Ame E. Posted October 31, 2008 Share Posted October 31, 2008 This was experiment 4.5 in module 4 of Exploring creation with physical science, using the first edition of the book. We cut parallel pieces of thread... held the threads about an inch apart and then gently placed a sewing needle on top of the threads and lowered the threads with the needle into a bowl of water... Actually just so that the threads touched the surface of the bowl or water.. The bowl was full but not overflowing.. We used a soup bowl with a rim... then we let go of the threads and the needle was supposed to stay floating on the water... As soon as we let go of the threads, the needle sank... We added dishwashing soap, and the needle stay sunk... It was supposed to be that the needle would float because of surface tension.... adding dishwashing liquid was supposed to cause the needle to sink... thanks Ame E. Quote Link to comment Share on other sites More sharing options...
Ame E. Posted October 31, 2008 Author Share Posted October 31, 2008 it worked this time... the paper clip did not sink.. interesting... wonder why the paper clip worked and the needle didn't. ame Quote Link to comment Share on other sites More sharing options...
GailV Posted October 31, 2008 Share Posted October 31, 2008 Maybe you broke the surface tension with the point of the needle without realizing it? The paperclip has a more round shape. Also, it's flatter/wider. Quote Link to comment Share on other sites More sharing options...
Sharon in MD Posted October 31, 2008 Share Posted October 31, 2008 If the needle and threads happen to have any thing on them it can interfere with the surface tension as well. It can be tricky to get it just right. Quote Link to comment Share on other sites More sharing options...
Rhondabee Posted October 31, 2008 Share Posted October 31, 2008 Try it by placing the needle on a tissue paper "boat". The tissue paper will sink, leaving the needle floating on the water. It took us about 5 times to do it right with the strings. The next year, my younger ds did the tissue paper version, and we did it over and over, because it worked every time. (That so rarely happens around here, we revel in it when it does!) hth, Rhonda Quote Link to comment Share on other sites More sharing options...
PamJH Posted November 1, 2008 Share Posted November 1, 2008 This is why scientists conduct the same experiment multiple times. They want to rule out changes in variables and to see if lightning strikes twice, so to speak. This will be good for us to remember this year at our house. If the experiment doesn't work the first time, try again. Thanks for posting. Quote Link to comment Share on other sites More sharing options...
TRILLIUM Posted November 2, 2008 Share Posted November 2, 2008 Remember experiments never fail. Demonstrations fail. Although experiments give unexpectected results they can't really fail. What happens in the experiment happens. Experiments can be poorly designed, when this happens it is hard to draw conclusions from results. A "failed experiment" actually can allow you to explore. When you lower an object onto the water the force of gravity acts on the object in the downward direction. In order to sink it will be necessary to "break the surface tension" A sciency thing to do would be to pick up pack of needs and see if some float and other don't. You would see that it would depend on the surface to volume ratio. For a needle of constant diameter surface is 2*pi*r*l. The volume, which is a (measure of mass given constant density) is pi*r^2*l. So surface varies proportionaly with r and volume (and thus mass) with r square. What you should find is that while very thin needles float there will be a radius where they begin to sink. Of course this is looking at a simplified geometry the eye shape of the needle would also effect you results if you were close to equilibrium. Quote Link to comment Share on other sites More sharing options...
Ame E. Posted November 2, 2008 Author Share Posted November 2, 2008 I am going to have my children read them as well! Ame E. Quote Link to comment Share on other sites More sharing options...
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