Why does this displacement over time graph sloping down have a positive velocity? Intuition would tell me that if it slopes up its positive velocity and if it slopes down its negative velocity. Am I missing something about these graphs or is Khan Academy wrong?
I think it may be trying to catch you out by using the term "speed" instead of "velocity". Speed is a scalar quantity and represents the magnitude of the velocity, so it is always positive. The instantaneous velocity at 1 second is indeed -0.25 m/s, but the speed is 0.25 m/s