Forget 3D printing and injection moulded plastics, my mate's a farmer and reckons he's growing organic, sustainable car parts. According to him it's really going well and this year's been a bumper crop.

A 1kg lump of plasticine travelling at 100 metres per second (over 200mph)  has the same momentum as a 100kg lump travelling at 1 metre per second (2 mph).

But if you were to collide, the latter would give you a nasty bruise while the former would probably rip you to pieces.