Computing Density Density = mass (g) volume (cm 3 ) DETERMINE VOLUME: DETERMINE MASS: RT = Pg. 1
Computing Density DETERMINE VOLUME: Another way to determine volume is to measure the height, length and width of a solid that is cubic or rectangular in design. The formula shown will determine the volume of the object.
Sample Density problem #1 A student determines the mass of a rock sample to be 156.3 g. The volume of the same rock sample is 51.3 cm 3. What is the density of the rock sample? Density = mass (g) volume (cm 3 )
Sample Density problem #2 Given the information provided, determine the density of the toy? Mass of Toy Dinosaur = 10 g Volume of Toy Dinosaur = ? Density = mass (g) volume (cm 3 )
Determining Relative Density The densities of objects in gases and fluids can be determined by observing the “flotation” of the object in the fluid or gas Density of helium gas = 0.2 g/cm 3 Density of air= 1.2 g/cm 3 Objects with lower densities than the fluid or gas they are in will float above objects with higher densities.
Liquid water has a density of 1.0 g/mL. Determine the relative densities of the objects in the glasses of water. Determining Relative Density
Physical Changes That Affect Density If temperature of a gas increases while pressure is constant… Changes in temperature and pressure can change the densities of substances …. especially gases. Example: Air that is heated is less dense than air that is cooled. Therefore, heated air will rise above cooled air.
Physical Changes That Affect Density Changes in temperature and pressure can change the densities of substances …. especially gases. If temperature of a gas decreases while pressure is constant… Example: Air that is cooled is more dense than air that is heated. Therefore, cooled air will sink below heated air.
Physical Changes That Affect Density Changes in temperature and pressure can change the densities of substances …. especially gases. If the pressure on a gas increases while the temperature is constant… Pressure
Phases of Matter and Density Matter on Earth exists in three phases: solid, liquid, gas. Liquid Iron = 7.2 g/cm 3 Solid Iron = 7.8 g/cm 3 Ice = 0.97 g/cm 3 Liquid Water = 1.0 g/cm 3
Density vs. Object Size and Shape The density of an object will NOT change should an object change its size and/or shape. Quartz crystal: Mass = 10.9 g Quartz globe: Mass = 88..9 g Density of quartz 2.6 g/cm 3