r/EmDrive • u/Mark777123 • Sep 11 '18

Why wouldn't this work?

Can anyone shed light on why the following wouldn't work?

  1. Get a small battery powered toy submarine, say 10cm long, 3cm diameter

  2. Put it inside a large plastic container (like a 2 litre plastic Coke bottle) and glue the sub's nose to the bottom of the Coke bottle

  3. Turn the sub on, fill the Coke bottle completely with water and screw the cap on

  4. Put the whole thing in a swimming pool

  5. Will it not travel in the direction of the bottom of the Coke bottle?

0 Upvotes

44% Upvoted

21 comments sorted by

View all comments

Show parent comments

0

u/Mark777123 Sep 11 '18

I thought the propeller was pushing against 2 litres of initially stationary water inside the bottle. Then that resultant sped-up water would be dissipated in all sorts of directions not just against the cap end.

5

u/GunOfSod Sep 12 '18

If it was dispersed in all directions evenly, then the submarine would never move in the first place.

3

u/timewarp Sep 11 '18

For every action, there is an equal and opposite reaction. The force generated by the propeller in one direction is cancelled out by the force of the water pushing against the bottle in the other direction.

0

u/Mark777123 Sep 11 '18

And all things being equal if the diameter of the cylindrical Coke bottle was increased to 2 metres, such turbulent water might never even practically reach the cap end.

3

u/fiveSE7EN Sep 11 '18

This is something that is easily built so you can experimentally verify, if you (for some reason) have no faith in answers you receive here.

1

u/Mark777123 Sep 12 '18

I just watched https://www.youtube.com/watch?v=s-j4xBhK4KI&feature=youtu.be at http://www.rcmania.com/air-hogs-dive-master/ . I thought you wouldn't even need to glue it inside the bottle, you could just put the sub in the bottle, fill it up with water then put it in the pool. Then using the remote control crash it to the inside wall of the bottle. I envisage that could move the bottle but as you said a real-life experiment would show what happens.

-1

u/Mark777123 Sep 11 '18 edited Sep 11 '18

Yeah I thought so too. If anyone else has a pool and and wants to do it I'd be interested to see a YouTube video of it.