Catapult Investigation - page 2
Keywords: Physics elastic spring stretch
By Jenny on 02/07/2009
Level: GCSE Key Stage 4 (Years 10-11)
Page Number: 2 of 3 pages: 1 2 3
that it’s facing directly along the measuring tape).
6. Pull back the elastic 0cm using the ruler to measure it.
7. Release the elastic.
8. Observe how far along the tape measure the pellet landed.
9. Record it in the results table.
10. Do this twice more with the elastic pulled back the same amount.
11. Finally, repeat the whole thing with the elastic pulled back 2cm, 4cm, 6cm, 8cm and 10cm (do the experiment three times for each length to ensure you get an accurate result).
Results Table
Distance propelled (cm)
Distance pulled back (cm) 1 2 3 Average (1+2+3)/3
0 0 0 0 0
2 301 219 260 263
4 307 320 216 281
6 340 373 324 346
8 452 478 444 458
10 537 591 427 518
Analysis
My graph at first climbs upwards very steeply then continues to rise more steadily. This is because when the elastic wasn’t pulled back at all (0cm) there was no strain energy and therefore no kinetic energy and the pellet went nowhere. After this the experiment went pretty much as I predicted, the two amounts (how far the elastic was pulled back and how far the pellet went) increasing together in fairly direct proportion to each other. This happened because the elastic contained strain energy when it was stretched and then when it was released this was converted into kinetic energy which propelled the paper pellet. The further back the elastic was pulled the more strain energy there was and so more kinetic energy was produced which propelled the pellet further. The curve isn’t as smooth as I expected it to be and there is also a wide variation in some of the results for the same length – as much as 164cm.
Evaluation
I think that my experiment was fairly accurate as I repeated it three times at each length. However, there is quite a large amount of variation between different results for the same length. The biggest is between the results for 10cm: pellet 2 went 591cm while pellet 3 went only 427 - a difference of 164cm! Also a few of the results were a little bit off, for example the result for 4cm was lower than I would have predicted and the curve of the graph isn’t as smooth as I was expecting. This was probably caused by human error. To minimise this and get more accurate results I could have done some test shots beforehand to check that the long flat surface was big enough. Also I could have done more different lengths and repeated each length more times to ensure that I got an accurate result. If I did this experiment again and I had
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