Every earlier motor step lesson fixed step length at two metres and scanned force or step count; this scan holds those fixed and scans step length itself. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Every earlier motor step held step length fixed at two
Chapters five and six both kept step length at 2 metres and only ever varied force or step count. Here force stays 6 newtons and step count stays one, but step length itself shortens to 1 metre, giving per-step work 6 joules.
6⋅1=6
Step length itself decides how much a fixed force buys
Force and step count never change across these rows. Step length alone rescales the checked work-per-step arrow.
6⋅2=12
A longer step buys more work from the same force
At step length 3 metres, the same force gives per-step work 18 joules. Three rows separate step length from the force and step-count factors already scanned in chapters five and six.