Chemistry TAKS Preparation November 3, 2003

Henry Ford If you say you can, or you can’t, you’re right.

Today’s Concepts n Density n Buoyancy n Viscosity n These are some “Physical Properties” which can be observed or measured without changing the composition

Density n how heavy something is for its size n Ratio of mass to volume – –Found by dividing the mass by volume – –D = m (When dividing, the top number V goes into the calculator 1st) – –Water has a density of 1 g/mL – –Density is not changed by sample size n If the density of substance is less than its surroundings, it floats

Sample Problems n n A piece of wood has a mass of 12 g and a volume of 16 cm 3. What is its density? n n At 20°C, Steel has a density of 7.8 g/cm 3. What is the mass of 56 cm 3 of steel? n n If the steel was cut in half, would the density be 1/4, 1/2, 2 times, or the same?

Buoyancy n David Letterman’s “Will it float?” n How do steel ships float if steel doesn’t? n n Archimedes' Principle – –A body wholly or partially immersed in a fluid will be buoyed up by a force equal to the weight of the fluid that it displaces. n n Do demo now.

Viscosity n The resistance to flow is the viscosity of a substance. –Heinz ketchup is more viscous than milk. n Viscosity is affected by temperature. –Warm syrup is less viscous than cold. n Related to car oil commercials.