Forces experiments: Air

We did some very interesting experiments today.

They were all about air.

 Teacher had two identical 2l coke bottles.  Each had an identical yellow balloon inside.

She gave us the bottles to blow up the balloons.

No one was able to blow the balloon in the first bottle.

We had lots of guesses as to why this might be so.

We found out later on that the reason we couldn't fill the balloon is because the bottle was already full of air.
It was easy to blow up the balloon in the other bottle because teacher had put little holes in the bottle for the air already in the bottle to escape. Now we know that "empty" bottles are not really empty at all.  They are full of air!

We squeezed the air out of a bottle and then put on the lid.  It was impossible for the bottle to go back into its original shape until we let the air back in!

Next we tried to blow a ball made of tissue into a bottle.  We tried blowing really hard but none of us could manage to score the goal.

Finally we were able to do this when we used a straw and blew all our air directly at the ball.

When we just blow without the straw, the air from our mouths goes round the ball, bounces off the back of the bottle and then comes back out again, taking the tissue ball with it.  We are definitely going to try this one at home.

Have you ever had a conversation with a bottle?

You should try this:  Fill a bottle with really cold water and then empty out the water.  The air in the bottle is now very cold.  Wet the lid and put it upside down on the bottle.  Now warm the air in the bottle with your hands.  The air in the bottle warms up and because it takes more space than cold air, the warm air pushes out from under the lid.  As you keep warming the air, the lid keeps popping up and down, and looks like it is talking to you.

Now for something impossible!

If you try to blow a ping pong ball up out of a funnel you will find that it it an extremely tricky thing to do.

In fact it can't be done.  The air from your lungs sticks to the side of the funnel and won't have enough force to push the ball out of the funnel (even if you use a straw....we tried  this so we know!)

In fact, it is almost impossible to blow a candle out if you blow through a funnel.

Only Ms. Lally could manage this one!  We think maybe she had the rim of the funnel near the flame, but maybe she is just exceptionally talented!

Now for the serious fun:

We made our own sprays! With just a straw cut in two and a glass of water, we were able to spray water droplets.

The straw standing in water is filled with water and air.  As we blow the air from around the top of the straw in the water, we create an area of low pressure.  The air in the straw rushes to take the place of the air blown away.  As we continue to blow, the water in the straw rushes to take the place of the air blown away.  As the water reaches the top we blow that too and separate the little water droplets which come squirting out in a fine spray.

All these experiments are fun (and safe) to try at home.

We will show you how if you like 'cause we are great scientists!