Lecture 2: Introduction to Physics 101

Chapter 1 : • The Conversion of Units (1.3) • Trigonometry (1.4) • Scalars and Vectors (1.5) Physics 101: Lecture 2, Pg 1

Length:

Distance

Radius of visible universe To Andromeda Galaxy To nearest star Earth to Sun Radius of Earth Sears Tower Football field Tall person Thickness of paper Wavelength of blue light Diameter of hydrogen atom Diameter of proton

Length (m)

1 x 10 26 2 x 10 22 4 x 10 16 1.5 x 10 11 6.4 x 10 6 4.5 x 10 2 1.0 x 10 2 2 x 10 0 1 x 10 -4 4 x 10 -7 1 x 10 -10 1 x 10 -15 Physics 101: Lecture 2, Pg 2

Time:

Interval

Age of universe Age of Grand Canyon 32 years One year One hour Light travel from Earth to Moon One cycle of guitar A string One cycle of FM radio wave Lifetime of neutral pi meson Lifetime of top quark

Time (s)

5 x 10 17 3 x 10 14 1 x 10 9 3.2 x 10 7 3.6 x 10 3 1.3 x 10 0 2 x 10 -3 6 x 10 -8 1 x 10 -16 4 x 10 -25 Physics 101: Lecture 2, Pg 3

Object

Milky Way Galaxy Sun Earth Boeing 747 Car Physics Student Dust particle Top quark Proton Electron Neutrino

Mass:

Mass (kg)

4 x 10 41 2 x 10 30 6 x 10 24 4 x 10 5 1 x 10 3 7 x 10 1 1 x 10 -9 3 x 10 -25 2 x 10 -27 9 x 10 -31 1 x 10 -38 Physics 101: Lecture 2, Pg 4

Conversion of Units

 Example: Distance Buffalo – Andromeda Nebula given in ly. What is the distance in km ?

1. Conversion factor: 1 ly=9.5 x 10 12 km 2. Insert conversion factor: d= 2 x 10 6 ly = 2 x 10 6 x 1 ly = 2 x 10 6 x 9.5 x 10 12 km = 1.9 x 10 19 km Remember: 10 a x10 b = 10 a+b 10 a /10 b = 10 a-b Physics 101: Lecture 2, Pg 5

Example:

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

Physics 101: Lecture 2, Pg 6

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 correct Physics 101: Lecture 2, Pg 7

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 !

Physics 101: Lecture 2, Pg 8

 x= ½ a t n . Find n ?

Example:

Physics 101: Lecture 2, Pg 9

Trigonometry

Right angle: Definition of sine, cosine and tangent: Sin q = h o /h Cos q = h a /h Tan q = h o /h a Pythagorean Theorem: h 2 = h o 2 + h a 2 Physics 101: Lecture 2, Pg 10

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 ?

Physics 101: Lecture 2, Pg 11

Scalars and Vectors

Physics 101: Lecture 2, Pg 12

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!

Physics 101: Lecture 2, Pg 13