# Thread: Will these vehicles run? A puzzle from the past

1. ## Will these vehicles run? A puzzle from the past

2. The first one will tend to roll forward; the second one won't.

3. Wouldn't the second one move since there is a continuous stream of water to propel it forward? Once the lead ball left the trough, there would be no force to act on the vehicle, right? (looks like the trough is not touching the ground)

Science > SolitaryPenguin, so I am just guessing.

*edit*

I take that back, the water isn't hitting the ground. I am stumped then.

/wanders off to eat cake

4. Originally Posted by oberon
The first one will tend to roll forward; the second one won't.
+1

Edit - Assuming the vehicles are on flat surfaces.

5. I'm inclined to agree with Oberon on this one. Part of the gravitational energy pulling the lead balls down will transfer into forward motion due to the 45 in #1. #2 on the other hand, though the water is coming out of the hose, the force created is being negated when the water hits the reclaimer.

6. the 'equal and opposite reaction' that would propel the first vehicle is the movement of the lead balls out the back... the water-based vehicle does not have any gross kinetic output because it is a "closed loop"

7. The second method could be akin to thrust vectoring, if only more pressure were used, and the water were shooting backwards after hitting the ramp. As built though, I don't think it's going anywhere.

8. Am I a bit retarded for thinking that the first one's balls would just roll down that ramp onto the ground?? I don't see how it makes the car move.

9. Originally Posted by kyuuei
Am I a bit retarded for thinking that the first one's balls would just roll down that ramp onto the ground?? I don't see how it makes the car move.
Well, when the ball hits the 45 degree ramp, falling down, the ramp will cause the ball's direction to change (from straight down, as gravity pulls it, to partially horizontal), forcing the ball to move away from the back of the truck. Since the momentum of the overall system (balls + truck) must stay the same (ignoring friction losses, etc.), the truck will move forward as the released ball moves back. But it won't move much (assuming the mass of each ball is pretty small compared to that of the truck + balls still in the hopper). Assuming you're the person who has to pick up the balls and reload them into the hopper, you'd be better off just throwing them all away and pushing the truck by hand.

Oh no... I sound like my old physics teacher...

10. Haha... I am pretty sure that none of them will actually move more than a few centimetres.

The first one might tned to move forwards, as kelric said, because the momentum has to stay the same, but I think the vehicle is way to heavy to actually move.

The second one...well, I don't think it will move. I mean, the water is getting back from where it has left and besides, it's not even directed horizontally.

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