the weak form of 'on'

I am confused at whether or not there is a weak form at preposition's 'ON'. I've checked at some dictionaries at Cambridge and Oxford dictionary, they don't mention on the weak form's pronunciation. However, I, am a Japanese, checked at English-Japanese dictionaries, they mention on the weak form as /ən/.

For example, is there the difference of pronunciation between 'It goes on' and 'There is an apple on the table' in connected speech?

Does it exist?

Thanks Yuichi

*It's Edited

Solution 1:

If you reduce 'on', you get syllabic 'nn', which is the same as you get when you reduce 'in'. Since there are many contexts where either is possible, to avoid clashes, we refuse to reduce 'on': no matter how low the stress, the vowel quality will always remain.
Of course, we could have chosen to do this to 'in' instead. But it's a question of conserving energy, 'in' being much more common, and also a common prefix.
Contrary to what has been stated above, I don't think that one on one will have a reduced on because that can too easily be confused with one and one.
As an aside, Yuichi, I am impressed with how acutely Japanese speakers hear English, being able to distinguish subtle differences most native speakers miss.