2. Chapter 1: The Science of Physics Section 1: An Intro to Physics

3. Physics – the study of the interactions between matter and energy. Examples:  Why does an object fall toward the ground instead of floating?  Why does a rolling ball stop after a while.  How do engineers know how much weight an elevator can hold?

4. Classical Physics Mechanics ThermodynamicsAcousticsOptics Electromagnetism Newtonian Physics

5. Classical Physics

6. Modern Physics Nuclear Physics Aerodynamics Astrophysics Quantum Mechanics Relativity

7. Where did Physics begin? {Physis is Greek for “nature” Aristotle Nicolaus Copernicus (1473-1543) Galileo (1594-1642) Isaac Newton (1642-1727) Albert Einstein (1879-1955)

8. Obviously, physics involves the scientific method: Observing Hypothesizing Experimenting Drawing Conclusions ? data – a collection of recorded facts about an event. Some examples of data: The speed of a train. The amount of time an object falls. The amount of force applied to an object.

9. Hypothesis vs. Law vs. Theory  Hypothesis provides limited explanation  Theories explain phenomena based on observation  Scientific laws have been proven through repeated experimentation  describe natural phenomenon – not the how or why they work Throughout the course, we will come across various laws. We will perform experiments to verify them.

10. Symbols – used in formulas Unit – a quantity used to measure data.  Measurements are meaningless without units. Symbols: m - mass t - time F - force v - velocity W - work Here are some examples Units: kg kilograms for mass s seconds for time N newtons for force m/s meters/second for velocity J joules for work m meters for length Here are some examples Note that you will need to memorize the units because they are standard and cannot be changed. It is the unit that identifies what the quantity represents. Do not confuse symbols with units.

11. Base unit – a unit that cannot be broken down into other units.  Length/Distance: meter (m)  Mass: Kilogram (kg)  Time: second (s)  Temperature: Kelvin (K)  Electric Current: Amp (A)  Amount of a substance: Mole (mol)  Luminosity: candela (cd) Remember: Only these units are allowed in physics formulas! It is your responsibility to convert all quantities into basic units!

12. SignMagnitudePrefixUnit + or - Note that the prefix is optional (it may or may not be included) Remember that the standard unit for mass is the kilogram. Quantities numberkilometer Adding a prefix makes a unit larger or smaller. For example: One KILOmeter is equal to 1000 meters. One millimeter equals.001 meters.

13. Prefixes * * *

14. DERIVED Quantities Examples Velocity/Speed meters/second Length/Time Acceleration Length/Time/Time meters/second/second OR m/s m/s 2 OR Force Mass * Length/Time/Time kg * meters/second/second OR N derived unit – produced by combining multiple base units

15. Using the data you see, calculate how many feet are in one kilometer. Use dimensional analysis, and the fact that one mile is approximately 5280 ft and 0.625miles is one kilometer

16. Scientific Notation and Sig Figs

17. Scientific Notation Shorthand way to write really large or really small numbers Write 546000 in scientific notation: Write 0.000076 in scientific notation:

18. Accuracy vs Precision Accuracy – data is close to the true value  % error = l Your value – actual value l x 100 actual value Absolute value Precision – data measured repeatedly to obtain the same value Example

19. Accuracy & Precision Precision without Accuracy No Precision & No Accuracy Accuracy without Precision

20. Accuracy - Calculating % Error If a student measured the room width at 8.46 m and the accepted value was 9.45 m what was their accuracy? Using the formula: % error = (YV – AV) x 100 AV  Where YV is the student’s measured value & AV is the accepted value

21. Accuracy - Calculating % Error Since YV = 8.46 m, AV = 9.45 m % Error = l8.46 m – 9.45 m l x 100 9.45 m = -10.5 %  Note that the meter unit cancels during the division & the unit is %. The (-) shows that YV was low The student was off by almost 11% & must remeasure Acceptable % error is within 5%

22. Sig Figs Even though this ruler is marked in only centimeters and half- centimeters, if you estimate, you can use it to report measurements to a precision of a millimeter. Significant Figures Digits in a known measurement plus one uncertain digit Answer: 18.3 cm

23. Sig Fig Rules

24. Calculations with Sig Figs

25. Rounding Rules

27. The Science of Physics Representing Data

28. Consider this: What is the purpose of a graph? Graphs allow us to quickly view data and easily identify trends in data.

29. Our focus will be on line graphs. There are several different “relationships” that can be seen on line graphs. Linear

30. When experimenting, you will collect two types of data: independent variable – the factor that you change in an experiment. dependent variable – the factor that changes in response to the independent variable. Confused? How about an example…

31. Consider this: Carmen wants to determine if the amount of force an object hits the ground with changes when dropped from different heights.

32. If you were to graph Carmen’s results, where would you place the data? Generally, the independent variable is placed on the X axis, and the dependent on the Y axis. Of course, there may be some exceptions… Force Height

33. Now, on to the relationships. Suppose we plot several data points, shown on the graph. If we were to draw a “line” that best fits on top of those points, what kind of line would it be? A straight line, of course. best fit line – the line that can be drawn as close as possible to every data point on a graph.

34. In this case, the best fit line is “linear”. linear relationship – a scenario in which the best fit is a straight line. It is represented by the equation y = mx+b.  “b” is the y-intercept…the point where the graph crosses the y-axis.  It’s also the value of y when x=0. Slope is rise/run, or Δy/Δx. Sound familiar??

35. Of course there are non-linear relationships. Two of the most common are quadratic and inverse. quadratic relationship – one in which one variable depends on the square of another. The resulting graph is parabolic. It is represented by: y=ax 2 + bx + c

36. inverse relationship – a scenario in which one value increases as the other decreases (and vice-versa). The graph is a hyperbola. It is represented by: y = a/x

37. Graphing Hints Always title the graph… typically whatever is on the y axis vs the x axis Label the x and y axes What’s wrong with this graph??? 1.Points shouldn’t be connected 2.Scale is too small 3.Need units on the axes 4.Title