The rolls apply pressure on the flat strip in order to reduce its thickness, resulting in
a roll force, F, as shown in Fig. 13.2c. Note that this force appears in the figure as
perpendicular to the plane of the strip, rather than at an angle. This is because, in
practice, the arc of contact is very small compared with the roll radius, so we can assume
that the roll force is perpendicular to the strip without causing significant error
in calculations. The roll force in flat rolling can be estimated from the formula