Expert: Paul Klarreich - 1/29/2006

Question
My proffesor gave me a paper to do consisting of uestions like a baseball is about _ cm. in diameter and a dime is about _mm thick. How am I suppose to know These things or how do I find out how to do it? Also we are learning about how to measure density, d=mass/volume. I am having trouble with this process.

Answer
Hi, Kerrie,

Your Question:  My professor gave me a paper to do consisting of questions like a baseball is about _ cm. in diameter and a dime is about _mm thick. How am I suppose to know These things or how do I find out how to do it? Also we are learning about how to measure density, d=mass/volume. I am having trouble with this process.
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This is not strictly about mathematics, I must say, but about:

1. How am I supposed to know these things?  I suppose you could look in some encyclopedia of baseball or of currency.

2. About determining mass and volume:  You determine the mass of an object by weighing it on a metric scale or, if you don't have one, convert your pounds to grams using the proper conversion factor (which you look up somewhere).

You determine the volume of an object by this process:

A. Fill a vessel with water up to the very, very top.  Do this in the sink so your mommy will not get very, very angry.

B. Put the object into the vessel.  Make sure it sinks.  Push it down if you have to.  Some water spills out.  

C. Remove the object, making sure that any water on it drips back in.  

D. Carefully measure the water necessary to refill the vessel to the very, very top.  Express this in cubic centimeters.  (Use a metric-labeled measuring cup.)

Finally, density is mass(in grams) divided by volume(in cubic centimeters.)

If your object sank without you having to push it down, your density should be more than 1.0, but if your object floated and you had to push it down, the density will be less than 1.0

Does that help?