Calculating Water Rocket Force: Velocity, Time & Mass

In summary, the force of a water rocket's acceleration is equal to the force of the reaction mass (water) being ejected in the opposite direction. The change in mass of the water can be calculated using the equation: change of M = area of exit x water density x (velocity of water x time). However, without knowing the velocity and time, it is not possible to determine the change in mass or the force of the rocket's acceleration. The acceleration of the rocket can be calculated using the equation: F = ma, where F is the force of the reaction mass. To accurately calculate the speed of the rocket, the speed of the water leaving the rocket must also be known. Increasing the air pressure in the rocket can result in a
  • #1
Db75
5
0
Hi,

I understand that the force with which a water rocket is accelerated is equal to the force of the reaction mass (or water) sent in the other direction.

If the change in mass of the water as it is being ejected can be calculated from this equation:

change of M = area of exit x water density x (velocity of water x time)

How am I supposed to find out the change of mass if I have no idea what the velocity and time is?

Do I have to compare that with the velocity of the rocket (which I know)?


Thanks
 
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  • #2
OK this is what I have now:

F = delta(mv) / delta t = (density x exit area x v^2)


But, I have no idea what v is.


I know that the acceleration of the rocket is equal to (v^2 / 2) / displacement, and so F = ma which equals the force of the reaction mass.

Hmm I may have answered my question..

But just so I know-

Without knowing the velocity of the water, there is no way I can work out the force..that would depend on the air pressure and all that...correct?
 
  • #3
I'm sure it has occurred to you that if you take exactly the same amount of water but increase the pressure in the rocket (by pumping air in) the rocket will move faster. Unless you have some indendent way of calculating the speed with which the water leaves the rocket you will not be able to calculate the speed of the rocket.
 
  • #4
Yes.
Thanks for your input.
 

1. How do you calculate the force of a water rocket?

The force of a water rocket can be calculated using the formula F = m x a, where F is the force in Newtons, m is the mass of the rocket in kilograms, and a is the acceleration in meters per second squared. The acceleration can be calculated by dividing the change in velocity by the change in time.

2. What is the relationship between mass, velocity, and force in a water rocket?

The mass of a water rocket affects its velocity and therefore its force. A heavier rocket will have a greater mass, which will require more force to accelerate. However, if a lighter rocket has the same amount of force applied, it will have a higher velocity due to its lower mass.

3. How does the amount of water affect the force of a water rocket?

The amount of water in a water rocket can affect the force in two ways. First, a larger amount of water will increase the mass of the rocket, which will require more force to accelerate. Second, as the water is expelled from the rocket, it creates a reaction force that propels the rocket forward.

4. How can the time and velocity of a water rocket be measured?

The time and velocity of a water rocket can be measured using a stopwatch and a measuring tape. The stopwatch can be used to time how long it takes for the rocket to reach a certain distance, and the measuring tape can be used to measure the distance traveled. The velocity can then be calculated by dividing the distance by the time.

5. What factors can affect the accuracy of calculating water rocket force?

There are several factors that can affect the accuracy of calculating water rocket force. These include variations in the initial pressure of the rocket, the amount of water used, and the angle at which the rocket is launched. Other factors such as wind resistance and friction can also affect the accuracy of the calculations.

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