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Thread: Experiment help - What is the card used for?

  1. #1 Experiment help - What is the card used for? 
    jr is offline
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    Join Date
    Sep 2009
    I wonder if anyone can help me. I am very new to physics so please excuse my limited understanding!
    I'm shortly planning to carry out some simple experiments which demonstrate how one form of energy can be converted to another. One of the experiments I'm intending to try is very similar to 'activity dyn 2' (pg. 3) on this link:

    The trouble is I have no idea of the purpose of the card attached to the dynamics trolley! Could anyone possibly explain this to me? The dynamics trolley I'm going to use has a card with a measurement of 10cm written on it. Since the length of the ramp I'm going to use is clearly longer than 10cm, would this measurement possibly represent the length of the trolley? (I have none of the apparatus at hand at the moment so am unable to check this). To work out the velocity of the trolley as it passes through the light gate, I've been instructed to divide the measurement on the card by the time taken for the trolley to pass through the gate. What is this card meant to represent?
    Am I corrrect in thinking that velocity is worked out by dividing 'the distance travelled' by 'the time taken'? Does this then mean that the measurement on the card is meant to represent the length of the trolley?
    Sorry if this is a silly question!

    One further question: Would air resistance/drag be a reason for the dynamics trolley to loose some kinetic energy as heat as it moves down the ramp or would any energy loss be entirely due to friction between the wheels and surface? Does air resistance only occur when there is wind?

    Many thanks,
    I'd be very appreciative of any help you may be able to give me!

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