Newton's Law of Universal Gravity

When an apple falls on my head, my first thought it “ouch!” But not Sir Isaac Newton. By his time, people already understood the concept that gravity makes things fall, but Newton showed that gravity is in fact a universal principle, that ALL objects had a gravitational pull to each other. The force of that pull was directly related to the objects mass. The Earth has far more mass than the apple so it pulls the apple towards it, but the apple is also exerting a small gravitational force upon the Earth, too.

The equation to calculate the force of universal gravitation between two objects is: 

F=G{\frac {m_{1}m_{2}}{r^{2}}}\
where “G” is the universal gravitation constant of 6.67×10-11 Nm2/kg2 
“m1” is the mass of object 1
“m2” is the mass of object 2
“r” is the distance from the center of object 1 to the center of object 2.

Newton's Laws of Motion

The laws of motion haven’t changed much in the last 300 years. In 1686, twenty years after his revelation of gravity, Newton published his laws that govern all motion:

  1. Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.
  2. Force is equal to the change in momentum per change in time. For a constant mass, force equals mass times acceleration.
  3. For every action, there is an equal and opposite reaction.