Why are cricket bats smooth?

Question

I have noticed that the surface of cricket bats are smooth. What's the science behind it?

What would happen if the surface of the bat was rough? Would that increase our effort to play shots?

Answer 1

Cricket Bat surfaces are generally varnished (or oiled) to keep the wood with moisture which prevents Drying (and becoming Brittle) and eventually Breaking.
This varnishing gives the smooth finish.

In Contrast, Cricket Bat Handles are made rough to provide Holding grip.

One side effect of varnishing or smooth finishing is that the Direction (or angle) of the ball rebound (after hitting the bat) is more consistent.

The smooth (or glossy) finish will neither make the ball go further nor reduce the batting effort.

Answer 2

No references will be provided, but I will employ colloquial physics to support my claims.

This being said, the range of differences I describe between smooth and rough bat surfaces may not constitute reasons for cricket bats being smooth, but merely describe why a smooth mat might be more desirable than a rough bat. The differences in performance I describe are very small, which is why I will try to employ more extreme examples as a means of describing the forces at play.

1: Ball degradation.

This effect is relatively simple to comprehend. A more abrasive bat surface will - albeit to a much smaller degree - exert itself upon the ball in the same way a rough pitch surface will. Whereas a smooth bat will cause compression and distortion of the ball, a rough surface will also scratch and tear at the ball's surface. This in turn will cause the ball to wear more quickly and will reduce the performance of the ball more quickly, making it more difficult for bowlers to extract optimum movement for the same period of time as a less-abraded ball. Ball movement through the air will also be affected, as it will be more difficult for the bowler to maintain as great a difference between the smooth side of the ball and the rough side. This will impact swing and pace, as a rougher surface generates more friction in the air, slowing it down.

2: Ball rebound.

A rough bat surface will (albeit to a small degree) impact the velocity at which the ball rebounds from the bat's surface, lessening stroke power. This is because a the harder, rougher surface of the wood absorbs more of the softer ball's energy than a smooth surface would. To more easily conceptualise this, consider a ball that is struck by a board covered in sharp nails. The nails would pierce the ball, absorbing so much of the ball's energy that that ball would likely struggle to rebound off the nails at all. A rough bat surface is like a bed of nails, but at a much lesser degree. The rough edges of the wood will bite into the soft leather of the ball, absorbing ball energy. The ball then requires more energy to release itself from these tiny grooves and edges. Also, unless the bat stroke is perfectly opposite to the direction of the ball, these grooves and edges will also grip the softer leather, keeping it of the bat surface for longer, imparting a slight spin to the ball as the ball leaves the wood.

Clearly, the variations we're talking about here are minuscule, but real. The most important effect of those described above is that of ball degradation, which would happen significantly more quickly than with a smooth bat and would disadvantage bowlers.