# Energy in scuba tank moving a car?

1. May 16, 2010

### rc777

I've watched the videos and read a lot of posts on here about compressed air storage.

I read that a filled scuba tank has over a million joules?

I'm trying to visualize what happens if you suddenly release all the energy from that tank,
it should be enough to move or brake/stop a sizable car?

example I had read was a 1200 kg car going 20 m/s needs 24000 newtons to stop?

so, a scuba tank has enough energy stored to stop this 1200kg multiple times ?

if that same 1200kg car is at rest, and you wanted to vent the tank to try to move it
if you vent it slow enough, you wont overcome resistance and will empty the tank without
it even moving?

If I vent the tank in an instant how do I calculate how far the vehicle is pushed?

If I vent slower, say 5 or 20 seconds, how do I calculate how that effects the distance a vehicle is pushed.

Thanks for any explanations, I've been reading and not really understanding.

2. May 16, 2010

### mgb_phys

A 12l scuba cylinder at 200bar (3500psi) stores about 1200KJ (0.35KWH) if the air is released to 1atm.

3. May 17, 2010

### rc777

Ok, 1200kj or 1.2 million joules. Can you help me with what some real world task might help me

visualize how much that is?

... for example how far it could push a car or other object, etc if expended all at once?

thanks!

4. May 17, 2010

### mgb_phys

A teaspoon of gasoline contains about 1000KJ of energy.

A small 100HP engine is 75KW, so a 0.35kwh tank would run it for about 15seconds (assumign 100% efficency)

5. May 17, 2010

### phyzguy

Well, a horsepower is 746 Watts, so a car using 10 horsepower (fairly typical for cruising) is using about 7kW. So the 0.35 kWh in your scuba tank would drive a car for .05 hours, or 3 minutes.