How to Understand Relativity

All measurements of physical properties that are stationary relative to an observer are the same as in Newtonian physics and are referred to as proper measurements. Relativistic measurements, on the other hand, involve measuring the properties of objects in motion. For example, if you observe a person sipping a cup of coffee in a high-speed spacecraft, you would perceive his actions as slowed down. However, if you were in the same spacecraft, you would perceive his behavior as normal, since both you and the person are moving at the same speed.