8/31/10

Post date: Aug 31, 2010 3:1:34 PM

Bell Ringer: What determines whether something sinks or floats?

• Buoyancy lab (due 9/1)

  • 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 Monday

  • 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 Monday