Pencaitland Primary Blog

Lesson 11 - 24/01/07

Following on from where we left off yesterday, we finished our divers by adding a small amount of blu-tack to their feet, so that they just floated in a bucket of water.  If we added too much they sank to the bottom.

Then came the fun part! We filled up 2 litre drinks bottles with water and put our diver in.  We screwed on the cap and found that the diver floated at the top of the bottle.  We were amazed that when we squeezed the bottle the diver sank to the bottom and when we let go, he swam back to the top. Incredible - but why?

In groups we talked about why we thought this had happened, then we all got together to pool our ideas.  We decided that when we squeezed the bottle it pushed water into the straw (which was our air tank), squeezing the air into a smaller space .  This makes the diver denser and so he sinks. When we let go of the bottle, the squashed air pushes the water back out of the straw, so the divers density decreases and he floats back up to the top.

I thought it was fun when you squeezed the bottle and the diver went down.   Robert P

Our man had too much blue tac on his feet and he sank to the bottom    Johnny

I liked putting on the blue-tac and trying to get him too just float in the bucket     Mark

I liked filling up the bottle    
Erin

Me and Rachel had to squeeze the bottle together to make the man sink        Nicole

I liked putting the man into the bottle and guessing if he would float      Lois

I liked squeezing the bottle to try and get him to sink to the bottom but I couldn’t     Alistair