Class 3

Hi, Students!  Keep up the good work!  You're making progress with a new and difficult subject! Check the bottom for homework and any other handouts.

WED 2 PM***PARENTS -PLEASE CHECK YOUR EMAIL FOR HELP ON HOMEWORK 2**

THU 1 PM***For help with questions 3., 4., and 5. in next weeks Homework 3 (Class 3 - Handout 3A-- click below) you should use GOOGLE.  EXAMPLE:  Question 3: try Googling something like "names of planets."

Here is the link to the ARCTAN calculator.  Remember, O is "theta", the angle you want!
Go to  http://calculator.tutorvista.com/arctan-calculator.html    to get the program.

To get the angle, O, in degrees, put the value you get for Ry/Rx into the ARCTAN calculator.

NOTE - there is a problem in ARCTAN when Rx or Ry or both are NEGATIVE NUMBERS.  You MAY get the answer pointing exactly in the opposite direction from the correct answer.  If this happens, just add 180 degrees to the angle in the calculator, and you should be right.
EXAMPLE: You get -20 degrees (and you see it should go in the opposite  direction), you add 180 and now have 160 degrees (-20 + 180 = 180 - 20 = 160).  Now you see everything lines up right. 

From now on in this blog, we'll use   \/X\   =  square-root of X    and    X2 = X squared

Want to find the magnitude of a vector, like R?  The magnitude of R is R.  To get it use:
           R  =   \/(Rx2  +  Ry2)\   (First do squares, then add them, then take square-root)

So, the vector equation  R = Rx + Ry is RIGHT, but the scalar eq'n  R = Rx +Ry is WRONG.
( To make it right, you need to use the squares and square-root!!)
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EXAMPLE:    Find R and O, if  Rx = 5, and Ry =12 [can write as:  (Rx, Ry) = (5, 12) ]

1) FIND R:     R =  \/(52  +  122)\  =   \/(25 + 144)\  = \/169\ = 13     So,  R  = 13

2) FIND O:    O = ARCTAN(Ry/Rx) = ARCTAN(12/5) = ARCTAN(2.4)
Putting 2.4 into ARCTAN calculator get 67.38 degrees.       So,  O  = 67.38 degrees
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BASIC EQUATIONS TO GET R and O if you know Rx and Ry !      

                   R  =  \/(Rx2 + Ry2)\         <==  Don't forget square and square-root parts
                   O  =  ARCTAN(Ry/Rx)        <==  Ry comes first
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  Hope everything works for you!

Mr. Frank

https://sites.google.com/site/yhbscience/Class3.Handout3A--Homework.Vectors.and.the.Universe.docx?attredirects=0&d=1