Learning Goals  Explain the meaning of mass and describe the units for measuring mass.  Distinguish between mass and weight.  Define volume and explain how the volume of matter is measured.

 Key Question: How do you measure mass and volume? Measuring Mass and Volume

Measuring mass  Mass describes the amount of matter in an object.  The SI unit for mass is the kilogram (kg).  The kilogram is too large a unit to be convenient for small masses. One gram (g) is one-thousandth of a kilogram. What is the estimated mass of ONE zinc nut?

Matter  Matter is anything that has mass and takes up space.  All matter has mass.  Steel, plastic, rubber, and glass are different kinds of matter. A car has a lot more of each kind of matter than a bike.

Mass and weight are different  We tend to use the terms mass and weight interchangeably, but they are not the same thing.  Mass is the amount of matter in an object.  Weight is a measure of the pulling force of gravity on an object.

Mass and weight are different  A 2.3 kg bag of flour has a mass of 2.3 kilograms no matter where it is in the universe.  The weight of the bag of flour is less on the moon. The 5 lb bag of flour on Earth weighs only.8 lbs on the moon!

Volume  Volume is the amount of space an object takes up.  The fundamental unit of volume in SI is the cubic meter (m 3 ).  More convenient smaller units are cubic centimeters (cc or cm 3 ), liters (L) and milliliters (mL).

Volume  Measuring the volume of liquids is easy.  Pour the liquid into a graduated cylinder and read the meniscus at eye level.

Displacement  You can find the volume of an irregular shape using a technique called displacement.  Put the irregularly shaped object in water and measuring the amount of water displaced.

Comparing mass and volume  Mass and volume are two different properties of matter.  Size does not always indicate an object’s mass!  How the matter is packed into space is more important.

Learning Goals  Define density in terms of mass and volume.  Identify units used to express the density of materials.  Apply the density formula to solve problems.

 Key Question: How is an object’s density related to its volume, mass, and tendency to sink or float? Density

 Density describes how much mass is in a given volume of a material.

Density  Solids, liquids and gases are matter, so they all have density.  The density of water is about one gram per cubic centimeter.

Density  The units used for density depend on whether the substance is solid or liquid.  For liquids use units of grams per milliliter (g/mL)  For solids use density in units of g/cm 3 or kg/m 3.

Density of common materials  Density is a property of material independent of quantity or shape.

Density of common materials  Liquids tend to be less dense than solids of the same material.  Ex. solder (“sodder)

2.2 Density of common materials  Water is an exception to this rule.  The density of solid water (ice) is less than the density of liquid water.

Determining Density  To find the density of a material, you need to know the mass and volume of a solid sample of the material. 1.Mass is measured with a balance or scale. 2.Use the displacement method or calculate the volume.

Density Density changes for different substances because: 1.Atoms have different masses. 2.Atoms may be “packed” tightly or loosely.

Calculating Density 1.Looking for:  …the density of the candle 2.Given:  …mass = 1500 g; volume = 1700 mL 3.Relationship:  D = m/V # Sig. fig =.88 g/mL Solving Problems 4.Solution:  1,500 g ÷ 1,700 mL = g/mL