Introduction to Physics…. Unit 0: Review of basic science and math skills

What is physics? A branch of science that involves the study of the physical world…. Energy Matter How the two are related How things work Make observations Make predictions Use mathematics to explain physical observations and model them

Math Review…… Solving for variables….. In most problems you will be solving for one variable and given information for the other parameters of the problem. Try this: 2x + 10 = 44 Solve for t: v=d/t

Significant Figures….. All digits 1-9 are considered significant Sandwiched zeros are considered significant. Zeros at the end of a number with a decimal point are significant. Try this: How many sig figs are in the following…. 100001 102 2. 1.3 000001 0.002 0.02 1

For tests and class work purposes unless otherwise stated, your answers should be rounded to have 3 significant figures. Note: read instructions in syllabus for entering answers for online homework.

SI Units….Metric System….Measurement Physics involved working with measurements of many types and each type of quantity must be expressed in the appropriate units or combination of units. Distance, displacement or length: meter Mass: kilogram (kg) Time: second (m) Electric current: ampere (A) Temperature: Kelvin (K)

Many of the units in physics are Derived units… Many of the units in physics are Derived units….combinations of 2 or more base units. Acceleration: m/s/s or m/s2 Area: m2 Electric charge: Coulomb (C ) A•s Energy: Joule (J) kg•m2/s2 Force: newton (N) kg•m/s2 Frequency: hertz (Hz) s-1 Magnetic field: tesla (T) kg/A•s2 Velocity: m/s Volume: m3

Math and sig figs…. If adding and subtracting, answers should contain the fewest decimal places as the one with the least decimal places in the set. If multiplying and dividing, the answer should be expressed in fewest sig figs according to the number with the least in the set.

Converting…… Sometimes it will be necessary to convert from one unit to another in order to solve a problem. This may be within the metric system or between the metric system and English system. It’s a little harder from English unit to English unit because you have to know the equivalent unit and its often a different name. Ex. Feet to inches, ounces to pounds

In the metric system, the base unit for a given quantity stays the same and when you convert you are assigning prefixes that have a set quantity. Kilo-1000 Milli- 0.001 Example: grams to kilograms, meters to kilometers Everything in the metric system is based on 10.

Metric Practice….. G = F/B where B is measured in meters and F is measured in Newtons. What are the units of G? If G = B2F? If G = B-F If G = F3 K B

Practice on your own… The force of a magnetic field on a charged, moving particle is given by F= Bqv, where F is the force in kg•m/s/s, q is the charge in A•s, and v is the speed in m/s. B is the strength of the magnetic field, measured in teslas, T. What is 1 tesla described in base units?

A proton with charge 1. 60 x 10e-19 A•s is moving at 2 A proton with charge 1.60 x 10e-19 A•s is moving at 2.4 x 10e5 m/s through a magnetic field of 4.5 T. You want to find the force on the proton.

Dimensional Analysis….converting Conversion factor: an equivalent value that lets you convert between units Common equivalents 1 inch = 2.54 cm 1 mile = 1.61 km 1 kg = 2.21 lbs 1 lb = 4.45 N 1 cal = 4.184 J See page 911 in appendix D for more.

Convert….. Mad King Henry……… Helps you remember order of prefixes from smallest to largest Can also move the decimal Large to small---move decimal to left Small to large – move decimal to the right This works when you are doing Metric Conversions but not with English to metric or English to English.

How many seconds are in a leap year? How many miles in a 2 kilometers? Convert 43 km/h to m/s.

Convert the speed 5.30 m/s to km/h. Convert 2 minutes to seconds.

Scientific Method…. Gather background information Form hypothesis or question to be answered. Perform experiments/tests to collect data. Organize data. Analyze data. Conclusions. Re-test.

Taking measurements…. Experiments in physics usually involve taking measurements. A measurement is simply a comparison between an unknown quantity and a standard. Measurements be accurate and precise. Accuracy: how well the results of a measurement agree with the real value or the accepted value as measured by competent experimenters. For instruments, calibration against a standard is necessary to insure the validity of the measurements. Precision: degree of exactness; how close your measurements are to each other Significant figures in a measurement show its precision. A measure of 67.100g is precise to the nearest thousandth of a gram. The number of significant figures in a measurement is also dependent upon the instrument used to measure.

Data……. Many investigations in physics involve data collection and organization. Often scientists organize data using charts and graphs or diagram. One way to visualize or display data involving motion is to use graphs to show information from strobe pictures.

S T R O B E P I c s O sec 5 sec 10 sec 15 sec

Meterstick and Disc Activity Read your activity sheet. Obtain the materials from your teacher. Follow instructions carefully.

Variables…… Variable: any factor that might affect the behavior of an experimental setup. Independent variable: the factor that is changed or manipulated during the experiment. Dependent variable: the factor that depends on the independent variable

In an experiment, the length of a spring is tested using different masses. Construct a data table to represent this experiment. Collect data using a spring and 5 different masses. Graph your data. Draw a line of best fit. Identify the independent and dependent variables.

Linear relationships: y=mx+b The line of best fit is a straight line The dependent variable varies linearly with the independent variable Slope: ratio of the vertical change to the horizontal change Slope = rise /run or ∆y/∆x Nonlinear relationships: Quadratic: y=ax2 + bx + c (parabolic) One variable depends on the square of another Inverse: y=a/x one variable depends on the inverse of the other (a hyperbole)

Back to the strobe pics….. Strobe pictures can be used to represent motion. We can take the information from a series of strobe pictures and graph the data to show the relationship. You will need to establish an origin and a scale. Origin: beginning point Scale: units of measure, increments of measure

S T R O B E P I c s O sec 5 sec 10 sec 15 sec

Now graph it. Distance (m) 5 10 15 20 Time (seconds)

Motion at a constant rate Time = 0 s Figure 5 Time = 5 s Figure 6 Time = 10 s Figure 7 Time = 15 s Figure 8

t=0 sec t= 5 sec t=10 sec t= 15 sec Instead of drawing the picture over and over … Figure 9 t=0 sec t= 5 sec t=10 sec t= 15 sec

Now graph it. Distance (m) 5 10 15 20 Time (seconds)

To wrap up: Mathematics is an important part of a physics class. It is important to practice problems and ask questions in class. Often you will have to convert units so a good understanding of metric units is essential to success. Representing data is key to disseminating information about experiments. Data tables should have correct headings with units and a title. Graphs should have a title, labels on the x and y axis with correct units and data points indicated. Best fit lines should be drawn.

Assignment: math review set---come prepared for questions and Quiz. Accuracy and precision are vital to ensure validity of data. Results should be reproducible. Assignment: math review set---come prepared for questions and Quiz. Ticket out the door: One thing I learned……. One thing I have a question about……