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# Edexcel A2 Physics Unit 5 'Physics from Creation to Collapse' watch

1. Can anyone explain to me HOW Hubble's constant is changing due to gravitiational forces. Is it getting less? Why?
2. (Original post by havinghoops)
Can anyone explain to me HOW Hubble's constant is changing due to gravitiational forces. Is it getting less? Why?
Greater gravitional forces, reduces the rate of expansion and if the critical density is reached or surpassed, expansion would stop or universe starts to contract. hence greater gravitional force reduces receding velocity of galaxies hence reduces hubble's constant.

someone correct me if I'm wrong.
3. (Original post by Kameo)
Greater gravitional forces, reduces the rate of expansion and if the critical density is reached or surpassed, expansion would stop or universe starts to contract. hence greater gravitional force reduces receding velocity of galaxies hence reduces hubble's constant.

someone correct me if I'm wrong.
Sounds right to me
4. How can I get edexcel pastpapers 2005? PLEASE?
5. when it says define SHM, you say something like

restoring force of an oscillating system is directly proportional to its displacement which is in the opposite direction to the force. ?
6. (Original post by Kameo)
when it says define SHM, you say something like

restoring force of an oscillating system is directly proportional to its displacement which is in the opposite direction to the force. ?
pretty much yea, those Q's are always worth 2 marks.
1 mark for) The restoring force is proportional to the acceleration/displacement.
the other for) Restoring force acts in opposite direction to motion/ tries to restore oscillating object to equilibream position.
7. (Original post by havinghoops)
I'll tell you how to do it anyway, just incase they do ask. Something like what I've got on the diagram I've attached will be enough I think.

This is the exam I am freaked out about the most. Got no idea what they're going to throw our way.

Worried that I'm going to have put this much work in only to fail because I panic or the questions are so left of centre.
Cheers dude, I remember doing this experiment in class actually now that you've shown me it.

Still need this answered if anyone can <_>

Oscillations section;

My book says

If there is damping, then the resonant frequency at which the amplitude is a maximum is lower than the natural frequency, and that this difference increases as the degree of damping increase. However, the maximum energy transfer, or energy resonance, always occurs at the natural frequency.

The bit in bold I don't get. Surely when there's maximum energy transfer, the amplitude is going to be at its greatest meaning it should occur at the resonant frequency, not the natural frequency (where the amplitude isn't at its maximum when there's damping).
8. People,

Do we need to know what nuclear fussion,fission is?What weak/strong interaction is?

In the hodder book it does not mention anything.
9. (Original post by fredbraty)
People,

Do we need to know what nuclear fussion,fission is?What weak/strong interaction is?

In the hodder book it does not mention anything.
Yes Nuclear fusion is when two lighter nuclei form together to form a heavier nuclei which has a higher binding energy per nucleon than of that of the two nuclei. Energy is released because not all the energy is used as binding energy.

Fission is when a heavy nuclei splits into at least two lighter nuclei. Energy is released because the two lighter nuclei have a greater binding energy per nucleon combined than the parent nuclei.
10. (Original post by Kameo)
Yes Nuclear fusion is when two lighter nuclei form together to form a heavier nuclei which has a higher binding energy per nucleon than of that of the two nuclei. Energy is released because not all the energy is used as binding energy.

Fission is when a heavy nuclei splits into at least two lighter nuclei. Energy is released because the two lighter nuclei have a greater binding energy per nucleon combined than the parent nuclei.
Oh really?Thanks ,i wonder why hodder doesnt mention it.

11. (Original post by Sasukekun)
However, the maximum energy transfer, or energy resonance, always occurs at the natural frequency.[/i]
IDG what's confusing.

Resonant frequency occurs when the driving force matches the natural frequency of the oscillating system.

So for resonance:

driving force = natural frequency

So, this is where there is maximum energy transfer.

And thanks Kameo for answering my question.

abby'sthe best - what units are you looking for? You won't find past papers for unit 5.
12. (Original post by fredbraty)
Oh really?Thanks ,i wonder why hodder doesnt mention it.

