S. M. R. A. Lawn Bowls Club

How Bowls Roll

Bowls roll in a curve because they obey the laws of physics. How they are released cannot change this. Knowing the track they follow is very useful:

Where is the clear path to the jack?
Forehand or backhand?
What line gets into a group with weight?
Feeling confident?

This all comes with practice, and this track simulation can help with visualising the track. It is based on the following theory which predicts measurements that can be tested. Please feel free to prove it wrong on your green.

The short version

Bowls are slightly lop-sided so as they roll, they stay upright by turning towards the heavier side, they “precess”.

This alone would make them roll in a tight curve, but the centrifugal force caused by the turn has an effect in the opposite direction. As they slow down, the centrifugal force remains the same by tightening the turn.

The (really interesting) theory

The moment due to the centripetal acceleration has to remain equal to the bias (weight mg multplied by offset d). Otherwise, the path would change to make it equal.

If it did curve more:,

Centrifugal force would increase, making it curve less.

If it curved less,:

The bias wins and it curves more.

For a medium bias wood such as the Taylor Ace, this predicts:

The radius of curvature ('R" in metres) at any point is approximately equal to 8 times the speed squared (in metres per second)

We do not need the mass (m) - it cancels out, so a size 00 will behave the same as a 5.

g is 9.8 m/s/s

d is the bias caused by about 2 mm of melamine missing from one side of the bowl, which results in the centre of mass being just 0.7 mm from the running surface centre.

r is the radius of the bowl - size 3 is 55 mm

v is the velocity, which for a heavy green, could start at about 5 m/s, and slows to a stop as Kinetic Energy is converted by doing work against the rolling resistance with the green.

R is the radius of curvature of the track . This, together with the speed decreasing gives enough information to calculate the bowl's position throughout the shot.

Free precession does not happen. This is a bit like the terminal velocity of an object falling through air, where the air friction balances the weight, and acceleration does not happen.

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