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Chapter 2: Measurement and Units. 2.1 Space and Time 2.2 Mass, Matter, and Atoms 2.3 Experiments and Data. Inv 2.3 Matter and Mass. Investigation Key Question: How is mass described?. 2.3 Experiments and Data.
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Chapter 2: Measurement and Units 2.1 Space and Time 2.2 Mass, Matter, and Atoms 2.3 Experiments and Data
Inv 2.3 Matter and Mass Investigation Key Question: How is mass described?
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.
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.
Converting a speed from cm/s to mi/h • 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 • A car on a ramp is measured to go 45 cm in 1.5 s. What is the speed in miles per hour? 4.
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.
2.3 Area and volume • Volume • is a measure of the space occupied by an object.
Calculating area and volume • You are asked for surface area and volume. • You are given the radius. • Relationships: area: A = 4π r2; volume: V = (4/3)π r3 • Solve: Surface area Volume A= 4(3.14)(12.5)2 = 1,963 cm2 V= 4 (3.14)(12.5)3 8,181 cm)3 A basketball has a radius of 12.5 cm. Calculate the surface area and volume of the ball.
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.
2.3 Density • Solids range in density from cork, with a density of 120 kg/m3, to platinum, a precious metal with a density of 21,500 kg/m3.
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.
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.
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. 2.3 Experimental design
2.3 Experimental design • The procedure is a collection of all the techniques you use to do an experiment. • Your experimental techniqueis how you actually do the experiment. • Each repetition of the experiment is called a trial.
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.
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.
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 andlabel each axis.
2.3 Recognizing relationships in data • When there is a relationship between the variables, a graph shows a clear pattern.
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.
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.
