By the board
Question: When skateboarders jump over an obstacle, I have watched carefully,
and the boarders do not lift the board by placing a foot under it. So how do
they lift the board? It鈥檚 very spectacular because sometimes they can leap over
jumps that are knee height.
Answer: Jumping the board into the air or onto and over obstacles is called
an ollie and forms the basis of a limitless array of tricks. To perform an ollie
the skater must be rolling forward with the back foot on the tail and the front
foot some way down the board. The skater crouches slightly then jumps upwards,
and as their weight leaves the board, the back foot flicks down, the tail hits
the ground and the whole board flips up into the air. The board rises to meet
the skater鈥檚 front foot and at the same time the front foot moves up the board,
pushing it back towards the horizontal and, as the back foot rises, bringing the
tail up from the ground and level with the front of the board. I鈥檝e seen skaters
ollie over shopping trolleys, tennis nets and picnic tables from a flat
surface.
Paul Brooks
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Milnathort, Kinross
Answer: Learning to make a skateboard ollie is very hard. With practice,
though, you can get far more than knee-high off the ground, and you can learn
tricks like spinning the board along its long horizontal axis (kick flipping).
If you stamp on the end of a stationary skateboard (pop it), it will jump into
the air, spinning back toward you.
The trick is to control the movement of the board with your feet. Put one
foot on the tail of the board and one in the middle. Stamp on the back of the
board, which forces the front up, and by dragging your front foot up you can
lift the board up with you, clearing the ground. Pushing your front foot down
straightens the board.
It is important that when you pop the board you immediately remove all your
weight by jumping, so you don鈥檛 hinder the height gained by the board.
In this way you can ollie a skateboard as high as you can jump from standing
still, but if you jump off a small ramp, it鈥檚 possible to ollie over cars, trees
and even houses.
Matt Venn
Leeds, West Yorkshire
Come off it Matt, the world record ollie leap is about 5 metres, set by
Danny Wainwright. If you wanted to clear a house you鈥檇
need an even bigger slope than the huge, half pipe that Wainwright used.
Weighty problem
Question: In 1938, while I was staying at a remote country house, I helped to
wind a suspended weight from the hall up into the roof space. As I recall, its
geared descent generated electricity which lit the sitting room throughout the
evening.
But according to my calculations, a 1-tonne weight descending from a height
of 10 metres would provide 30 watts of power for no more than 55 minutes.
Can my recollection be correct? And does anyone have any record of such a
device and how it works?
(continued)
Answer: Your request for any reader who owns a system of this kind to
contact you helped me to solve a problem of my own.
Some time ago I returned to my old home, long since demolished, and found the
remains of an Aerogen gas lighting system that illuminated the house from around
1918 until about 1936.
One of our evening chores was to go to the 鈥済as house鈥� to wind the pulley
which pulled the weight up a pole. On its gradual descent overnight, this weight
provided the pressure to drive gas through the system. The light was adequate
but it was not bright and the mantles often had to be replaced because of the
constant attention of moths and other night insects which died and blocked the
system.
I made enquiries through the Internet as to how this system operated, but
with little success. Then I saw your illustration of the system, which was
exactly the same as our Aerogen machine, and read how it worked
(The Last Word, 12 September).
Initially we used 鈥渂enzoline鈥�, which I have since discovered is
merely a crude form of petrol. The system also required that the drum be kept
full of water.
Geoff Sommerville
Wellington, New Zealand
This week鈥檚 question
In tune: While listening to the radio (on a sound system) tuned to 98.6 FM I
realised that the radio signal could be switched on and off as I moved to
different parts of the room.
It was so sensitive to my position that by sitting on a chair about 6 metres
from the radio it was possible to switch the sound on and off simply by leaning
forwards and backwards. What caused this phenomenon?
David Martin
Hamilton, New Zealand