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AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread] Watch

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    (Original post by sykik)
    Can anyone explain why racing tracks are bunked in terms of centripetal force.
    It reduces the frictional force on the tyres as the horizontal component of weight will provide some of the centripetal force keeping the car on the track. If the ground was flat there would be no horizontal component of weight. .

    This means that you can go around a bend on a banked track quicker than you can when its flat

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    (Original post by _Caz_)
    It reduces the frictional force on the tyres as the horizontal component of weight will provide some of the centripetal force keeping the car on the track. If the ground was flat there would be no horizontal component of weight. .

    This means that you can go around a bend on a banked track quicker than you can when its flat

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    When the ground is flat how does frictional force provide centripetal force?
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    (Original post by sykik)
    When the ground is flat how does frictional force provide centripetal force?
    Frictional force on the tyres keeping the car in a circular path is the centripetal force


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    (Original post by Mehrdad jafari)
    Frictional force on the tyres keeping the car in a circular path is the centripetal force


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    But isn't centripetal force towards the centre? I donno i am getting confused like how can friction provide centripetal force?
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    (Original post by sykik)
    But isn't centripetal force towards the centre? I donno i am getting confused like how can friction provide centripetal force?
    No, you're not confused, your question is reasonable. The centripetal force is the force required to keep a body in a circular motion, whether that be the circular motion of the earth around the sun or a car turning a roundabout. A car cannot turn around a circle if there is no friction between the tyres and the road because bodies have the "tendency" to move in a straight line. So a car going around in a circle will need a force keeping it in its path and that force is the frictional force. Of course this force is acting towards the centre of the circle because that's how the frictional force is able to keep the car in a circular path.
    In fact if there was no frictional force between the tyres and the road (assuming it had some jet engine to power)and the car was attached by a string to the centre of the circle then the string would do the same job as the friction between the tyres.
    Is that quite clear?


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    Thanks it makes a lot more sense now.
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    (Original post by sykik)
    Thanks it makes a lot more sense now.
    No worries. I'm happy it helped


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    Guys, it's very awkward but last night i dreamt that i was doing phys5 paper and the six marker was the proof of the kinetic theory of gas equation. My mind may be subjective this time due to the lots of comments it has seen on here lol


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    (Original post by Mehrdad jafari)
    Guys, it's very awkward but last night i dreamt that i was doing phys5 paper and the six marker was the proof of the kinetic theory of gas equation. My mind may be subjective this time due to the lots of comments it has seen on here lol


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    I thought this too! But surely that would be to easy for a 6 marker ??


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    (Original post by gcsestuff)
    I thought this too! But surely that would be to easy for a 6 marker ??


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    But they've never asked this before, and all of the nuclear stufff has been exhausted. Plus nothing on gases for a while (unless they put in a question about thermal)
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    So it's either a thermal experiment, or the kinetic theory
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    (Original post by gcsestuff)
    I thought this too! But surely that would be to easy for a 6 marker ??


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    Well, not if it it was worth less than six marks. And also the derivation of the equation in the textbook seems quite wrong even though the final equations seems right.


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    (Original post by AR_95)
    So it's either a thermal experiment, or the kinetic theory
    What thermal experiment could it be?
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    Could someone help me with june 2013 question 1 part c? thanks a lot
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    Does anyone know of any solutions to the multiple choice questions?


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    Hi can anyone explain what should the angle be between. I came across a multiple choice question where they had given us a wrong angle and we had o workout the right one but i don't understand the angle should be between? Thanks
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    Just read that emf is always induced, but current only if the circuit is complete. Can someone explain this a bit? So if the coil was not all the way round, and had a gap, and you drop a magnet through it, will it take longer than if there is no coil?


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    Also, can somebody explain alternators from scratch? Including why it's so important we use AC, just everything that's going on there!


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    Name:  67.png
Views: 43
Size:  54.0 KB Hi I get why EMF is 20 but i don't get how you workout frequency ?
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    (Original post by chughes17)
    Just read that emf is always induced, but current only if the circuit is complete. Can someone explain this a bit? So if the coil was not all the way round, and had a gap, and you drop a magnet through it, will it take longer than if there is no coil?


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    The reason emf is induced in conductors is that charged particles move when in a magnetic field. emf is the potential difference - so the difference in charges - which you'll get in an incomplete circuit because charge will build up at one end due to movement of electrons. In a complete circuit, the electrons continue moving, so you get a flow of charge - a current.
 
 
 
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