My dad was in the navy and went overseas a lot. He went to new Zealand and brought back a Maori scalping club which was to be ornamental. However, it quickly became something which was used on me. It was affectionately referred to by my parents as, "The smacky bum stick". This is what it was:
Not that exact one but very similar. It's made of a single piece of solid heavy wood and was probably the size of a breadknife in length. Any sort of acting up would result in the smacky bum stick being used on me, and I mean this thing would be twatted across the backs of my legs and bare arse. I was strawberry floating terrified of it. (Was probably 6 or 7 at the time). I wasn't even a misbehaving kid.
Worse still was dad was away for months at a time, leaving mum on her own to look after me and my sister, who had started to figure out she could just say I'd done something and mum would go straight for me without question. I remember once we were both playing with my Lego, she got the hump about something and just shouted, "muuuum, Ad pulled my hair!" With a gooseberry fool eating grin on her face. Stomp stomp stomp here comes mum, grabs me by the back of the neck on my t-shirt and hit me with the club, then when I protested my innocence, threw me against the front door while my sister feigned tears. So that was nice. That sort of thing happend a lot.
Also when dad was back (and we'd move back to England at this point and I was about 12), she would shout and scream at him on a daily basis, blood curdling deep Harvey dent SAY IT volume shouting. Which always, and I mean always, would result in her then storming upstairs to take it out on me. This would normally take the form of just screaming at me for having an untidy room (I was 12 ffs and it was toys and lego). Luckily the club was gone by now, but I'd be a strawberry floating WRECK every time i heard an argument downstairs kick off, becuase I was always going to get the end of it. My sister's room was a gooseberry fool tip (she's a hoarder like dad was) but she never got so much as a telling off because she's so precious and speshul x. Even now if I feel an argument or something similar is brewing with me and my wife (which is no more than one of us saying something a bit twatty), I'll start tidying my side of the bedroom like some beaten dog, even though there's no need. It's Pavlovian.
Once I asked my dad why my sister got away with so much and had so much more attention given to her, he told me it's because, "she's brighter than YOU". He also used to mock me for being terrible at maths (I can barely count, I swear I've got some undiagnosed numerical mental condition), like he'd laugh in my face and take the piss out of me for asking for help with homework. If I couldn't do a mental arithmetic thing, I'd get this laugh, "OH dear
) and a head shake.
Oh and about 6 months before he died, he tried to put his hands down my pants in the pub. Which was nice.
Tldr: physical abuse leads to mental abuse, leads to more abuse.