DENSITY What weighs more? A 1,000 pounds of feathers, or a 1,000 pounds of lead? Density is defined as mass divided by volume. Mass is measured in grams (g); Volume is measured in milliliters (ml) or cubic centimeters (cc or cm3). 1 ml = 1 cc.

MASS vs. WEIGHT Mass is the amount of matter (particles) in an object. Weight is the amount of matter (particles) in an object, plus the gravitational pull. Gravity is defined as the pull towards the center of an object; such as the Earth, moon, etc.

The amount of space an object takes up. VOLUME The amount of space an object takes up.

Determining the Volume of a Regular Solid W L Volume = L • W • H

ARCHIMEDES QUESTION King Heron hired a goldsmith to make him a fancy crown of pure gold. The king wanted to know if this crown was made of pure gold or a mixture of gold and other metals, so he asked Archimedes (a Greek mathematician/scientist) to solve this problem. Explain (in detail) the procedure Archimedes used to solve the King’s dilemma.

VOLUME BY DISPLACEMENT (for objects whose shapes are not easily measured)

DENSITY OF WATER 1 milliliter (ml) = 1 cubic centimeter (cc) In the case of water, and water only: 1 ml = 1cc = 1g Therefore the density of 50 ml of water is: 1g/cc.

DENSITY PROBLEMS If the mass of an object is 25 grams, and it’s volume is 5 cubic centimeters, what is it’s density? 25 g / 5 cc = 5 g/cc If an object’s volume is 5 milliliters, and it’s mass is 2 grams, what is it’s density? 2 g / 5 ml = 0.4 g/ml

DENSITY PROBLEMS If the mass of an object is 125 grams, and it’s volume is 10 milliliters, what is it’s density? 125 g / 10 ml = 12.5 g/ml If an object’s volume is 2 milliliters, and it’s mass is 15 grams, what is it’s density? 15 g / 2 ml = 7.5 g/ml

Density • Predict which of the following will float: a penny, a piece of paper, an eraser, a small block of wood, a stone. • Write down your predictions. • Next to each prediction, write the reason for your prediction. • Compare your reasons. Is there a common factor that led to your prediction?

Density Substance Density (g/cm3) Wood 0.7 Corn oil 0.925 Plastic 0.93 Water 1.00 Tar ball 1.02 Glycerin 1.26 Rubber washer 1.34 Corn syrup 1.38 Copper wire 1.88 Mercury 13.6

BUOYANCY • Buoyancy- the ability of an object to float. • Archimedes Principle- An object will float when the mass of the object is less than the amount of liquid it displaces.

SUBMARINES

BUOYANT FORCE

Buoyancy Floating and Sinking Position of Object Weight vs. Buoyant Force Floating at surface Sinking Suspended under water Buoyant force greater Weight greater Forces balanced