I don't think you need to know that in detail: Just stuff from particle physics Unit 4:

Weak nuclear forces - beta decay

strong nuclear forces: not felt with leptons, but keep nucleons together
13. (Original post by unamed)
I don't think you need to know that in detail: Just stuff from particle physics Unit 4:

Weak nuclear forces - beta decay

strong nuclear forces: not felt with leptons, but keep nucleons together
awww many many thanks!That's what i thought too.
Best of luck tomorrow my friend!
14. (Original post by Sasukekun)
Cheers dude, I remember doing this experiment in class actually now that you've shown me it.

Still need this answered if anyone can <_>

Oscillations section;

My book says

If there is damping, then the resonant frequency at which the amplitude is a maximum is lower than the natural frequency, and that this difference increases as the degree of damping increase. However, the maximum energy transfer, or energy resonance, always occurs at the natural frequency.

The bit in bold I don't get. Surely when there's maximum energy transfer, the amplitude is going to be at its greatest meaning it should occur at the resonant frequency, not the natural frequency (where the amplitude isn't at its maximum when there's damping).
Think of it as the good old fashioned "pushing a child on a swing". Their natural frequency will just be what they are oscillating at so if you push everytime they are at maximum amplitude (closest to you) then they will keep gaining energy hense go further and further during each swing. - This is resonance.

Resonant is not a frequency, its just the name given to the situation when the driving force (you pusing the swing) matches the natural frequency of an oscillating object (the child in the swing), hence it gains maximum energy.

I think you may have got some of your definitions muddled up.
15. (Original post by havinghoops)
IDG what's confusing.

Resonant frequency occurs when the driving force matches the natural frequency of the oscillating system.

So for resonance:

driving force = natural frequency

So, this is where there is maximum energy transfer.

And thanks Kameo for answering my question.

abby'sthe best - what units are you looking for? You won't find past papers for unit 5.
I get that <_> But the books talking about when it's damped. On the amplitude/frequency graph you see that the resonant frequency reduces when the system is damped as well as the maximum amplitude. But it says even when it's damped maximum energy transfer STILL happens at the natural frequency - should it not happen at the RESONANT frequency? where the amplitude is maximum?

It's saying when it's damped (the red line), maximum energy transfer happens at f0 (the natural frequency), rather than f1. When it's damped f0 has a lower amplitude than f1, doesn't make much sense to me <_> Shouldn't maximum transfer (when it's damped) be at f1?
16. (Original post by Sasukekun)
Is that diagram straight from the book because I would have thought f0 and f1 one would be in the same place.

Also, one more test paper.
Attached Files
17. madeuptest4.docx (55.3 KB, 370 views)
19. (Original post by havinghoops)
Is that diagram straight from the book because I would have thought f0 and f1 one would be in the same place.

Also, one more test paper.
Yeah, two of my three texts books show that's what happens (the third doesn't have a diagram in the first place ;x)

http://en.wikipedia.org/wiki/File:Resonance.PNG
20. (Original post by Kameo)
when it says define SHM, you say something like

restoring force of an oscillating system is directly proportional to its displacement which is in the opposite direction to the force. ?
best to say.....and it acts towards the mean/equilibrium position
21. (Original post by fredbraty)
People,

Do we need to know what nuclear fussion,fission is?What weak/strong interaction is?

In the hodder book it does not mention anything.
yes we do need to know it. its there in the spec NO 137

i doubt you need to know anything about those intercations
22. (Original post by Sasukekun)
I get that <_> But the books talking about when it's damped. On the amplitude/frequency graph you see that the resonant frequency reduces when the system is damped as well as the maximum amplitude. But it says even when it's damped maximum energy transfer STILL happens at the natural frequency - should it not happen at the RESONANT frequency? where the amplitude is maximum?

It's saying when it's damped (the red line), maximum energy transfer happens at f0 (the natural frequency), rather than f1. When it's damped f0 has a lower amplitude than f1, doesn't make much sense to me <_> Shouldn't maximum transfer (when it's damped) be at f1?
i believe its the hodder book that you are quoting. i too dont understand the energy part.

let me try and google it

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