The Density of Wood Blocks is an excellent, middle school activity. I got the idea from the NSTA publication "Science & Children" about 12 years ago. The activity involves many skills, all of which are part of our 6th grade science curriculum.
Each class is divided into 4 groups and each group is given a set of 6 wood blocks of different sizes. One group has set A, one group has set B, one set C, and one set D. The wood types are oak, ash, pine, and poplar. First, they have to determine the mass of the blocks using a pan balance scale.
Then the kids have to measure the length, width, and height of the blocks to the nearest mm. Using the formula V= L x W x H, they figure out the volume of their blocks. All this data is recorded on their data chart.
Next, they figure out the density of their wood blocks by using the formula D = M / V. They do this using calculators and rounding off to the nearest 0.01 g/cm3. They then find the mean (average) density of their 6 blocks.
Then, using the document camera, the 4 groups share their data with the other groups so that when done, all four groups have all four sets of data.
What really makes this activity come to life is that the then kids graph the density of all 4 woods. They make a volume / mass graph and plot the 6 sets of data points for each block, creating a line graph for each wood. They color code each line and make a key. When done, they have a good, visual picture of the different densities.