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# Hooke's Law watch

1. I was doing an expirement today in class and we were looking at Hooke's Law, and the equation F=ke or F=kx... Whilst doing the expirement we were to told to explain any problems/limitations whilst doing the experiment so reading off the value of the extension and the spring moving etc... can anybody else think of any other problems whilst performing the experiment?Thanks.
2. Without knowing your exact experimental procedure it's difficult to say.

You should look at common sources of error, and see how they apply to your experiment.

Human error is a common example, and you've identified this when you said "reading off the value of the extension".

Other common sources of error:

Parallax - when taking a measurement where there is any distance between what's being measured and the scale being used, then if your eye is not in exactly the right place, the measurement you read can be distorted either way.

Resolution - All measuring instruments have a minimum unit to which they can measure to. E.g. a ruler might measure to the nearest 1 milimetre. This introduces an uncertainty in the measurement because your measurement could be anywhere between +/- 0.5 of the minimum unit. For example, say you measured the diameter of a ball to be 17mm, and your ruler only measured to the nearest mm, the actual diameter could be anywhere between 16.5 and 17.5mm, and you would still record it as 17mm, so it would have an uncertainty of +/-0.5mm. - This can occur with multiple measurements within the same experiment, not just with length measurements.

Other factors - think carefully about the assumptions you've made regarding your setup, and how these might not be perfect - these will be very specific to your setup, and the components you've used.
3. (Original post by james153)
Without knowing your exact experimental procedure it's difficult to say.

You should look at common sources of error, and see how they apply to your experiment.

Human error is a common example, and you've identified this when you said "reading off the value of the extension".

Other common sources of error:

Parallax - when taking a measurement where there is any distance between what's being measured and the scale being used, then if your eye is not in exactly the right place, the measurement you read can be distorted either way.

Resolution - All measuring instruments have a minimum unit to which they can measure to. E.g. a ruler might measure to the nearest 1 milimetre. This introduces an uncertainty in the measurement because your measurement could be anywhere between +/- 0.5 of the minimum unit. For example, say you measured the diameter of a ball to be 17mm, and your ruler only measured to the nearest mm, the actual diameter could be anywhere between 16.5 and 17.5mm, and you would still record it as 17mm, so it would have an uncertainty of +/-0.5mm. - This can occur with multiple measurements within the same experiment, not just with length measurements.

Other factors - think carefully about the assumptions you've made regarding your setup, and how these might not be perfect - these will be very specific to your setup, and the components you've used.
Right, thanks a lot! Gave me a few ideas to expand on.
4. Take care you're measuring from the same spot of the spring each time when measuring the extension.

if it's the experiment where you add the weights then maybe use 50g standard masses instead of 100, more results means less .. I forget the word... Reliability?

you can add a pointer or something to the ruler to make the parallax effect less apparent.

All I can quickly think of at the top of my head.
5. (Original post by ChillGod)
Take care you're measuring from the same spot of the spring each time when measuring the extension.

if it's the experiment where you add the weights then maybe use 50g standard masses instead of 100, more results means less .. I forget the word... Reliability?

you can add a pointer or something to the ruler to make the parallax effect less apparent.

All I can quickly think of at the top of my head.
Yes the 'pointer' is a great method to reduce parallax error... and would reduce the percentage uncertainties within the experiment.

Thanks.

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