Naked Science Forum
General Science => General Science => Topic started by: DERRINALPHIL on 11/03/2007 22:11:50
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I am a cricket umpire in Australia and we have to place stumps in the ground. If you hit a stump in you damage the top of the stump and the bails then tend to fall off all the time.
Some umpires use a rubber mallet rather than a hard hammer to do the job BUT I reckon all using a rubber mallet does is that you have to hit them more times and the damage to the top of the stump would be identical to using a metal hammer.
It seems to me that you have to apply the same amount of force/momentum to push the stump in and some of the force is lost with the deformation of the rubber mallet. Then there is the issue of the hardness/resistance of the wooden stump to deformation.
I think this is interesting but no other ump does.
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Hi DERRINALPHIL,
WELCOME......
well..as you so very well know...us here in the UK don't know how to play cricket !..but what about if you you used a piece of wood that covers all three stumps together and then hit down on that with the mallet/hammer to hit the three in at the same time...........do you think that might help ?
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Hi DERRINALPHIL,
WELCOME......
well..as you so very well know...us here in the UK don't know how to play cricket !..but what about if you you used a piece of wood that covers all three stumps together and then hit down on that with the mallet/hammer to hit the three in at the same time...........do you think that might help ?
possibly with three notches cut out, so you do not damage the shape of the stumps.
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Dear Moderator,
The problem remains with your solution as you are spreading the force over three stumps. You will still have to hit them with at least the same force as required to knock them in individually. Probably more as you may hit them, as a unit, off centre and waste energy spreading them sideways.
The other solution could work. I am a dentist so I will make an accurate impression of the top of a stump and them cast a metal device that will sit over the top of the stump. We can then bash away till the cows come home(or England win the ashes again)
But my question remains unanswered.
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Hitting something with a hammer is surprisingly more complex than you would think. For the sam collision (same weight hammer moving at the same speed) the amount of impulse (force x time is the same) but this can be applied as a very high force for a short period of time or a low force for a much longer period of time.
Because a rubber mallet is softer the collision will be spread out over a longer period and therefore do less damage, but apply a smaller force. Also because the mallet deforms the impact is spread over a larger area of stump, so reducing the force per unit area (pressure) even more, and it will be the pressure that actually damages the wood fibres.
So all well and good, obviously the rubber mallet is best then - it would be in relatively soft ground where the amount of motion is related to how hard you hit it, then yes.
The problem comes when you want to knock it into hard ground, to do this you have do essentially damage the ground, so you need very high peak forces, which the rubber mallet won't do, and you could be there for a month and wouldn't get anywhere, which will probably do more damage to the stump as you say.
In this case you want to get the advantage of the rubber which spreads the impact over most of the top of the stump and the steel hammer which will give you nice high forces.
Ideally what you would want is a steel/metal/hardwood cap shaped like the top of the stump which you could place over the stump then hit with a hammer, this would spread the force out over the whole of the top of the stump, whilst not absorbing the high maximum forces.
[diagram=174_0]
Although i don't know how practical this would be to make.
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In hard ground you could make a pilot hole (or a set of three pilot holes)by hammering in (then removing) a metal spike(s)to make the hole. This should make it possible to hammer in the stumps without damaging them.
If you did want to hammer in the stumps you could find a method of gripping the side of the stump (rather than the top) and transfering the hammer energy through the side rather than the top. This would reduce the pressure on the wood.