2. Chapter 2: Measurement and Units  2.1 Space and Time  2.2 Mass, Matter, and Atoms  2.3 Experiments and Data

3. Inv 2.3 Matter and Mass Investigation Key Question: How is mass described?

4. 2.3 Experiments and Data  Data are the measurements and calculations that you make during the experiment.  Things you measure in experiments are fundamental quantities.  Derived quantities can be measured but are often calculated from things you originally measured.

5. 2.3 Speed  Speed —is a derived quantity calculated from measurements of distance and time.  Other derived quantities include frequency, density, acceleration, intensity, and energy.  Each of these units can be broken down into combinations of the fundamental units of length, mass, and time.

6.  You are asked for speed in mi/h.  You are given speed in cm/s.  Relationships: —speed = distance ÷ time —1 hour = 3,600 s —1 mile = 1,609 m —1 meter = 100 cm Converting a speed from cm/s to mi/h  A car on a ramp is measured to go 45 cm in 1.5 s. What is the speed in miles per hour? 4.

7. 2.3 Area and volume  A solid object has surface area as well as volume.  Surface area —is the measurement of the extent of an object’s surface or area without including its thickness.

8. 2.3 Area and volume  Volume —is a measure of the space occupied by an object.

9.  You are asked for surface area and volume.  You are given the radius.  Relationships: area: A = 4π r 2 ; volume: V = (4/3)π r 3  Solve: Surface area Volume A= 4(3.14)(12.5) 2 = 1,963 cm 2 V= 4 (3.14)(12.5) 3 8,181 cm) 3 Calculating area and volume A basketball has a radius of 12.5 cm. Calculate the surface area and volume of the ball.

10. 2.3 Density  Density describes how much mass is in a given volume of a material.  The units of density are mass divided by volume.  Identically-sized cubes of iron, polyethylene, and glass contain different amount of mass.

11. 2.3 Density  Solids range in density from cork, with a density of 120 kg/m 3, to platinum, a precious metal with a density of 21,500 kg/m 3.

12. 2.3 Accuracy and precision  Accuracy —is the quality of being exact and free from error. —is how close a measurement is to the true value.  Precision —means how small a difference a measurement can show.

13. 2.3 Variables and relationships  Factors that affect the results of an experiment are called variables.  The science of physics can be thought of as “the search for the relationships between all the variables that describe everything.”  To learn about something specific in nature, scientists instead select a small set of related variables and define it as a system.

14. 2.3 Variables for a car on a ramp

15. 2.3 Experimental design  We do experiments to find out what happens when we change a variable.  The variable that is changed is called the experimental variable.  The variables that are kept the same are called the control variables.  When you change one variable and control all of the others, we call it a controlled experiment.  Controlled experiments are the best way to get reliable data.

16. 2.3 Experimental design  The procedure is a collection of all the techniques you use to do an experiment.  Your experimental technique is how you actually do the experiment.  Each repetition of the experiment is called a trial.

17. 2.3 Graphical data  A graph shows how two variables are related.  By convention, graphs are drawn a certain way.  The dependent variable goes on the y-axis which is vertical.  The independent variable goes on the horizontal or x-axis.

18. 2.3 Graphical models  A graph is a form of a mathematical model because it shows the connection between two variables.  A graphical model uses a graph to make predictions based on the relationship between the variables on the x- and y-axes.

19. 2.3 How to make a graph  Decide what to put on the x and y axes.  Make a scale by counting boxes to fit your largest value (multiples of 1, 2, 5 or 10 are best).  Plot your points.  Draw a best fit curve.  Create a title and label each axis.

21. 2.3 Recognizing relationships in data  When there is a relationship between the variables, a graph shows a clear pattern.

22. 2.3 Recognizing relationships in data  You can tell how strong the relationship is from the pattern.  If the relationship is weak, even a big change in one variable has little effect on the other.

23. 2.3 Recognizing relationships in data  When one variable increases and the other decreases, it is an inverse relationship.  Graphs of inverse relationships often slope down to the right.