| what is a reference frame? | a point of view from which an observer can measure physical quantities such as distance velocity and time |
| what is an observer | someone who is viewing an event taking place |
| what is classical relativity | can be used to explain the motion of most objects in everday life
eg a ball kicked at 6ms-1 or a car driving at 70mph |
| what is relative velocity | involves the measuring of velocity by observers in different frames of reference |
| how do you calculate relative velocity when observers are moving towards each other | add the velocities |
| how do you calculate relative velocity if observes are both moving in the same direction | subtract the velocities to find the difference |
| can an object travel faster than the speed of light in any reference frame? | no |
| when we deal with objects moving at relativistic velocities (close to the speed of light), what type of relativity must we consider? | special relativity |
| what are relativistic speeds | speeds greater than 10 percent of the speed of light
non relativistic speeds are less than this |
| what is an inertial frame of reference | one that obeys newtons first law of motion |
| why is special relativity special | it deals with the special case of intertial frames of reference in which objects are either at rest or moving at constant speed relative to one another |
| what are einsteins two postulates of special relativity | the laws of physics are the same for two observers moving at a constant speed relative to one another
the speed of light in a vacuum is the same for all observers (nothing can travel faster than the speed of light) |
| what is the definition of time dilation | the apparent increase in time of an event for an object that is moving relative to an observer |
| what is the equation for time dilation | where t' is relativistic (dilated) time as measured by an observer in a different reference frame to the event
t is proper time as measured by an observer in the same frame of reference as the event
v is relative velocity in ms-1
c is speed of light in ms-1 |
| what is length contraction | the apparent decrease in length of an object that is moving relative to an observer |
| in what direction only does length contraction occur | it only takes place in the direction that the object is travelling |
| what is the formula for length contraction | where l' is relativistic length as measured by an observer in a different reference frame
l is proper length as measured by an observer in the same reference frame
v is relative velocity measured in metres per second
c is the speed of light measured in metres per second |
| explain why a greater number of pions are detected than you would expect if relativistic effects are not taken into account | the pions will have a far longer mean lifetime in our frame of reference
the pions will have a shorter distance to travel in their frame of reference |
