Chapter Two: Science Skills  2.1 Mass and Volume  2.2 Density  2.3 Graphing  2.4 Solving Problems

2.1 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?

2.1 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.

2.1 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!

2.1 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).

2.1 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.

2.1 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.

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

2.2 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.

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

2.3 Graphing  A graph is a visual way to organize data.  A scatterplot or XY graph is used to see if two variables are related.

2.3 Graphing  A bar graph compares data grouped by a name or category.

2.3 Graphing  A pie graph shows the amount each part makes of up of the whole (100%).

2.3 Graphing  A “connect-the-dots” line graph is often used to show trends in data over time.

2.3 How to make an XY graph 1.Choose/label x and y-axis  independent variable = x axis  dependent variable = y axis 2.Make a scale  Most graphs use ones, twos, fives or tens  OR calculate the value per box 3.Plot your data 4.Seek the pattern- (best fit line) 5. Title of graph

2.3 Identifying graph relationships  In a direct relationship, when one variable increases, so does the other. The speed and distance variables show a direct relationship.

2.3 Identifying graph relationships  When there is no relationship the graph looks like a collection of dots. No pattern appears.

2.4 Solving Problems

Calculate marble’s volume & density 1.Looking for:  volume, then density 2.Givens:  mass = 6 g, water displaced 30 to 32 mL 3.Relationships:  water displaced = marble volume, D = m/V 4.Solution:  32 mL – 30 mL = 2 mL  D = 6 g / 2 mL = 3 g/mL Solving Problems

2.4 How to solve design problems  Use what you know to design a solution that solves the problem.  Unlike “formula problems,” design problems have many correct solutions.  The solutions are only limited by your creativity, ingenuity, skill, and patience.

2.4 How to solve design problems  What does your design need to accomplish?  What constraints do you have?  Think of an idea.  Follow the design cycle…

Density and Ocean Currents  Did you know that there are underwater waterfalls in the ocean?  While it may seem strange for water to fall through water, it really happens due to density differences in ocean water coming from different sources.