Newtons Law

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Newtons Law

• Change ----motion
• Two questions
• ? How do we describe motion?
• We want to analyze the motion mathematically
• The mathematical description of motion is called
  kinematics.
• ? How do we explain motion?
• The explanation of motion in terms of its causes
  is called dynamics.

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Concepts of Motion

• 1.1 Motion Diagrams
• 1.2 The Particle Model
• 1.3 Position and Time
• 1.4 Velocity
• 1.5 Acceleration
• 1.6 Examples of Motion Diagrams
• 1.7 From Words to Symbols

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Suggest to practice
Stop to think 1.1 P5 Stop to think 1.2 P6 Stop to
think 1.3 P13 Stop to think 1.4 P15 Stop to think
1.5 P28 Example 1.2 P 12 Example 1.4 P
16 Example 1.6 P 17 Example 1.8 P 22 Example
1.9 P 23 Example 1.10 P 27
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1.1 Motion Diagram

• Motion is defined as the change of an objects
  position with time
• The right picture is showing a car positions at
  several equally spaced instants of time. It is
  motion diagram

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I
Object moving with constant speed
Ball slowing down as it rises And speeding up as
it falls
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1.2 Particle Model
Particle model of motions is a simplification in
which we treat a motion object as if all of its
mass were concentrated at a single point.
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1.3 Position and Time
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Change in Position
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Vector and Vector addition
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Application to Motion Diagrams
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Velocity
In Physics the distinction between speed and
velocity is very important. Speed is scalar (how
fast) velocity Is vector (how fast and in which
direction).
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Motion diagrams with velocity vector
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Motion diagram of a ball
The average velocity vectors are found by
connecting to dots with arrows.
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Relating position to velocity
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Acceleration

• Average acceleration

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A particle undergoes acceleration which
moving from 1 to point 2. Which of the choice
shows the velocity
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Examples of Motion Diagrams

• Please practice examples 1.4---1.8
• (page 1820).

Example 1.4 Skiing through the wood
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Position vs time graphs
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From Words to Symbols

• Sketch the situation
• Establish a coordinate system
• Define symbols. ex.
• List known information
• Some quantities are implied by the problem,
  rather
• than explicitly given. Others are determined by
• your choice of coordinate system.
• ?Identify the desired unknowns

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Units and significant figures

• Three basics SI unit

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Convert the following to SI units

• 60mi/h
• Alcohol mass density
• 0.81g/cm3