What you need
A glass bottle
Food colour
Modelling day Drinking straw
A small op
A sketch pen
What to do:
1. Plug the mouth of the glass bottle with the modelling day
2. Insert the straws into the clay and then pull it out leaving a straw sized hole in the clay. Make sure you clear out the clay caught in the straw.
3. In the cup, mix a little water with a few drops of food colouring.
4. Dip the straw into the water. Then dose the top end with your thumb so that a drop of water enters the straw
5. Make the straw horizontal and release your thumb, letting the water drop ride back towards your hand when it is somewhere in the centre of the straw re-plug the top with your thumb.
6. Keep the plug with your thumb constant as you push the straw through the hole in the modelling day. Squeeze the day until you have a seal around the straw. Then release your thumb.
7. Place the bottle on a stable surface. Mark the initial position of the drop on the straw with a sketch pen.
8. Now, hold the bottle in both hands while it rests on the table. Observe the drop.
9. Let go of the bottle and let it stand on the table.
What happens :
When you hold the bottle, you see the water drop slowly crawl up the straw. When the bottle is left on its own, the water drop Moves down again. Why?
The bottle is full of air. In fact that is why the drop does not simply slide down the straw when you plug it into the clay seal. The air holds the drop up in the straw.
When you hold the bottle, your body heat warms it up. This causes the air inside the bottle to warm up as well. And warmer air expands. This causes the water drop to move up as the expanding air looks for a way out.
When you let go of the bottle, it cools down gradually. The cooling air contracts and the water drop down again.
You can try this experiment by putting the glass bottle in a hot water basin and then a cold water basin, you want to see drastic changes in the position of the water droplet.
Picture Credit : Google
