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level: Special Relativity

Questions and Answers List

level questions: Special Relativity

QuestionAnswer
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 observersomeone who is viewing an event taking place
what is classical relativitycan 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 velocityinvolves the measuring of velocity by observers in different frames of reference
how do you calculate relative velocity when observers are moving towards each otheradd the velocities
how do you calculate relative velocity if observes are both moving in the same directionsubtract 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 speedsspeeds greater than 10 percent of the speed of light non relativistic speeds are less than this
what is an inertial frame of referenceone that obeys newtons first law of motion
why is special relativity specialit 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 relativitythe 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 dilationthe apparent increase in time of an event for an object that is moving relative to an observer
what is the equation for time dilationwhere 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 contractionthe apparent decrease in length of an object that is moving relative to an observer
in what direction only does length contraction occurit only takes place in the direction that the object is travelling
what is the formula for length contractionwhere 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 accountthe 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