Laws of Attraction & NonContact Forces, Diffs bw/ Weight & M

• Non-Contact Forces = Laws of Attraction:

  • “Any 2 particles of matter attract 1 another with a force directly proportional to the product of their masses & inversely proportional to the square of the distance bw/ them”
  • Gravitational force [proportional to (check)] (m1 * m2) / distance^2
• Consider the force of attraction bw/ 2 students…

  • 2 students sitting 1.5 m apart
  • Student 1 = 50 kg
  • Student 2 = 70 kg
  • Gravitational force [proportional to (check)] (m1 * m2) / distance2
  • F = G x (m1 * m2) / l^2
  • ‘Big G’ Proportional constant = 0.000000000067

  
  

  • F = (6.7 x 10-11 m3kg-1s-2) * ((70 kg)(50 kg))/(1.5 m)2
  • F = 10422 x 10-11 = 1.04 x 10-7 N
• What about the attraction of the student to the earth?

  • Student 1 = 50 kg
  • G = 0.000000000667 m3kg-1s-2
  • F = G x (m1 * m2) / l^2

  
  

  • F = (6.7 x 10^-11 m3/kg/s^2) * ((5.97 x 10^24 kg)(50 kg)/(6.38 x 106 m)^2
  • F = 491 N Weight
• Weight = mass x gravity

  • W = m * g
• Are Weight & Mass the same thing?

  No
• Weight vs Mass:

  • An object's weight represents the force of attraction bw/ the earth & the object
  • Mass represents the quantity of matter of which body is composed
• Weight vs Mass:

  • F = (6.7 x 10^-11 m3/kg/s^2) * ((5.97 x 10^24 kg)(50 kg)/(6.38 x 106 m)^2
  • F = 491 N Weight
  • F = 491 N / 50 kg = 9.81 m/s^2 Gravitational pull = g
  • Weight = m x g
• Where does little g come from?

  • If you want Proof of Little g
  • Little g is the net acceleration that is imparted to objects due to the combined effect of gravitation (from distribution of mass within Earth) & the centrifugal force (from the Earth’s rotation)
  • Little ‘g’ = G * (mass of earth / l^2)
• Where does little g come from?

  • g = (6.7 x 10^-11 m^3/kg/s^2) * ((5.97 x 10^24 kg)(50 kg)/(6.38 x 106 m)^2
  • = - 9.81 m/s^2
• Why is this important?

  • The force acting on the body in relation to its mass is one of the most significant forces in biomechanics
  • Most consistent force acting upon us daily
  • No horizontal movement exists unless we overcome this force
  • All projectile motion is governed by gravitational forces
  • The mass of the Earth is unchanging, so if we reduce the mass of a body, it will be influenced less