Mod 2: Dynamics

• Energy: the ability to perform work, calculated in Joules and is a scalar quantity
• Two main types of energy; KE (kinetic energy) and U (Gravitational potential energy)
• KE = 1/2mv², U = mg∆h
• Mechanical energy = KE+U or

  1/2mv²+mg∆h
• Work done against gravity =

  ∆U

  or U final-U initial

  or mg(final h-initial h)

  h also depends on the reference point
• To calculate change in KE,

  1/2mv²-1/2mu²
• Power is work done over time
• Power:

  W/∆t = ∆KE/∆t = Fscostheta/∆t
• Momentum = p = mv, meaured in kg*m/s
• Impulse is the change in momentum
• impluse = ∆p = m(v-u) = f*∆t
• What collision is this?

  Inelastic collision

  
• What collision is this?

  ELastic collision

  
• What collision is this?

  Explosive collision

  
• Conservation of energy (similar to Newton's third law) states that,

  initial forces/energy = -final forces/energy
• Conservation of momentum for elastic collisions:

  m1u1+m2u2 = m1v1+m2v2
• Conservation of momentum for inelastic collisions:

  m1u1+m2u2 = m1+2*v

  
  

  *The other way around for explosive collisions
• Conservation of Kinetic energy for elastic collisions:

  Σ1/2mu² = Σ1/2mv²
• For 2D collisions, simply do horizontal and vertical conservation of energy
• T=mg+ma when a mass is being lifted vertically upwards
• f*Δt is impulse, fcos(θ)/t is power