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Busy day in grade 9

March 18, 2019

Today we developed the formula for calculating the volume of a sphere using a tennis ball and a juice container, some water and a displacement tank.

The important thing to know is that a juice container has the same radius as a tennis ball.  We cut the container so that it is the same height as the tennis ball too.  The height of the cylinder is the same as the diameter of the cylinder, or 2r.

We fill the displacement tank and let it drip until the water is just at the level of the spout.


When the water stops flowing from the spout, we place the empty juice can under the spout and then we submerge the tennis ball, and press it down under the water.  The water displaced by the tennis ball will flow into the juice container.


The water stops flowing, and the container is 2/3 full.

Here comes the math:  the volume of the cylinder is V=(pi)(r)^2(h), but remember h=2r since we cut it.

V=(pi)(r)^2(2r)

V=(pi)(r)(r)(2)(r)

V=2(pi)(r)^3

Now we know that the sphere’s volume fills 2/3 of the cylinder

Vsphere=(2/3)(2)(pi)(r)^3   And we multiply the (2/3) and the (2)

Vsphere=(4/3)(pi)(r)^3


We also started an experiment today!  We are going to see if beans will germinate.  We have several kidney beans and black eyed peas, and have put them in paper towel and in a baggie.  We will check in at the end of the week and see the percentage that germinated.


We also looked at bumping up our portfolio writing.  We have submitted one task already, but have a chance to make it better using the feedback we received.

We looked at some composition samples, and highlighted all evidence in yellow, all reflections in green, and all summaries in orange.  We looked at our rubric, and determined where we could add more supporting details, and improve the writing.

We have another composition to do next week, and we’re feeling more prepared!

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