Week 2: How Do You Measure a Feeling?
Floaty and heavy are feelings, not numbers. This week turns them into three measurements you can actually compare between jumps.
1 March 2027
Question#
Two people watch the same jump. One calls it floaty. The other calls it snappy. Both are describing something real, but neither has said anything a third person could check without watching the same clip — and “trust me, it felt floaty” is not a sentence the Jump Autopsy assessment in week 3 will accept.
This week is about the three measurements this course uses instead of adjectives:
- Height — the apex of the jump, measured relative to takeoff, not the bottom of the screen.
- Displacement — how far the character travelled horizontally by the time it lands, relative to takeoff.
- Airtime — the time from takeoff to landing.
Prediction (skip if you’d rather just look)#
If you hold an immediate-mode jump for longer, which of the three measurements do you expect to change? Which do you expect to stay the same?
Experiment#
Return to the home page and run five immediate-mode jumps: one very short press, three of increasing hold length, and one full hold. Record height and airtime for each. Plot them against each other in your head before you plot them on paper — do they grow in a straight line, or does the growth slow down as the hold gets longer?
Explanation#
Height and airtime aren’t independent: for a jump with no horizontal drift, they’re both consequences of one thing — your vertical launch speed at takeoff — passed through the same piece of physics twice. A longer hold (up to the point release stops adding speed) raises launch speed; launch speed sets both the apex height and how long gravity takes to bring you back down. That’s why they move together in your five trials, and why a course that teaches “gravity and launch speed” as one topic (week 4 onward) isn’t padding — they’re two knobs on the same underlying quantity.
Why airtime up and airtime down are usually equal
With constant downward gravity and no other vertical force, the time to rise from takeoff to apex equals the time to fall from apex back to takeoff height — the trajectory is symmetric in time. That symmetry breaks the moment something else touches vertical velocity mid-flight (a variable-height release, air control redirecting velocity, or landing on a platform above or below takeoff height), which is exactly what weeks 4–5 investigate.
Task#
Take your five-jump table from the experiment above and add a sixth column: predicted airtime, computed from height alone, before you look at the measured airtime for that row. (If height doubles, what do you expect airtime to do — double, more than double, less?) Then compare your predictions to what the trial actually reported, and write one sentence on where your intuition was wrong, if it was.
This is the exact structure the Jump Autopsy assessment scales up: a measurement table, a stated expectation, and an explanation that engages with where the two didn’t match.
Teaching team
- Idris Fenn — tutor