acceleration

["geoff dawson" <geoffrey.dawson@aph.gov.au>]

'Acceleration' can mean not only 'getting faster while travelling in a
straight line' (what we think of mostly) but also 'moving at constant speed
on a curve'.
Does anyone know a formula to relate the radius of a curve, the speed of the
train and the acceleration?
Ie a train travelling at a constant speed x m/sec around curve radius y
metres experiences an acceleration of how many m/sec/sec?
Thank you.
Geoff Dawson in Canberra.