water and air

week three of grade eight physics




Physics for grade eight included four days spent on the properties of water and air. This week allowed for some exciting movement games with water and balloons! For instance, we played a game called life raft, a relay race where two teammates held a balloon between their backs in order to get the teammate across to the other side.

Liquids and gases are both fluids, and share similar properties. Volume, mass, and density were measurements we took of liquids such as glycerin, water, vegetable oil, and alcohol, and air.

I described what volume is, the space that is occupied by fluid and taking on the shape of the vessel. We measured 200 mL each of the liquids, then weighed and compared them. We then calculated for density (D=M/V). Once we had our figures, we predicted the outcome of putting all the liquids together in a tall beaker. I used food coloring mixed with glycerin and with the alcohol. Pouring each one carefully into the beaker containing water, the glycerin flowed to the bottom, the oil rested atop the water, and the alcohol rested on top of the oil. This demonstrated the different densities of each.

We also calculated for air. I filled a balloon with air and submerged it into an aquarium, marking the level of water before and after. We calculated for volume by measuring the height change multiplied by length and width of the aquarium (V=l x w x h). Then we measured the balloon filled with air on a scale, and again after I popped the balloon, and we got the weight of air in the balloon. By calculating D=M/V, we arrived at an answer. Unfortunately, our calculated result did not match the expected density (0.00013 g/mL)! I think there was too much moisture in the air I blew into the balloon (moisture reduces the density of air). It was a good lesson in learning how scientists need to be able to postulate and record where errors may occur in experimentation!

Additionally, the non-compressible properties of fluids allowed us to discuss the work of fluids, as with hydraulics and pneumatics. A typical piston assembly allows us to apply force in one area and transmit it as force exerted in another area.