Accumulations over time
Physics Narrative for 14-16
A repeated pattern
A central idea here, repeated often, is that accumulations over time lead to changes. To understand the structure of these changes clearly we need to be precise, and to use vectors.
The three central ideas in this episode are acceleration (→a), velocity (→v), position (→s).
Time is not used; instead we suggest
As you shift from vector to scalar descriptions, so you'll need to be careful that you don't drop or obscure essential elements. So we've suggested a restricted role for (average) speed, distance and duration.
Similarly, we've suggested that a recognition that all movement is relative movement is the key to avoiding ambiguity.
However, some things (for example, mass, force and acceleration) don't change as you switch point of view by adopting a new velocity – they're invariant – which provides a sound lead in to relativistic thinking, from Galileo to Einstein. Charlie, Alice and Bob have always agreed about force, acceleration and mass. That's because they've been helping you explore a Newtonian world. (In an Einsteinian world, they'd not even agree about durations and displacements, but that's for later study.)