1/13/11

Post date: Jan 13, 2011 2:7:57 PM

• • Bell ringer: Does the shape of an object affect whether or not it can float? Explain your answer.

• Finish Buoyancy lab (due 1/18)

  • Will it float?

    • • Density determines whether something will float in water or not.

      • Anything with a density greater than water's (1 g/mL) will sink, anything with a density less than that will float.

        • • Examples from lab - will they float?

          • Test in aquarium

          • Modeling clay has a density of 1.65 g/mL -- will it float? Can you form it into a shape that floats?

          • Large boats float, despite the fact that the metal they are made of is much more dense than the water, because their shape makes their volume much larger and include a lot of air.

          • Humans vary their densities by breathing

            • • With lungs full of air, our density is less than 1 and we float easily in water.

              • With empty lungs, our density is more than 1 and we sink in water.

          • Fish can change their density using a swim bladder

            • • inflate swim bladder to make them less dense, so they can rise in the water

              • deflate swim bladder to make them more dense, so they sink in water

          • Saturn

            • • m = 5.68 x 10^29 g.

              • V = 8.23 x 10^29 mL

              • D = 0.69 g/mL --- less than water! If we could find a big enough aquarium and dropped Saturn in it, it would float!

• Page 54: 1-3 due 1/14

  • Chemical properties

    • • Describe how a substance changes into a new substance, either by combining with other elements or by breaking apart into new substances

      • Examples

        • • Flammability - does something burn?

          • Reactivity - how easily does something react with other matter?

            • • Iron reacts with oxygen to make rust

              • Flour, water, and yeast react to make bread when heated

• Page 58: 1-7 due 1/14 (do on same page as P.54 problems)