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