Note: This is an ADVANCED HIGHER LEVEL topic. Although all may learn from it, only HL students will be tested on its content.
IB recommended length: 8 hours
If two spacecraft in deep space approach each other at constant velocities then who is to say if one is moving and the other is stationary, vice versa, or both are moving. It all depends on your point of view because all motion is relative. The concept of relativity was first explored by Galileo Galilei, writing in 1632 and using the example of a ship travelling on a smooth sea. Einstein's first modification of Galilean relativity, based on his realisations of the consequences of a finite speed of light, was first published in 1905.
In this advanced higher level topic we will at how observers in different frames of reference describe events in space and time. We will look at the differences between Galilean and Special relativity and the consequences of those differences. We will also introduce space-time diagrams and how we can use them to represent relativistic motion.
A reference frame is a set of coordinates at assign a location and time to an event. To represent our surroundings we generally use three spatial dimensions and one of time. For example we could define the time and location of an event in a classroom by measuring the distance along two walls at right-angles, the height above the ground and the time as indicated by a clock on the wall.
We can choose what location and system we want to use as the basis of our coordinate system, but an non-accelerating frame of reference is called an inertial frame of reference.
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