Crossword Genius

Travel using free energy (4)

Ross

I believe the answer is:

ride

'travel' is the definition.
(riding is a kind of travelling)

'free energy' is the wordplay.
'free' becomes 'rid' ('rid' can be a synonym of 'free'**).
'energy' becomes 'e' (physics symbol as in E=mci).
'rid'+'e'='RIDE'

'using' is the link.

(Other definitions for ride that I've seen before include "Go by bicycle" , "Eg, roundabout or roller-coaster, path for horses" , "Jaunt" , "Travel on the back of animal" , "Journey as passenger" .)

I've seen this clue in The Times.
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