Presentation on theme: "NOTES—WHAT IS DENSITY? Density is the amount of mass per unit of volume; it describes how much matter is packed into a space."— Presentation transcript:
1 NOTES—WHAT IS DENSITY?Density is the amount of mass per unit of volume; it describes how much matter is packed into a space.
2 NOTES—WHAT IS DENSITY? Density is a characteristic property of matter A characteristic property does not depend on size (it will not change even if the amount of matter changes); therefore density is not dependent on the shape or amount of the substance1mL of water has a density of 1g/cm31000 mL of water has a density of 1 g/cm3It is used to identify one type of matter from another.The density of a pure substance is constant (at same temperature and pressure); it never changes.
3 CALCULATING DENSITY You need to measure an object’s mass and volume Density is calculated using the formula:Density = mass (g) ÷ Volume (mL or cm3)The basic unit for density is g/mL (liquid) or g/cm3 (solid or gas)D= mv
4 CALCULATING DENSITYWhen solving math problems, always show all work (even when using a calculator)STEPS:Rewrite the formulaSubstitute measurements into formulaSolve, circle, and label units
5 Calculating density practice MUST SHOW WORK Mass (g)Volume (cm3)Density (g/cm3 or g/mL)200200 mL50010 cm37001000 mL
6 SIZE AND DENSITY-- Does the density of a substance change if the amount changes? The density of a pure substance does not change if the size or amount changesFor example:Find the density of a wooden blockif mass=8g andvolume= 10cm3Density= ______If the block is cut in halfMass=Volume=Density =Did the density change?No, because the ratio of mass to volume is all relative
7 NOTES—WHAT IS DENSITY? Most dense least dense The more space between the atoms, the less dense the substance is.In general,solids are more dense than liquidsliquids are much more dense thangases, but less dense than solidsgases are the least dense of all
9 How can you tell if something will float or sink in a liquid? First, compare the density of the object/substance to the liquid it is in.If an object/substance is more dense than the liquid, it will sinkIf an object/substance is less dense than the liquid, it will floatIf an object/substance’s density is the same as the liquid, it won’t sink or float to the top; it will move toward the center of the liquid
10 How can you tell if something will float or sink in a liquid? The density of water is 1 g/mL.Do you know why ice floats on water?The density of ice is .92 g/cm3For example:certain types of wood have a density of .8 g/cm3, so they will float in water.Steel has a density of 7.8 g/cm3, so it will sink in water.See it in action:
11 Ships and boats are often made of steel. Why do they float on water?
12 How is density of matter effected by heat energy? As temperature increases, so does the amount of energyThe more energy a substance has:The more space between its moleculesThe less dense it isThat’s why…Solids are usually the most dense phase of matterThe molecules are tightly packed.Solids maintain (keep) definite shape and volume.The molecules don’t move around; they vibrateSolids have little energy
13 How is density of matter effected by heat energy? Liquids are less dense than solidsThere is more space between the moleculesLiquids do not have a definite shape, but do have definite volume.The molecules move slowly, sliding past one another; liquids have more energy than solidsAn exception to the rule: Ice is less dense than liquid water. Do you know why?
14 How is density of matter effected by heat energy? Gases are the least dense phase of matterThere is a lot of space between moleculesGases do not have definite shape or volume; they fill the container they are in.The molecules move very quickly; they have high energy.As the molecules gain heat energy, they move faster and will expand (spread apart)As the molecules lose heat energy, they move slower and will contract (move closer together)