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

1. Can Someone explain me S.H.M please, I dnt seem to understand it.
2. (Original post by Pegasus92)
Can Someone explain me S.H.M please, I dnt seem to understand it.
The whole topic?
The whole topic?
I dnt understand the topic from the start, so Im stuck, just explain the start bit,
4. Definition of SHM: When an object is displaced from the midpoint, in a motion that means the acceleration is proportional to the displacement in the opposite direction.

So, imagine a pendulum. The middle, where it hangs naturally is the midpoint. Now it's swinging from left to right. When it swings to the left, there is a restoring force towards the midpoint, so to the right, or it would never go back to the midpoint, would it? This acceleration is proportional to the amount of displacement from that midpoint.

So, that's the very beginning. What else are you having problems with? Formulas?
5. (Original post by havinghoops)
Definition of SHM: When an object is displaced from the midpoint, in a motion that means the acceleration is proportional to the displacement in the opposite direction.

So, imagine a pendulum. The middle, where it hangs naturally is the midpoint. Now it's swinging from left to right. When it swings to the left, there is a restoring force towards the midpoint, so to the right, or it would never go back to the midpoint, would it? This acceleration is proportional to the amount of displacement from that midpoint.

So, that's the very beginning. What else are you having problems with? Formulas?
thanks
Im revising S.H.M
Ill ask whenever I get doubts on any sections.
6. It relates very well to circular motion and waves, so if you're finding it difficult, it would be a good idea to have a quick revision of these topics as well.
7. (Original post by havinghoops)
It relates very well to circular motion and waves, so if you're finding it difficult, it would be a good idea to have a quick revision of these topics as well.
the equations of displacement with time, I dont seem to understand it!
can you expalin/
8. The ones with cos and all that?
9. (Original post by havinghoops)
The ones with cos and all that?
yeah
10. (Original post by Pegasus92)
the equations of displacement with time, I dont seem to understand it!
can you expalin
You should have visited Mr Oliver's Lecture yesterday.
It was all about SHM. And a bit of meerkats.
What dont you understand in the equations?
11. (Original post by Pegasus92)
Can Someone explain me S.H.M please, I dnt seem to understand it.
http://www.s-cool.co.uk/alevel/physi...ic-motion.html
12. I'm going to explain this the only way I know how.

I have used a diagram of a circle, even though it is NOT circular motion. They're related, so to explain I have used it, as it is the only way I can visualize it.

The equation is x = A cos (wt)

So, the part I have marked 'x' is the displacement. You would work this out doing cos (theta) multiplied by the hypotenuse of the triangle (because its a component of it).

You know from circular motion that w (angular velocity) = theta / time.

So, rearranging, you get theta = wt. So you would then get cos (theta) = cos (wt).

You would then multiply it by A, as that is the hypotenuse of the triangle (which I haven't marked in the diagram, whoops)!

I do not know if you do A-level maths, but all the other equations are basically differentiated from x = Acos(wt).

So, dx / dt = velocity. In words, the rate of change of displacement is velocity. Differentiating A cos (wt) = -Awsin(wt).

So you get velocity = -Aw sin (wt)

dv / dt = acceleration. In words, the rate of change of velocity is the acceleration. You already know this, it's just put in mathematical terms. Differentiating -Awsin(wt) = -Aw^2 cos(wt).

Don't worry if you don't know how to differentiate the equations, you don't need to. They're given to you. Just now you know where they come from.

The points marked P on the diagram are just the particle moving from one point to another. A is the max amplitude.

Hope this helps.
Attached Images

13. (Original post by havinghoops)
Thanks to whoever uploaded all those hundreds of questions on all the topics ! They've been really useful.

I've been putting them together in a way that means the marks add up to 80, so I sit it like a mock test and get some kind of idea of what I might realistically get. They're just random questions picked out of those documents, so they add up to 80 marks.

I'll share the rest of them tomorrow if people want more. At school so only have one of them atm.
Thank you soo much for this
Really appreciate it
Can you post the other too
+rep
14. Yup no problem, I will PM you when I have uploaded the others.
15. Anyone done the specimen paper?

What in the hell is question 10 asking for? I swear its not even gramatically correct.

Here's the question:

16. (Original post by BPat)
Anyone done the specimen paper?

What in the hell is question 10 asking for? I swear its not even gramatically correct.

Here's the question:

I suppose 'with time' is the end of the sentence.
Even the mark scheme is wrong.
17. (Original post by havinghoops)
Yup no problem, I will PM you when I have uploaded the others.
where have you uploaded the first one?
18. What about that multi-choice question where it's oscillating back and forwards through time? Had a good giggle at that one

Pegasus92, page 12 At the end.
19. (Original post by havinghoops)
The ones with cos and all that?
thanks a lot, seem to understand it now.
20. No problem If you need help with anything else, just let me know I find it helps me understand things better too if I have to explain it.

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