Physical ways to induce labour basically cover practical things you can do on your own (or with a partner) to help start labour.
The actual efficacy of any natural method of induction is very hard to prove or disprove. What kind of time lag after said activity does the start of labour have to begin to count as being induced by that activity? And what constitutes the start of labour? The odd contraction? A bit of a twinge? Waters breaking?
Clearly these methods pervade our culture because they seem to work but it could quite possibly be sheer co-incidence!
This works in 3 ways. Firstly, Semen contains prostaglandins which help to ripen the cervix for labour. Of course, a close second comes the bouncing and jiggling which will helps by getting baby’s head to bonk against the cervix which helps to get things started. Best not to mention to your partner though as it is not really the right kind of image to get you in the mood! Finally, mum having an orgasm will probably do the most because oxytocin – the major hormone associated with the start and progress of labour – is also produced through sex and intimacy (See also Nipple Stimulation, below). Even if it doesn’t work it is a nice way to pass the time…[1 , 2 and 3]
Probable efficacy: medium
It is unproven The key success here lies in mum enjoying it, but internal ejaculation and lots of bouncing will help! You might want to ensure you have appropriately absorbent bedding just in case you break your waters in the process (but it is not that likely!). Avoid if your waters have broken, or have had any bleeding or have a low lying placenta, or have been advised against sex for medical reasons.
This is a proven way to stimulate oxytocin. When a newborn suckles a nipple the action makes the pituitary gland produce oxytocin which is involved in the ejection of breastmilk (but interestingly not the production of it). By a lucky chance it is oxytocin that brings on labour (chemically induced labours in hospitals use synthetic oxytocin).
Probable efficacy: good
During labour it can enhance and intensify contractions, [4 and 5] and so the theory is sound that nipple stimulation before labour could potentially make it start. Basically unproven though it won’t hurt you. Some nice techniques outlined here but essentially can be done on one or both nipple, by hand, mouth or breast pump.
On a birth ball, or possibly in a car over some speed bumps or along an unpaved country road, or even doing jumps (subject to comfort). Well the jiggling may help open your pelvis and encourage baby to descend but the idea is really to stimulate the uterus to start contracting, and, like sex, get the baby’s head to bonk against the cervix to stimulate oxytocin and hopefully start the dilation a bit. It will certainly help you prepare for labour as bouncing is great urging labour, but not really to start it off. 
Probable efficacy: poor
Some people swear by it but frankly if your body is not ready then bouncing is unlikely to do anything. You can also rotate and move in any direction to encourage baby to descend. Some nice suggestions here. Just be careful not to be to vigorous and keep both feet on the floor – if you fall off you will do yourself more harm than good.
Again this takes the same philosophy as bouncing to open your pelvis and hopefully encourage baby to descend into the pelvis to make contact with your cervix and stimulate our old friend, oxytocin. You have to walk quite a lot and be a bit enthusiastic – a gentle amble round the block isn’t going to do much.
Probably efficacy: poor
Make sure you don’t tire yourself out so much that if you did go into labour you have no energy left to birth your baby! 
CUDDLING A NEWBORN
Skin-to-skin with your newborn is your body’s way of generating oxytocin which, in this instance, is one of the key hormones to start breastfeeding . As oxytocin is also key to stimulating labour, then if you manage to cuddle someone else’s newborn, ideally with a bit of skin-to-skin, then you might trick your body into oxytocin production.
Probably efficacy: medium. Basically unproven but a great excuse to cuddle a baby. Give them a good sniff for good measure (don’t you just love that new baby smell?)
This really comes under the same category as walking in that climbing stairs – or indeed any exercise that widens your legs, helps to open your pelvis and in combination with gravity, this helps baby to descend into a good position, and make contact with the cervix to stimulate oxytocin. Some people have found standing squats actually made their watrs break but this is undoubtedly because they were ready to break and just needed a little bit of pressure. 
Probable efficacy: medium
And will once again, be entirely dependent on how ready you are to go into labour. Watch your knees, hold the bannisters and make sure you don’t have slippery feet – falling down the stairs is a very BAD way to induce labour and could cause harm to you and your baby.
Yes well, this labour and birth business is a bit messy so probably best to get used to it. An enema will essentially stimulate the bowel to empty and, due to its proximity to the uterus, hopefully will encourage contractions to start.
Probably efficacy: poor
Best not done by yourself but here is how. The contents of the enema can vary from plain water to castor oil which has other inducing properties (see the post on Consuming Your Way to Labour) – but basically we think it is a bit drastic and awkward and doesn’t even guarantee you won’t pooh during labour so probably best to leave that rubber hose on the shelf. 
CONCLUSION TO PHYSICAL METHODS
Well, it seems pretty clear that physical methods will probably help get things started if you are almost there anyway, some of them are quite unproven and possibly no help at all.
So, back to the drawing board (or back to the intro post).
DISCLAIMER: Birthzang is a trained and FEDANT accredited antenatal educator but I am in no way recommending any of these methods to bring on labour. I list them here purely for information purposes and any activity undertaken by desperate and overdue readers is taken entirely at their own risk!
 This study shows sex makes no difference to helping labour start. http://onlinelibrary.wiley.com/doi/10.1111/1471-0528.12054/abstract;jsessionid=1EB57A9286EC46316E5484AFA82CFD23.f02t01
 This study showed it did help.
 But when they repeated study from  it found the reverse! http://www.ncbi.nlm.nih.gov/pubmed/19960160
 This study shows it can be beneficial but all the studies are a bit inconclusive due to widely differing methodologies.
 This study showed that there wasn’t really much efficacy but the studies were not really far-reaching enough to make clear conclusions.
 I couldn’t find anyone who had turned this into a study so remains entirely anecdotal.
WALKING  Again, no studies found.
CUDDLE A NEWBORN
 This study shows a link between skin-to-skin with a newborn and oxytocin release
http://www.ncbi.nlm.nih.gov/pubmed/11264623 however I couldn’t actually find any studies that looked at cuddling a newborn to help bring on labour. Perhaps I am googling the wrong thing!
 No studies found although midwives often encourage mums in labour to climb stairs to get things moving along so it will undoubtedly help open the pelvis.
 This study also looks at castor oil and was basically inconclusive, probably because it was trying to compare too many different things.