happen.
1. The length of the spring increases by a far greater
amount for each extra newton of force added.
Hooke's law is no longer obeyed - the line on the
graph curves upwards:
Plan & Prediction:
Apparatus: Stand, Hook, Metre rule, a rubber band, small 30cm ruler. 1 Newton weights x 10
Variables: Control: Amount of weight added in one go.
Independent Variable: Amount of weight added.
Dependant Variable: Length of rubber band or spring.
To make the experiment precise as possible I will get a second judgement every time I record a reading. I plan to keep the experiment a fair test by using the same metre rule and same spring and rubber band.
Prediction: The rubber band does not obey Hooke’s law because the atoms in rubber are all squashed together, so when a rubber band is pulled the molecules start to unfold and therefore making the rubber band longer. The rubber band will stretch the most at the start because the molecules will be easily unfolded. Once all the molecules have been unfolded and are in a straight line the rubber band has reached its elastic limit. If the rubber band is pulled more after it reaches its elastic limit it will be on its plastic limit. The spring will obey Hooke’s law as the molecules in a spring are arranged in a coil order and will stretch an equal length each time a weight is added.
Method:
First put on safety goggles.
Next set-up your apparatus as shown below.
Now start with your rubber band.
First record the measurement at the hanger.
Now add 1N
Then record the result by getting your small ruler and going across from the bottom of the spring to the 1m rule and record the result. Remember to try and keep your small ruler as horizontal as possible.
Now do steps 5-6 again each time adding on 1 extra Newton until your total gets to 10N.
Now re-do the whole experiment again with the rubber band this time.
Obtaining Evidence
Table of results:
Analysing the Evidence
Graph:
As with computerised graphs a best-fit line cannot be created therefore a hand drawn graph will also be available with this experiment.
Conclusion:
After doing this experiment I found out that a rubber band does not obey Hooke’s law which is the same view as my prediction,
” The rubber band does not obey Hooke’s law because the atoms in rubber are all squashed together, so when a rubber band is pulled the molecules start to unfold and therefore making the rubber band longer. The rubber band will stretch the most at the start because the molecules will be easily unfolded….”
I have accepted my prediction as it was right and did state that a rubber band will not obey Hooke’s law and I was right as it didn’t so I accept my prediction.
Also my scientific knowledge proved that a rubber band would not obey Hooke’s law as it stated that rubber was an ‘exception’
Evaluation
Evaluation:
My conclusion is the same as my prediction and also my scientific knowledge stated that a rubber band would not obey Hooke’s law
In my investigation I did the following to make sure my experiment was a fair test:
- I made sure that I kept the same rubber band.
- I made sure I added an equal number of weights each time.
- I made sure I double-checked my readings.
- I made sure that there were no movement of the apparatus while I was conducting the experiment.
- I made sure that I waited for the rubber band to stop moving after adding each weight.
I took one set of readings for my results. I could have improved my work by doing the following:
- I could have taken two sets of readings to increase the accuracy in my results, and reduce the chances of an anomaly.
- I could have taken three sets of readings to make sure my results were very precise nd accurate.
- I could have compared a spring with a rubber band and talk about there differences and similarities.
After looking at my computerised and hand drawn graph I found that there were not any results that did not fall on my best fit curve, the reasons for this may have been that I was very accurate in my readings and that they were very precise.
If I did this experiment again I would make the following changes:
- I would take the results down three times to improve the accuracy and precision of my results.
- I would do the experiment with more weights so that we could see at what weight would reach the rubber bands elastic limit.
I could have improved my results and readings if I had done the following more carefully:
- By double-checking the readings.
- Taking care not to move the apparatus while conducting the experiment.
I can also do this investigation in a number of different ways:
- Conduct the experiment with different types of rubber bands so that I could compare the differences and similarities between them.
- I could conduct the experiment with a spring as well as a rubber band so that I could compare them.
