# Density Lecture

When you ask someone which is heavier, a rock or a feather, most people will say it’s the rock. But in truth, that’s not always the case. What if you compared a tiny pebble to a whole truckload of feathers? What people really mean, when they say, “rocks are heavier,”  is that rock has a higher density.

Today in class, students listened to a lecture about the concept of density. It’s an important one; a boat’s density is the difference between a peaceful cruise and a shipwreck disaster. We can calculate an object’s density using the formula d = m/v. This is the same principle that guides the flight of hot air balloons, keeps icebergs afloat, and makes oil spills practical to cleanup (if all the oil sank, we’d be in big trouble!)

Afterwards, students used the density formula to calculate the density of vegetable oil, rubbing alcohol, maple syrup, water, and salt water. When mixed together, the liquids actually separate into predictable layers based on their densities. The higher densities sink to the bottle while the lower densities float to the top.

Tonight’s HW is the Checkpoint Quiz which can be accessed by clicking on the previous link. Just type in your name and answer the ten questions to see how you are doing so far in Unit 1.

September 14 – Density Notes (pg108)