wireman Posted July 25, 2012 Report Share Posted July 25, 2012 I just finished a lab that investigates the relationship between the mass and velocity of a water rocket. After plotting mass against velocity, I got an upside-down quadratic equation like graph. Even if I do make it a linear graph by altering variables, the gradient doesnt mean anything. The "product" of the two actually gives Momentum. What should i do? My teacher says I must plot the straight-line graph even if the gradient doesn't mean anything.Moreover, do i have to explain why 'X' mass gave the highest velocity? And do I have to explain in detail why the graph is how it looks like it is? I realised too late that this lab takes into account changing mass as time passes, which I don't know anything about. Reply Link to post Share on other sites More sharing options...
MLI Posted September 23, 2012 Report Share Posted September 23, 2012 actually i have no idea about the physics lab report since my teacher is the worst teacher ever, but do you think that you could do the experiment again? because maybe there was something wrong and you didn't notice 1 Reply Link to post Share on other sites More sharing options...
flinquinnster Posted September 23, 2012 Report Share Posted September 23, 2012 Well, our teacher says that we have to linearise all our physics lab graphs to straight lines. If you're getting an upside down quadratic, I would say that perhaps the equation that the experiment relies on is too difficult. Particularly since you said that you have a changing mass, and if you have two variables changing (mass and velocity) in momentum it may be too difficult. What's the quantity that you're trying to find at the end of the experiment? Usually you want to have a constant that you can find, as opposed to simply describing a trend. I don't know how much more help I can be, but if you want to post up the equations that you're using in the experiment, we might be able to give you more help 1 Reply Link to post Share on other sites More sharing options...
wireman Posted September 26, 2012 Author Report Share Posted September 26, 2012 Well, our teacher says that we have to linearise all our physics lab graphs to straight lines. If you're getting an upside down quadratic, I would say that perhaps the equation that the experiment relies on is too difficult. Particularly since you said that you have a changing mass, and if you have two variables changing (mass and velocity) in momentum it may be too difficult. What's the quantity that you're trying to find at the end of the experiment? Usually you want to have a constant that you can find, as opposed to simply describing a trend. I don't know how much more help I can be, but if you want to post up the equations that you're using in the experiment, we might be able to give you more help It's basically a water rocket launched at an angle of 23 degrees. Each time, the mass of the rocket is changed by changing the quantity of water in the bottle. Well, ideally, I do end up describing a trend, because I couldn't reach a solid conclusion as to why the velocity was the most for a certain quantity of water. I tried using concepts of impulse, air molecules, but was unsuccessful. Is it okay if I just describe a trend and finally state that when 33% of the bottle is filled with water, the velocity is the highest? Reply Link to post Share on other sites More sharing options...
Drake Glau Posted September 26, 2012 Report Share Posted September 26, 2012 The point to labs to find trends in the relationship between your two variables so I don't see why you would need to linerize any of them. If your graph displays how the velocity changes with respect to the mass of water in the bottle (not the %, the actuall mass that I hope you recorded ) then you shoould be alright.I have no idea how you would make this linear either... Reply Link to post Share on other sites More sharing options...
flinquinnster Posted September 27, 2012 Report Share Posted September 27, 2012 Well, our teacher says that we have to linearise all our physics lab graphs to straight lines. If you're getting an upside down quadratic, I would say that perhaps the equation that the experiment relies on is too difficult. Particularly since you said that you have a changing mass, and if you have two variables changing (mass and velocity) in momentum it may be too difficult. What's the quantity that you're trying to find at the end of the experiment? Usually you want to have a constant that you can find, as opposed to simply describing a trend. I don't know how much more help I can be, but if you want to post up the equations that you're using in the experiment, we might be able to give you more help It's basically a water rocket launched at an angle of 23 degrees. Each time, the mass of the rocket is changed by changing the quantity of water in the bottle. Well, ideally, I do end up describing a trend, because I couldn't reach a solid conclusion as to why the velocity was the most for a certain quantity of water. I tried using concepts of impulse, air molecules, but was unsuccessful. Is it okay if I just describe a trend and finally state that when 33% of the bottle is filled with water, the velocity is the highest?I have to say I'm not sure how the link is there between mass and velocity either - I would have thought impulse would be the way to go, considering m and v are in the equation. Maybe something to do with kinetic energy? If this is a DCP, I don't think it will be an issue, but honestly i think that writing a CE on this may be difficult. Reply Link to post Share on other sites More sharing options...
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