Carlos,

1g = 1 ml for pure water at 4 C. That's because the density is 1.000 g/ml. Different substances have different densities. For example, wood is less dense than water (that's why it floats: lower density
substances float on higher density fluids). Canadian maple is about 0.750 g/ml, balsa is 0.170 g/ml and pine is about halfway between them.

A hollow (but enclosed) irregular wooden shape such as a closed tube or a ball would be less dense as an enclosed object, since it has a large volume (it includes the air pocket inside), but the mass is about the same as just the wood part. Since density is mass over volume, if you increase the denominator and keep the numerator the same, you have a smaller fraction. Of course, the wood portion itself doesn't change density - it's just that the whole object has a lower density than one without an air pocket.

I'm not sure about what you mean about partially submerging the block though.

Stephen La Rocque.>

Carlos,

When I read part b I assumed that your son was to imagine an experiment to determine the density of an irregular shaped wooden block. To do this you weigh the block to find its mass and then measure the volume. One way to measure the volume is to fill a container with liquid, submerge the block and measure the volume of liquid that overflows the container. The volume of liquid displaced by the block is equal to the volume of the block. If you don't completely submerse the block then the volume of liquid that overflows will be less than the volume of the block.

Penny