PRS DEMONSTRATION

1
PRS DEMONSTRATION

• Prior to this class, have you taken physics at
  either the high school or college level? (Note
  Do not count physical science courses as
  physics.)
• 1. Yes 2. No

2
Mastering Physics
Homework
Tutorial Applets
3
Physics 2211 Classical Mechanics

• Mechanics How and why things move.
• Describing motion (KINEMATICS)
• What causes (changes to) motion? (DYNAMICS)
• Classical
• Not too fast (v ltlt c)
• Not too small (d gtgt atom)
• Most everyday situations can be described in
  these terms.
• Path of baseball
• Orbit of planets
• etc...

4
Underpinnings of Science

• Models Simplification of Reality
• Reality is complicated.
• Models focus on whats important.
• (e.g., particle model)

• Measurements Anchors Models to Reality
• Reproducible, quantifiable experiments are
  crucial.
• Takes science beyond realm of individual
  experience

5
Tools of Mechanics

• Describing Mechanics Concepts
• Math
• Diagrams/Figures/Graphs
• Vocabulary/Technical Terms

• Motion Diagram

6
Mechanics Vocabulary

• Position and Time
• You Choose the
• Coordinate System

• Changes

Displacement

Time interval
7
(No Transcript)
8
Vectors...

• An arrow is commonly used to represent a vector
  quantity moreover, there are two common ways to
  symbolize a vector quantity
• Boldface notation A
• Arrow notation

A
9
Vector addition

• Consider the vectors A and B. Find A B.

B
B
A
A
A
C A B
B

• The Head-to-Tail Rule
• We can pick up and move vectors at will. Just
  dont change their length or their direction!!

10

• Which of the following corresponds to the
  diagram?
• 1. C B A
• 2. C A - B
• 3. C B - A
• 4. B C - A

B
11
Vector Subtraction
Displacement
12
Mechanics Vocabulary

• How fast?
• Speed

distance traveled

• Average Velocity

Rate of Change of Position
13
Mechanics Vocabulary

• Average Acceleration

Rate of Change of Velocity
14
Example 1.4 (Skier)
15
The motion diagram for a sprinter running around
a circular track (displacement vectors shown).
What is the direction of the acceleration at
point A?
(Select 9 to indicate the acceleration is zero.)
3
4
2
5
1
6
8
7
A
16
Circular Motion
17
Vocabulary of Mechanics

• Speeding Up vs Slowing Down

• Accelerate vs Decelerate

• Positive acceleration vs Negative
  acceleration

18
Kinematic Signs (Tactics Box 2.1)
19
Problem Solving Strategy (Example 1.10)
A rocket is launched vertically with an
acceleration of 30 m/s2. It runs out of
fuel after 30 seconds. What is its
maximum altitude?
20
Dimensions and Units...

• SI (Système International) Units
• mks L meters (m), M kilograms (kg), T
  seconds (s)
• cgs L centimeters (cm), M grams (gm), T
  seconds (s)
• British Units
• Inches, feet, miles, pounds, slugs...
• We will use mostly SI units, but you may run
  across some problems using British units. You
  should know how to convert back forth.

21
Converting between different systems of units
Useful Conversion factors 1 inch 2.54 cm 1
m 3.28 ft
22
Converting between different systems of units
Useful Conversion factors 1 inch 2.54 cm 1
m 3.28 ft
23
Dimensional Analysis

• An important tool to check your work. EASY TO
  USE!
• Example
• You do a problem and find for a distance d
• d vt 2 (velocity x time2)
• Units on left side L
• Units on right side (L / T) x T2 L x T
• Left units and right units dont match, so answer
  must be wrong!!
• Tip Dont do algebra with numbers.

24
More Tips

• Read !
• Before you start work on a problem, read the
  problem statement thoroughly. Make sure you
  understand what information is given, what is
  asked for, and the meaning of all the terms used
  in stating the problem.
• Watch your units !
• Always check the units of your answer, and carry
  the units along with your numbers during the
  calculation.
• Understand the limits !
• Many equations we use are special cases of more
  general laws. Understanding how they are derived
  will help you recognize their limitations (for
  example, constant acceleration).

25
Next Lecture
Kinematics Read Chapter 2