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Homework Help: Lab Exam: Help?

  1. Jan 20, 2005 #1
    Hey there.
    I'm currently taking grade 11 physics, and as part of our final evaluation, we have to perform an in-class lab. We're not given the procedure, just what we have to determine and a list of apparatus. I have a general idea of what to do, but I'd just like some confirmation if what I'm thinking is the correct interpretation, or any other thoughts/tips/whatever you may have.

    Purpose: To determine experimentally the relationship between the rate of flow of water through a narrow opening and the height of the water column.

    I'm assuming we're trying to prove Torricelli's Law, but I may be interpreting it wrong. If we are, I assume I'm supposed to set up a burette and record different times for different amounts of water to flow through the tube, which should be a regressive linear relationship, no?

    We're supposed to create two graphs: water height vs time, which is easy enough. The other one is water height vs weight of flow of water, so would the rate of flow be the volume of water used/time? What sort of graph should I expect for the second one, if you've done anything similar?

    Any other thoughts/tips/ideas you have are GREATLY appriciated. Thanks for your time!
  2. jcsd
  3. Jan 22, 2005 #2
    can anybody help?
  4. Jan 22, 2005 #3


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    You sound like you're on the right track.

    To get the experimental volumetric flow rate, i.e. L/sec, gal/sec, etc... you can simply get a graduated cylinder and read off volume readings at specific time intervals. That will give you a plot of flow rate vs. time. Weight flow, or mass flow will simply be volumetric flow multiplied by the density of the fluid. You will most likely need a second person to take the water column readings at the same time you take the discharge readings. That way you could do it all in one run. Or if it's just you doing it, take one reading one trial, and then the other reading the second trial. You just have to make sure you use the same amount of water.

    If you are indeed proving Torricelli's Law, then the velocity (and thus the flowrate) should be proportional to the square root of the water column height producing the flow.
  5. Jan 23, 2005 #4
    lol are u in konziolka's class or mr. potts class?
  6. Jan 23, 2005 #5


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    Ha ha,

    I'm in Mr. Pott's class.
  7. Jan 23, 2005 #6
    only thing that isn't right about torricelli's law is that in a burette.. the water drips down like in a sink.. the hole isn't facing out horizontally so water doesn't really travel any distance horizonally ? cos we used the burette in chem .. so i don't think the equation we have to get or calculations is very complicated. but iunno XD
  8. Jan 23, 2005 #7
    hey! i'm guessing this is byron? anyway, yup very confused about this as well and i agree, torricelli's law is always facing out horizontally versus the burette's water flowing out straight. but on the marking sheet it says that the relationship between height of water and rate of water flow is linear. doesn't this verify that they are directly proportional because as height of water increases, the rate of water flow increases? so the eqn should be the standard y=mx+b? so confused!
  9. Jan 23, 2005 #8
    ur confusing me more :tongue2:
  10. Jan 24, 2005 #9
    wouldn't the rate of flow be the same no matter how much water there is? so, the height of the water column doesn't really come into play because you're dividing the amount by time anyway, so it should all be the same rate?

    or am i totally wrong?

    my only question about this thing is what does "height of the water column"- does it refer to how much water's in the column, or does it refer to how far the column is from the ground?

    it's weird seeing all these people from my class in here. to be totally cheesy- great minds think alike.

    and i'm in potts' class. go us.
  11. Jan 24, 2005 #10
    tomorow all i am going to do ...

    set up the dam burette.... fill it with 50 mL of water, 40 mL. 30, 20, 10..... time how long it takes all those 5 different volumes to totally run out of the burette ....... and then somehow plot a graph and make relationships lol.

    anyone else gonna do something different? write what ur gonna do plz :D
  12. Jan 24, 2005 #11
    i think i'm gonna do something like that, except measure in metres, not litres. it's hard to calculate the flow of water using litres because there's that bit right at the end of the burette that you can't measure. so even though using metres to calculate rate of flow of water is technically incorrect, it's more accurate than using litres. i don't think it will matter than much because the density and viscosity of water isn't anything really out of the ordinary.

    other than that, i haven't decided yet.
  13. Jan 24, 2005 #12
    rate of flow of water is L per second isnt it? so maybe i will measure both height and volume ? lol
  14. Jan 24, 2005 #13
    jus incase anyone will reply to this msg.. this is how my data t able will look.. plz tel lme any corrections or suggestions :p

    trial 1 trial 2 trial 3 trial 4 trial 5


    time (s)

    rater of
    water flow


    i think there is something missin or i put somethin wrong Xd plz help lol
  15. Jan 24, 2005 #14
    I didnt read the whole discussion as i dont have time right now but it seems to me that Bernoulli's principle is also involved in this. The height of water in the column varies with the pressure.
  16. Jan 24, 2005 #15
    probably but i think this lab is very simple and basic... won't involve using any "laws" which we haven't learned :p i dont think they will expect us to learn a law by doing a lab unless they told us to research it :D
  17. Jan 24, 2005 #16
    blah my lab is tomorow so if anyone reads this ... uh ... what do u think this means

    relationship between variables stated as an equality, with slope represented as symbol k

    for equation 2: height of water vs rate of water flow ....

    do u make an equation ? XD if so how lol im not good at makin equations... cos the first one is jus "Height of water is directly proportional to the time"
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