Objectives

• Explain Newton's three laws of motion
• Apply Newton's second law of motion to determine the acceleration of an object if the forces acting on the object are known
• Apply Newton's second law of motion to determine the net force acting on an object if the acceleration of the object is known
• Define impulse
• Define momentum
• Explain the relationship between impulse and momentum
• Describe the relationship between mass and weight

Isaac Newton (1642-1727)


Newton's Laws of Motion

Conservation of Momentum
L=mv

Money experiment (penny mass=2.5g, nickel=5.0g)

Elastic collisions: m_av_a = m_bv_b
m_au_a + m_bu_b= m_av_a + m_bv_b

Football collision

Coefficient of Restitution

Inelastic collisions: m_au_a + m_bu_b= m_av_a + m_b [e(u_a - u_b) + v_a]

Force affects motion

Measuring Ground Reaction Forces

Ground Reaction Forces in Walking and Running


Lunar Locomotion: How Do Weight and Inertia affect preferred movement?
Alter-g Treadmill: How Do Weight and Inertia affect preferred movement?

F=ma

When Force is Changing:

• Impulse = F_avg Δ t
  How do we calculate impulse?
  
  Soccer Kick Example (video)
  
  How does this work in a spreadsheet?
  
  

  Summary of Newton's Laws
  First law: Inertia (resistance to a change in motion)
  Second law: F=ma
  Third law: Action-reaction
  
  F=G(m₁m₂/r²)

  G=6.67300 x 10^-11m/kg/s²
  Mass of earth = 5.9742 × 10²⁴ kg
  Radius of earth = 6378.1 km

  G(m_earth/(r_earth)²)=?

  F=ma or W=mg
  
  How much does an astronaut weight?
  
  Questions:
  

  1. Can a body be moving if no external forces are acting upon it?
  2. Can a body change its direction of motion if no external forces act on it?
  3. Can a body be moving with constant velocity if external forces are acting on it?
  4. If you pull on a tug of war rope with a force of 50 lb, how much force does the rope exert on you?