Physics question re: water rockets

[figleaf]

Homework question I can't answer.Hope one of you can help . If you pumped up and fired off a water rocket on a hot day and it flew a particular distance, would it go further or less far on a cold day?

I think it should be the same as it will only fire when the pressure inside the bottle is high enough relative to the pressure outside. The relative forces on the bottle have to be the same. This is just a guess though

what are they studying at the moment?
there is probably a clue there...

Energy, Forces ect muddleduck. I quite like your answer witchwithallthetrimmings - clever

I imagine the gist of the question is that on a hot day, the pressure inside the bottle will be higher, and so the bottle will fly further.

In practice, it won't make any difference because you pump up the bottle until it reaches a certain pressure anyway. It would only be if you were then to leave the bottle to stand for a while (which you never do).

Ooh, tricky one. I don't think you could say for sure either way.

When it's cold both the air and the water is more dense so the rocket will be heavier for a given volume of water. There'll be more outside air resistance, too, for the same reason. And the bottle will be less elastic so it won't expand as much when the air is pumped in so there'll be a smaller volume of air in the bottle before the pressure is reached.

On the other hand, though, as the air and water in the bottle will be more dense they'll impart more impetus when they are shot out of the back of the bottle. And if the day was too hot then the bottle will get too soft and lose its elasticity. And the heat won't do the rubber bung any favours, either.

It'll be a fascinating experiment to carry out, though. Let's do it!

My sons class are doing this on Thursday (after having done it in September)so I'll report back.

Don't forget, the rubber's softer at higher temperature, isn't it - so the pressure will be lower to push it out. So less far.

• I guess.....

Please tell us when you know - I'm really curious now.

Blimey, I have a masters in physics and I haven't got a clue! Too many factors I think. And I've forgotten everything I ever knew too.

Is this Rocket Science