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# What is Physics??

What is Physics??. The science of matter and energy and of interactions between the two. Physics is concerned with the description of nature – the description and explanation of natural phenomena in our physical world.

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## What is Physics??

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1. What is Physics?? • The science of matter and energy and of interactions between the two. • Physics is concerned with the description of nature – the description and explanation of natural phenomena in our physical world. • IOW: physics is concerned with how and why things work or behave the way they do!!

2. The Universe (or Nature) consists of… Matter, Energy, Space, and Time

3. How do we describe nature?? • Four Fundamental Quantities from which all other quantities are derived • LENGTH • MASS • TIME • ELECTRIC CHARGE (next semester!)

4. Units of Measure are used to describe these fundamental quantities There are different Systems or Conventions to flesh out these units of measure The most commonly used one in Science is the Systeme Internationale (SI) It is also known as the mks system

5. SI Units 1 kilogram weighs 2.2 pounds 1 meter is 3.3 feet long 1 second is 1 second in any unit system

6. Unit Prefixes Kilo (k) means multiply by 1000 1 kilogram (kg) = 103 = 1000 grams (g) Centi (c) means divide by 100 1 centimeter (cm) = 10-2 = 0.01 meter (m) Milli (m) means divide by 1000 1 millimeter (mm) = 10–3 = 0.001 meter (m) Other prefixes may be found on page 3 in your book.

7. Example Units behave like algebraic quantities. When identical units are divided, they cancel out. Convert 65 miles/hour to kilometers/hour: Angel Falls in Venezuela has a total drop of 979 m. Convert to feet:

8. Significant Figures • The number of digits whose values are know with certainty. • 5.5 feet 2 s.f. • 5.50 feet 3 s.f. • 1500 feet 2 s.f. • 1.500 x 103 4 s.f.

9. Group Problem Solving How many seconds are there in one day? Find out by converting 1 day into seconds, by canceling units.

10. Review of Trigonometry SOHCAHTOA H O  A For right triangles only!

11. Example SOHCAHTOA H O  A

12. Inverse Trig. Functions H O  A SOHCAHTOA

13. Example SOHCAHTOA H O  A

14. Pythagorean Theorem H O  A H2 = A2 + O2

15. Example SOHCAHTOA H O  A

16. Group Problem Solving The peak of Mt. Fuji in Japan is ~12,400 ft high. A person, several miles away, notes that the angle between the level ground and the peak is 30o. Find the distance (in feet) from the person to the point on the level ground directly beneath the peak.

17. Scalars and Vectors Vocabulary: Scalars are numbers Examples: 10 meters 75 kilometers/hour Vectors are numbers with a direction Example: 10 meters to the right 75 kilometers/hour north

18. Scalars and Vectors Scalar: 25 meters Vector: 25 meters north Scalar: 25 meters Vector: 25 meters east

19. Adding Vectors To add two vectors, A + B A B 1. place the head of one vector on the tail of the other vector B A 2. draw a new vector from the tail of the first to the head of the second B AC 3. This new vector is is called theresultant A+ B= C

20. Subtracting Vectors To subtract two vectors, A-B A B 1. Multiply vector B by -1: A + (-B) A -B 2. Then simply add A and -B, headtotail. -B A C 3. A + -B = C

21. The Components of a Vector P A = x + y We call x and y the components of the vector A. A y x O

22. Addition of Vectors(using Components) A+ B = C Add the x components of A and B to each other to get the x component of C. Then, add the y components ofAand B to each other to get the y component of C. C B A

23. Use Fig 1.20 from book herePage 13

24. Example You travel 2 km due East on 26th street, then turn right on Main street and head Southeast for 1 km, what are the components of your displacement?

25. Example B By Bx If B has a magnitude of 25 kilometers in a direction 30 degrees North of East, what is the x component of B? =30o

26. Group Problem Solving If A has a magnitude of 10 meters, and is pointing 45 degrees South of East, what is the magnitude (length) of the vector Ay? Ax  Ay A

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