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How to make a catapult with only lolly sticks and elastic bands!

January 25, 2018

This is a simple but effective design that I used at Science Crazy last week. 


All you will need is:


  • 9 big lolly sticks

  • 6 elastic bands

  • A pompom, ball of cotton wool a marshmallow or a scrunched up piece of paper  






To assemble…




Stack 7 of the lolly sticks.




Hold them together with 2 elastic bands either end…






Put the other two, one over and one under, across the stack of lolly sticks.  When you do this ensure that one end is shorter than the other and tie an elastic band round the last two lolly sticks at the shorter end, like so…






I add an extra, the last elastic band, to the other end on the top lolly stick like this, to act as a ledge...




NOW YOU ARE READY TO PLAY!  I mean experiment!




First try launching different items.  Which go further? 


You can also try changing how many lolly sticks you use in the beginning stack  (STEP ONE).




Wood has elastic properties. 


When you jump up to grab a low branch in a tree and hold it down, it bends.  What happens when you let go?


In the words of one our young scienctists at Science Crazy Club: ‘It pings up!’


This is true; it's because of the elastic properties in the wood.


One thing the elastic properties can be useful for is producing mechanical energy.  This is how it works.


An outside force, in this case you, pulls on the branch of the tree.


The branch then increases in potential energy, in this case potential mechanical energy, or potential elastic energy as it is sometimes known. 


Potential energy is stored in the branch once bent, and is waiting to be released and transferred into movement -kinetic energy!


Sometimes potential energy is known as stored energy.


When you let go of the branch this potential energy will be transferred into kinetic energy. 


Kinetic means movement, in this case the ‘ping!’  The mechanical energy!


When you use your catapult hold the front down as well as pressing down on the lever, the top in the same way a branch bends the lolly bends because, again, it is wood.  Potential energy stores up the more potential energy stores up waiting to be released.


When you release the lever, after loading it with something light, like a screwed up piece of paper, the energy transfers from potential energy into kinetic energy, in this case mechanical energy, or elastic energy as it also known.




The effect of this is that it creates a push force that the load, your scrunched up piece of paper, pompom or whatever else you chose, on the catapult is propelled in the air.





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