- 
  
  Was the first scientist to provide an explanation for observations of the movement of planets within the solar system.
- 
  
  Was a scientist, philosopher, and mathematician. His observations of the movement of objects on Earth led him to conclude that all objects accelerate as they fall.
- 
  
  Gravity is a function of space, time, energy, and mass. According to the model developed by Albert Einstein (1879–1955), time and space are intricately related.
