L8 Introduction to Forces

Mechanics = Kinematics + Dynamics

Kinematics (Review)

1. Santa Claus's Crash Landing The old man has landed on the top of the roof of my house in Canada. Due to the large amount of ice on the roof, he starts to slide down the roof.Determine the vertical and horizontal speeds at which Santa Claus hits the ground using kinematic equations. (solution)
2. Simulations

   Motion Diagrams, v & a

   Special Case: Uniform Circular Motion

   Maze Game: Control ball by controlling r,v,a

3. Selected Problems.
   • 3.38 Buried Treasure
   • 4.59 Centrifuges

Dynamics

1. Key Relationships

Newton's 1st Law (define force: if no force, then no change in movement) $$ { { \mathbf { \vec F }_{net} } = 0 \, \rightarrow \, \Delta \mathbf { \vec v}} = 0 $$ Newton's 2nd Law (how an unseen force results in visible acceleration → defn. of mass) $$ \mathbf { \vec a } = { { 1 \over m }{ \vec F }_{net}}$$ Combining Forces $$ \mathbf { \vec F }_{net} = \sum \mathbf { \vec F }_{i} $$

2. Types of Forces

• Contact
  • Spring Force (Push or Pull) (F_sp)
  • Tension Force (Pull only) (T)
  • Normal Force (n)
  • Friction Force (f) -- opposite direction of motion
    • Kinetic
    • Static
  • drag (D) -- opposite direction of motion
  • thrust (F_thrust)
• Long Range
  • gravity
  • electric
  • magnetic

3. Free-Body Diagrams (including all the forces on an isolated body)

Knight Chapter 5 Lecture Slides: Force & Motion to Slide 58

4. Forces in 1D (104-1 Lecture 6)

5. Drawing Free Body Force Diagrams: From different student perspectives

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