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Gcse PHysics coursework practical help

  1. Dec 2, 2003 #1
    Gcse Physics practical coursework help needed.
    Hey guys, my topic is something like what factors affect how far a noodle pot travels when in a catapult. Frankly... I'm stumped. Any ideas whatsoever will help, i'm ok at physics but this has just gone and killed me. We have to use formulas and stuff i'm sure, but it's just shooting me in the foot wondering which ones!

    what factors affect how far a noodle pot travels when in a catapult..
    All i can think off is angle and distance pulled back. :/

    ANY help whatsoever on which formulae to use and how to use it. Seriously. Even any planning help. I got it today and i need to think of something for a practical day next week. Have a planning session so any quick ideas in the next 20 hours would be nice.
  2. jcsd
  3. Dec 2, 2003 #2


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    Its mass and its shape are also factors.
  4. Dec 3, 2003 #3
    Ok cool, i just got ot know more about it.

    Basically we take a chair. Attach 4 rubber bands together. Pull it back as far as you want (10,20,30 cm) and let it go. YOu have placed a plstic cylinder with 1n weights inside.

    This experimetn is basically that and i've decided to do
    1. How far the rubber band is pulled back.
    2. How many weights are in the container.

    Ideas on what to write about are really welcome, i'm not looking for you to tell me everything.

    OK, one question i'm really frusstrated on is which formulas to use.

    I have distance pulled, weights being pushed, distance they are pushed too and the newtons the rubber bands have been pulled back to.

    Should i use ohms law as a general formula (rough?). What formulas and how do i use them? Sorry but i'm seriously freaked out.
  5. Dec 3, 2003 #4


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    I don't know what good Ohm's law will do as that is to do with resistance in electrical circuits. Perhaps you meant Hooke's law? That would be a good start. We can discuss a little of the theory.

    What you can do is think of the average force acting on the rubber bands. When no force is applied to the bands, there is no extension. When a force F is applied, there is an extension x. You may know that

    Work Done = (Force) × (Distance moved in the direction of the force)

    But here the force is varying, so use the average force, or

    (0 + F)/2 = ½F

    So the work performed on the bands is ½Fx.

    This work performed on the bands is equal to the potential energy given to the bands.

    When the object is fired, this potential energy is transformed in to the kinetic energy of the projectile. So

    Work done = Potential energy of catapult = Kinetic energy of projectile


    ½Fx = ½mv2

    Where m and v are the mass and velocity of the projectile respectively.

    There is a formula from ballistics that gives you the range of a projectile. You'll probably be able to find this elsewhere on the internet. Neglecting the effects of air resistance, the range of the particle on level ground is

    Range = (v2sin(2θ))/g

    You can solve the energy equation above this for v2, if your skills of algebraic manipulation are quite good, and you can substitute that into the range equation.

    You may be able to investigate the differences between the theoretical value of the range and the actual measured value and determine the causes.

    (Rubber bands don't have a linear force-extension relationship so Hooke's law doesn't apply to them very well. I do seem to recall my GCSE physics teacher discussing the average force method to determine the kinetic energy of a projectile when fired with an elastic band, though.)
    Last edited: Dec 3, 2003
  6. Dec 4, 2003 #5
    Thanks Ad, and yes we do have that formula. So there really are many places to gow ith just one investigation. Wow. MY physics teacher told me that hookes law (now ohms :)) was a good rough guide. That ballistics formula is going to give me some top marks but could you give me an example of working with some formulas with the information.

    newtons pulled back (rubber band)
    length pulled back
    Distance the egg shell thingy was fired.

    Kinetic energy: .5 * mass (meters)* velocity2

    Work done: Average force * Distance

    Energy transferred: Power * distance / Work Done

    Efficiency: Output/Input * 100 = percentage

    Most appreciated. These forums seem nice and even though i'm just a Gcse student i think i'll stay. :)
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