Lecture 2: Introduction to Physics 101

1
Lecture 2 Introduction to Physics 101

• Chapter 1
• The Conversion of Units (1.3)
• Trigonometry (1.4)
• Scalars and Vectors (1.5)

2
Length

• Distance Length (m)
• Radius of visible universe 1 x 1026
• To Andromeda Galaxy 2 x 1022
• To nearest star 4 x 1016
• Earth to Sun 1.5 x 1011
• Radius of Earth 6.4 x 106
• Sears Tower 4.5 x 102
• Football field 1.0 x 102
• Tall person 2 x 100
• Thickness of paper 1 x 10-4
• Wavelength of blue light 4 x 10-7
• Diameter of hydrogen atom 1 x 10-10
• Diameter of proton 1 x 10-15

3
Time

• Interval Time (s)
• Age of universe 5 x 1017
• Age of Grand Canyon 3 x 1014
• 32 years 1 x 109
• One year 3.2 x 107
• One hour 3.6 x 103
• Light travel from Earth to Moon 1.3 x 100
• One cycle of guitar A string 2 x 10-3
• One cycle of FM radio wave 6 x 10-8
• Lifetime of neutral pi meson 1 x 10-16
• Lifetime of top quark 4 x 10-25

4
Mass

• Object Mass (kg)
• Milky Way Galaxy 4 x 1041
• Sun 2 x 1030
• Earth 6 x 1024
• Boeing 747 4 x 105
• Car 1 x 103
• Physics Student 7 x 101
• Dust particle 1 x 10-9
• Top quark 3 x 10-25
• Proton 2 x 10-27
• Electron 9 x 10-31
• Neutrino 1 x 10-38

5
Conversion of Units

• Example
• Distance Buffalo Andromeda Nebula given in ly.
  What is the distance in km ?
• 1. Conversion factor 1 ly9.5 x 1012 km
• 2. Insert conversion factor
• d 2 x 106 ly 2 x 106 x 1 ly 2 x 106 x
  9.5 x 1012 km
• 1.9 x 1019 km
• Remember 10a x10b 10ab
• 10a/10b 10a-b

6
Example

• Speed limit on german autobahn is 130 kmh. What
  is the speed limit in mph ?

7
Lecture 2, ACT 1

• A very good fastball pitcher can throw the ball
  100 mph. What is the ball speed in m/s?
• 1 - 450 m/s
• 2 - 45 m/s
• 3 - 0.045 m/s

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Dimensional Analysis

• Dimension indicates the nature of a physical
  quantity or the type of unit.
• Example
• Dimension of distance is length L
• Unit of distance is m , km, miles,
• Note
• Dimensions of left-hand side and right-hand side
  of an
• equation have always to be the same, e.g. when
  you start with
• a quantity of dimension length you have to finish
  with one
• of dimension length.
• Powerful check of your computation !

9
Example

• x ½ a tn. Find n ?

10
Trigonometry
Right angle
Definition of sine, cosine and tangent
Sin q ho/h Cos q ha/h Tan q ho/ha
Pythagorean Theorem h2 ho2 ha2
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Example

• A certain mountain road is inclined 3.1 degrees
  with respect to the horizon. What is the change
  in altitude (in meters) of the car as a result of
  its traveling 2.90 km along the road ?

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Scalars and Vectors
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Lecture 2

• Units
• Dimensional Analysis
• Trigonometry
• Scalars and Vectors

I strongly suggest that you try the example
problems in the textbook. If you have trouble
with any of them, please go to office hours for
help!