motor is impelling the water against the ‘turbine’ and it ought to be able to harness some of the energy. Horribly inefficiently, of course, but possible.

  28. Ryan says: December 30, 20081:14 am

    Toronto: What happens when the water is captured by the return and then pushed in a forward direction? All momentum is canceled in a closed system. It will not move.

  29. The Clashing Blade says: January 1, 200911:00 am

    Neither are economicaly viable,the price of lead being in excess of £3500/tonne and water at £42.75 per cubic metre.

  30. Texas Jim says: January 1, 20099:30 pm

    I say the 1st one will move and the second one won’t.

    The bigger issue is what percentage of the energy used to operate the systems is wasted? I guarantee the effort it takes to load and launch the lead balls, or to operate the pump on the 2nd car, would move the car much more effectively than the systems shown.

  31. Texas Jim says: January 1, 20099:32 pm

    And I will be happy to sell Clashing Blade as much water as he wants for 32.75 per cubic metre.

  32. Mehmet ARI says: January 7, 20095:59 am

    Both will move, because energy is delivered to the system (car) from out of it. So there is some kind of fuel in both of the systems. For example, somebody lift and puts the balls onto the car, means charges the car with his energy. It is the same also in the second one working with water. Theoratically 45 degree board will work and create a forward push. Theoratically both cars will move.

  33. Pedro says: March 24, 201110:53 am

    The center of gravity of the entire system will allways stay the same, so, as the second figure is a closed circuit, the car will not move as no watter is moving away from the car.

    If the lead balls are moving away from the car, and the gravity center does not change, the car must move forward, away from the balls and away from the gravity center of the system (Cars plus balls)

    q.e.d: First Moves, second Not! Gimme my 10 bucks! 😀

  34. jayessell says: March 26, 20113:13 pm

    Congratulations Pedro!
    Climb into your Time Machine and claim your prize!

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