You have probably heard the old trick question,

1. You have probably heard the old trick question, • “Which is heavier? • A pound of feathers or a pound of bricks?”

2. Why do you think so many people blurt out the answer “bricks”? • Why do the bricks seem heavier?

3. Now take a look at the empty balance • Imagine that on the right side of the balance you are going to place a pound of bricks. How much space would they occupy? • Now, imagine placing a pound of feathers on the left side. How much space would they occupy?

4. So what is the biggest difference between a pound of feathers and a pound of bricks? • Space occupied by each of them

5. 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? If 6 zinc nuts have the mass of 96.2g.

6. 2.1 Matter • Matteris 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.

8. 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.

9. 2.1 Mass and weight are different • A 2.3 kg bag of flour has a massof 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!

11. Mass and weight in our solar system

12. 2.1 Volume • Volumeis 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). vid

13. 2.1 Volume • Measuring the volume of liquids is easy. • Pour the liquid into a graduated cylinderand read the meniscus at eye level.

14. Volume of a solid Measurment • Water Displacement By measuring: Length x Width x Height What if you can not measure it easy?

15. 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.(Displace is the same as moved.) • It was 50mL and then it moved to 53mL as the key was added. Diff. 3mL

16. 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. • On to Density

17. Density 2.2

18. Density describes how much mass is in a given volume of material • Density = Mass/Volume • ALL matter (gases included) have density

19. Units of Density • Typically, the units of density are grams per milliliter (g/mL) • Sometimes, you will see g/cm³ • 1mL = 1cm³

20. Densities of common materials • High densities (lots of mass in a small amount of space): Platinum (21.5 g/cm³), Lead (11.3 g/cm³), and Steel (7.8 g/cm³) • Small densities (small amount of mass in a large amount of space): Air (0.0009 g/cm³), Pine wood (0.44 g/cm³), and Ice (0.92 g/cm³)

21. Density is an Identifying Property • Density of a material is the same no matter what the size or shape of the material

22. What does density tell us? • How tightly “packed” the atoms or molecules of a particular material is. • Example: • Diamond is made of carbon atoms and has a density of 3.5 g/cm³ • Graphite is also made of carbon atoms and has a density of 2.09 g/cm³. • Which of these has atoms that are MORE tightly packed??

24. 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.

25. 2.3 Graphing • A bar graphcompares data grouped by a name or category.

26. 2.3 Graphing • A pie graph shows the amount each part makes of up of the whole (100%).

27. 2.3 Graphing • A “connect-the-dots” line graph is often used to show trends in data over time.

28. 2.3 How to make an XY graph • Scatterplotsshow how a change in one variable influences another variable. • The independent variable is the variable you believe might influence another variable.(X axis Left and right) • The dependent variable is the variable that you hope will change as a result of the experiment.(Y axis Up and down)

29. 2.3 How to make an XY graph • Pressure is critical to safe diving. • How does an increase in depth affect the pressure? • What sort of graph would best show the relationship between pressure and depth?

30. 2.3 How to make an XY graph • Choose x and y-axis • Depth is the independent variable = x axis • Pressure is the dependent variable = y axis • Make a scale • Most graphs use ones, twos, fives or tens • OR calculate the value per box • Plot your data • Create a title * Exception- when time is a variable Time is always on the bottom!!!

32. 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.

33. 2.3 Identifying graph relationships • When there is no relationship the graph looks like a collection of dots. No pattern appears.

34. 2.3 Identifying graph relationships • In an inverse relationship, when one variable increases, the other decreases.

35. 2.3 Reading a graph What is the speed of the car at 50 cm? • Find the known value on the x axis • Position = 50 cm • Draw a line vertically upward from 50 cm until it hits the curve. • Draw a line across horizontally to the y-axis from the same place on the curve. • Read the speed using the y axis scale. • Speed = 76 cm/s