College Physics I Physics 1401 Fifth Class

1
College Physics I - Physics 1401Fifth Class

• Motion Ideas from Lab
• Historical Development of NM III
• Newton
• More on Motion Diagrams
• Introduction to Forces
• Definition of Force
• Types of Forces
• Contact Forces
• Long Range Forces
• Free Body Diagrams
• Lab Activity - Introduction to Forces

2
Motion Ideas from Lab

• What does zero acceleration mean?

a (m/s2)
t (s)
t (s)
3
Motion Ideas from Lab II

• What does constant positive acceleration mean?

a (m/s2)
t (s)
v (m/s)
x (m)
t (s)
t (s)
4
Motion Ideas from Lab III

• What does constant negative acceleration mean?

a (m/s2)
t (s)
v (m/s)
x (m)
t (s)
t (s)
5
Historical Development of Newtonian Mechanics III
- Newton

• 1642 - 1727 A. D.
• Newtons Three Laws of Motion
• First Law of Motion - Law of Inertia
• Second Law of Motion - Law of Changing Motion
• Third Law of Motion - Law of Mutual Interaction
• Law of Universal Gravitational Attraction

6
Newtons First Law of Motion

• If the net force acting on an object is zero,
  then
• An object at rest will remain at rest OR
• An object moving with uniform motion will
  continue to move at a constant speed in a
  straight line.
• Net Force 0 ? a 0 ? v constant
• At rest v 0
• Examples
• Uniform Motion v C
• Examples

7
Newtons Second Law of Motion

• If there is a non-zero net force acting on an
  object, then the object will change its motion.
• This change in motion will take one (or a
  combination) of the following forms
• The object will speed up (accelerate)
• The object will slow down (decelerate)
• The object will change direction
• Net Force dp/dt
• Net Force ma, if m is constant
• Examples

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Newtons Third Law of Motion

• When two objects interact with each other, they
  exerts forces on each other that are equal in
  magnitude, but opposite in direction.
• Examples
• Earth - Moon System
• Book on Table
• Others

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HDNM III - NewtonGravitational Force

• What causes the earth to rotate around the sun
  the moon around the earth?
• What causes objects to fall on the earth?
• Newton's relationship between these two ideas
• http//csep10.phys.utk.edu/astr161/lect/newtongr
  av.html
• Law of Universal Gravitational Attraction
• FG G (m1 m2 / r2) ur

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More on Motion Diagrams

• Air Glider Interactive Lecture Demonstration
• No Motion
• Constant Motion
• Accelerated Motion
• What is the acceleration at the top of the
  incline?
• The Elevator Problems

11
Introduction to Forces

• Definition of Forces
• In the past, a push or pull
• The mutual interaction between two objects
• Types of Forces
• Short Range or Contact Forces
• The two objects have to be touching each other
• We will be identifying 4 types of contact forces
  others exist
• Long Range or Action-at-a-Distance Forces
• The two objects do not have to touch each other
• We will be identifying 1 type of long range
  force 3 others exist in nature

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Introduction to ForcesShort Range or Contact
Forces

• Tensional or Compressional Force
• Tensional Force (FT) examples
• Compressional Force (FC) examples
• Frictional Force
• Kinetic Frictional Force (fk) examples
• Static Frictional Force (fs) examples
• Normal Force
• Normal Force (FN) Examples
• Forces Due to a Resistive Medium
• Air Resistance or Air Drag - FAR
• Water Resistance - FWR
• Others

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Introduction to ForcesLong Range or
Action-at-a-Distance Forces

• Gravitational Force (FG) - the force between
  objects that have mass
• Weight Force (FW)
• Electric Force (FE) - the force between objects
  that have an electric charge (or charges)
• Includes electricity, magnetism and molecular
  bonding
• Coulomb in late 1700s
• Maxwell in mid 1800s
• Strong Nuclear Force
• Weak Nuclear Force

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Free Body Diagrams Diagrams

• Introduction and Purpose
• Why Free Body Diagrams are Useful?
• Diagrammatic Representation of Forces
• Links to Newtons Second Law of Motion or First
  Law of Motion
• Procedure - Drawing Free Body Diagrams
• Identifying the OBJECT
• Sketch and Isolating the Object
• Identifying Short Range Forces - where the
  object touches the environment
• Identifying Long Range Forces
• Drawing the Force Vectors - both magnitude and
  direction
• Coordinate System

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Free Body Diagrams

• Handout
• At Rest
• Falling Freely
• On an Incline
• Moving at Constant Speed
• Moving with Acceleration
• Activity

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Next Class

• Homework to be Turned In
• Do Motion Diagram 2 Homework
• Discuss Free Body Diagrams and Newtons Laws of
  Motion
• Start Introduction to Forces Lab