Lawn Bowls in spring

From our upstairs Physics lab, we look out over a lawn bowls club and , now that spring has just about arrived, the lawn has been beautifully mown and the old folk who play have dusted off their white clothes and begun to play.

This led me to use the lawn bowl as a teaching tool for the girls/boys in y13.
Aside view of a lawn bowl is circular while the front on view shows their is more mass on one side. When a bowl stops it generally falls over and I asked them to explain this.
Kate :- " Where the bowl touches the ground is where the reaction force acts upwards. The gravity force acts through the centre of mass which is to the heavy side of the bowl, so there is a torque acting which is not balanced so it falls over."
( not only the best looking student with the shortest skirt, Kate is the brainiest).

We took some video of a bowl falling over and we were able to work out that it had a rotational velocity of 2.8 rad/s and Inertia of .00216 kg/m2.

Using Kinetic energy (rot.) = 1/2Iw2 , Kinetic energy (lin.) = 1/2 mv2 ( v = rw )

we got values of 8.5 mJ for rotational E and 21mJ for linear E and that the centre of mass of the bowl drops by about 2mm

When I asked them to explain why the bowl has a curved path when bowled, again Kate was to the fore. Distractingly shifting in her seat she declared; " the bowl wants to tip over in one directon so the friction force from the grass acts in the opposite way. When its travelling upright, this friction force is the only force acting on it, so shifts it to one side'.
When the bell goes for the end of class and the uncoil themselves from their seats, I sigh.

Next time I might get them to see that a bowl rocking on its side would do so with Simple Harmonic Motion.
Kapai

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Kiwiman

Author:Kiwiman
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