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Friday, May 1, 2015

More investigations with sound

Today we tried a few more sound investigations.
We know that big objects make low sounds while small objects make high sounds.
First of all we lined up spoons according to size.
Then we tried listening to them.  To do this we tied string around the spoons, then put the string up to the outside of our ears.
The sound of the spoon banging against something hard (like the leg of a chair) caused the vibrations to go through the spoon and into our ears.
Sure enough the small spoon make the sound of a high bell, while the large ladle made the sound of a very low church bell.
Teacher was wondering what happens when you drop a small stone into water.
We explained that the stone causes the water to vibrate and that we can see this as circular waves in the water.  We wondered if this happens only in circular containers, but some of us have noticed this in the sea and that's not a circular container, so we think it happens no matter where you drop the stone in water.

Teacher had a tuning fork in class.
She showed us how to use it, and how to get it to sing a note by causing the prongs to vibrate and then holding the other end to the table or to the bone under our ears.  We loved this.
We wondered what would happen if we put the vibrating tuning fork into water.
Boy did we get a surprise! (The vibrations caused the water to ripple in circles, the circles bumped into each other and the water droplets came jumping out of the container.
Next we tried pressing a vibrating tuning fork against a container of rice and a container of peas. 
It was fun to hear the buzz and see the rice and peas jump.
You should also try this with a ping pong ball on a string.  This really is fun.
When you touch the vibrating tuning fork off the ball the vibrations of the tuning fork cause the air inside the ball to vibrate, which in turn make the vibrations stronger which then makes the ball bounce around.
Next we spotted some string telephones.
These work when the sound waves travel through the (tight) string and into the cup.  The cup then amplifies (makes louder) the sound of our voices.
It was quite hard to keep the string tight and to make sure we didn't touch the string with our fingers or the sides of the cup.  These telephones are great for telling secrets!
We really are experts on sound and vibrations now!

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