WATER ROCKET RESEARCH // 04.04.22
A water rocket typically consists of a plastic bottle, fins and some sort of cone for the head of the rocket, these individual parts all have there own part to play:
- The bottle itself obviously creates the body of the rocket but also stores the water needed to launch the rocket as when it is filled with air and that same air fills up the other 2/3rds of the bottle, when released all of the pressure from the bottle forces the water out of the bottle therefore propelling it.
- If the rocket wants to keep stable while its in the air then it is going to need fins, these can simply be made of cardboard and then stuck to the bottle body, as the rocket will exert a great amount of force to lift of the ground so carrying that momentum effectively is very important.
- And finally the cone acts as an effective way to control the direction of the rocket and increase speed as creating a cone or surface that greatly reduces drag will mean the rocket will travel further and faster but also when thinking about how light the rocket will be once in mid-air the cone should act as the weighted feature so as to keep the rocket unaffected by slight winds / jolts.
OUR ROCKET
This is my teams rocket that we ended up using in the final launch and you can see that the top of the rocket is not only weight with a tennis ball but also streamlined and designed to reduce drag through the use of smooth curved surfaces.
For more info on how this was made and a video of the launch click here
WATER ROCKET PHYSICS
When thinking about how a water rocket can be most effective one has to take into account the forces at play and how to maximise and minimise when needed to. In terms of the flight path of the rocket it all starts with the thrust. This is overall dictated by the ratio of pressurised air to water and the PSI of the pressurised air, the ideal amount of water would be just above 1/3 of the bottle too. With this sudden acceleration, it only lasts for a short amount of time before the rocket starts to rapidly decelerate, the two main forces are drag and weight, where gravity is -9.8ms^2 downwards. The weight component therefore is highly dependable on the amount of water left after the release of the rocket as (Weight = Mass x Acceleration due to Gravity) meaning the greater the mass the less the thrust will be. When it comes to the point where the rocket is at a coasting ascent and reaching maximum altitude the fins become a big deal as all objects are subject to gravity’s 9.8ms^2 acceleration towards the ground and so all should theoretically hit the ground at the same time?!
The only difference is air resistance and the ability to ‘glide’ meaning the more control our rocket has when at its peak is another important factor when it comes to getting the greatest distance, hence why many ‘professional’ rockets will also have parachutes.
This video from Brian Cox helps to elaborate and show how the only difference in time to fall is air resistance rather than weight:
REFLECTION
With the water rocket project its something that theoretically speaking is something that I find really interesting as it plays into my previous A-Levels those being maths and physics as well as product design. That being said I really enjoy the aspect of considering all of these different factors in play and tiny tweaks can have vastly different outcomes and the general fact that this is just a naturally fun practical project, in terms of what I’ve learnt, I’d say I’ve learnt about what its like to consider multiple perspectives on a given project and how to compare and contrast ideas when it came to the design of the rocket.