- published: 18 Jul 2014
- views: 18845
Rolling resistance, sometimes called rolling friction or rolling drag, is the resistance that occurs when a round object such as a ball, tire, or wheel rolls on a surface. It is caused mainly by the deformation of the object, the deformation of the surface, and movement below the surface. Additional contributing factors include wheel diameter, forward speed load on wheel, surface adhesion, sliding, and relative micro-sliding between the surfaces of contact. It depends very much on the material of the wheel or tire and the sort of ground. What might be termed "basic rolling resistance" is steady velocity and straight line motion on a level surface, but there also exists rolling resistance when accelerating, when on curves, and when on a grade.
For example, rubber will give a bigger rolling resistance than steel on some surfaces (polished steel) and a lower rolling resistance on other surfaces (pavement/tarmac). Also, sand on the ground will give more rolling resistance than concrete. Any moving wheeled vehicle will gradually slow down due to rolling resistance including that of the bearings, but a train car with steel wheels running on steel rails will roll farther than a bus of the same mass with rubber tires running on tarmac. The coefficient of rolling resistance is generally much smaller for tires or balls than the coefficient of sliding friction.
tonight I'll dream a girl called home
and wake up in tears
all on my own
with the sun coming up
and my head against stone
balcony dressed and drawn
tonight I'll Dream a room so far away
frost pale blue
the colour of a perfect day
and then screw up my face
in the mirror
as I wait for the others to call
but if I don't believe in magic
and I don't believe in blood
and I don't believe in miracles
and I don't believe in love
then how come I believe so soon
in a cherry tree girl
and a dust blue room?
tonight I'll dream an hour so long
shadow soft smiles
and everyone loves me
to open my eyes
in a drag myself face undone
hard back into the world
tonight I'll dream a dream I dream
without even trying I'm flying I scream
as I practice the move
I spit at my pillow stained face
and the others all come
but if I don't believe in magic
and I don't believe in blood
and I don't believe in miracles
and I don't believe in love
then how come I believe it seems
in a girl called home