Chapter Two: Science Skills

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

2. 2.1 Measuring mass • Mass describes the amount of matterin 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?

3. 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.

4. 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!

6. 2.1 Volume • Volume is the amount of space an object takes up. • The fundamental unit of volume in SI is the cubic meter (m3). • More convenient smaller units are cubic centimeters (cc or cm3), liters (L) and milliliters (mL).

7. 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.

8. 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.

9. 2.2 Density • Density describes how much mass is in a given volume of a material.

11. 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/cm3 or kg/m3.

13. 2.2 Density Density changes for different substances because: • Atoms have different masses. • Atoms may be “packed” tightly or loosely.

15. 2.3 Graphing • A graph is a visual way to organize data. • A scatterplot or XY graphis used to see if two variables are related.

16. 2.3 Graphing • A bar graphcompares data grouped by a name or category.

17. 2.3 Graphing • A pie graph shows the amount each part makes of up of the whole (100%).

18. 2.3 Graphing • A “connect-the-dots” line graph is often used to show trends in data over time.

20. 2.3 How to make an XY graph • Choose/label x and y-axis • independent variable = x axis • dependent variable = y axis • Make a scale • Most graphs use ones, twos, fives or tens • OR calculate the value per box • Plot your data • Seek the pattern- (best fit line) • Title of graph

22. 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.

23. 2.3 Identifying graph relationships • When there is no relationship the graph looks like a collection of dots. No pattern appears.

26. 2.4 Solving Problems

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

28. 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.

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

30. 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.