Physics coursework help needed!

Am doing a2 Physics coursework on damped oscillations

Here is my introduction, but i have no idea what to do on background theory can anyone help?

Introduction
In my experiment I will be investigating the exponential decrease in the amplitude of oscillations using a simple laboratory arrangement. I will vary the air resistance on the mass, using different size cards. I will also vary the time to see what affect these have on the amplitude of the oscillation. I will keep the mass constant while changing the sizes of the card, and measuring the amplitude of the oscillation for different times. The mass will be 20g and the amplitude of the oscillation will be measured using a ruler. I will do this for five different size cards in increments of 1cm², starting with a card of 2 cm² and finishing at 7cm² and six different times starting at 5 oscillations and finishing at 30 oscillations. When I have sufficient results I will plot graphs of amplitude against time, which will show the characteristic exponential decrease. Then I will find the ‘half-life’ of the graphs by determining the time it takes to decrease to half its initial value. By changing the size of the graph it is possible for me to change the degree of damping and hence alter the half-life.

Reply 1

davey_boy

9

MOWLID

Am doing a2 Physics coursework on damped oscillations

Here is my introduction, but i have no idea what to do on background theory can anyone help?

Introduction
In my experiment I will be investigating the exponential decrease in the amplitude of oscillations using a simple laboratory arrangement. I will vary the air resistance on the mass, using different size cards. I will also vary the time to see what affect these have on the amplitude of the oscillation. I will keep the mass constant while changing the sizes of the card, and measuring the amplitude of the oscillation for different times. The mass will be 20g and the amplitude of the oscillation will be measured using a ruler. I will do this for five different size cards in increments of 1cm², starting with a card of 2 cm² and finishing at 7cm² and six different times starting at 5 oscillations and finishing at 30 oscillations. When I have sufficient results I will plot graphs of amplitude against time, which will show the characteristic exponential decrease. Then I will find the ‘half-life’ of the graphs by determining the time it takes to decrease to half its initial value. By changing the size of the graph it is possible for me to change the degree of damping and hence alter the half-life.

1: How do you know the decrease in amplitude will be exponential? If you know this then you need to say how - e.g. it has been observed in a series of experiments (such as...) that the amplitude of damped oscillators decreases in an exponential fashion. If you don't know then don't use the word - and if this is the case, you'll need to remove your section on measuring half-life.
2: You don't say what your 'simple laboratory arrangement is'. I assume you're using a spring with a mass attached - you need to mention this.
3: Don't know what you mean by "I will also vary the time to see what affect these have on the amplitude of the oscillation." - you need to explain that better.
4: I seem to remember errors being quite important when I did A-levels, you might want to mention reduction of errors somewhere (e.g. repeating readings).
5: As for background theory, if you know enough maths, you could talk about the maths of the situation, md2x/dt2=-kx-cdx/dt or whatever it is....

Hope this helps.

Reply 2

thatsthebadger

iam doing this for as ocr advancing physics, except we only have to analysie and evaluate the results, and explain harmonic motion, not collect them like u.

its quite hard, but i might be able to help.

got any good resources on how simple harmoic motion works?

Reply 3

davey_boy

9

thatsthebadger

iam doing this for as ocr advancing physics, except we only have to analysie and evaluate the results, and explain harmonic motion, not collect them like u.

its quite hard, but i might be able to help.

got any good resources on how simple harmoic motion works?

What do you mean 'how it works'? - A google search for simple harmonic motion throws up several sites with basic desriptions....

Reply 4

MOWLID

OP

I think you guys have misunderstood what i am doing i will try and explain it better.

I can investigate the exponential decrease in the amplitude of oscillation using a simple laboratry arrangement. A hacksaw blade is clamped vetically to a clamp stand. A mass is attached to the free end. this will oscillate freely if you displace it to one side.

A card is attached to the mass so that there is a lot of air resistance as the mass oscillate. Thea mplitude of the oscillations decreases and can be measured every five oscillations by judging the position of the blade against a ruler fixed alongside. A graph of amplitude against time will show the characteristic exponential decrease. You can find the half-life of this graph by determining the time takes to half its initial value. By changing the size of thecard it is possible to change the degree of damping and hence alter the half life of the graph

please help thanxs

Reply 5

davey_boy

9

MOWLID

I think you guys have misunderstood what i am doing i will try and explain it better.

I can investigate the exponential decrease in the amplitude of oscillation using a simple laboratry arrangement. A hacksaw blade is clamped vetically to a clamp stand. A mass is attached to the free end. this will oscillate freely if you displace it to one side.

A card is attached to the mass so that there is a lot of air resistance as the mass oscillate. Thea mplitude of the oscillations decreases and can be measured every five oscillations by judging the position of the blade against a ruler fixed alongside. A graph of amplitude against time will show the characteristic exponential decrease. You can find the half-life of this graph by determining the time takes to half its initial value. By changing the size of thecard it is possible to change the degree of damping and hence alter the half life of the graph

please help thanxs

That sounds a lot better to me - you've actually explained what you're doing.

You can see from the fact that I was thinking about a completely different experiment that your original explanation was too vague. Personally I'd just re-write your final paragraph to make it sound more formal and incorporate it into your initial attempt and I think you've got the basis of a good introduction.

Reply 6

MOWLID

OP

thanks for your help so far, but do you think yo can help me on background theory(can't find anything on google) and errors& analysis.

thanks

Reply 7

elpaw

15

have a look at page 30-onwards of http://www.physics.ox.ac.uk/users/ross/complexcomplete.pdf

Reply 8

davey_boy

9

MOWLID

thanks for your help so far, but do you think yo can help me on background theory(can't find anything on google) and errors& analysis.

thanks

http://hyperphysics.phy-astr.gsu.edu/hbase/shm.html
gives some stuff on Simple Harmonic motion.

http://www.batesville.k12.in.us/Physics/PhyNet/Mechanics/Newton2/air_resistance.htm
gives some stuff on Air resistance (navigate through other useful chapters using arrows at top of page).

Put it together and you've got the background for your experiment.

Errors I'm not too hot on - there are so many definitions that I don't want to tell you the wrong one. You need to consider what errors there are in the system - what are you going to do? e.g. time of oscilation - how is it measured? What are you using to measure it? How accurate is this device? What human errors might be introduced (like pressing the stopwatch button at slightly the wrong time)?

Physics coursework help needed!

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