Top perch on a church
QUESTION Why are church steeples topped with golden cockerels? WHILE many early weather vanes — used to show the wind direction — were in the shape of flags, banners or pennants, the weathercock became a popular symbol of Christian iconography.
In the sixth century, Pope Gregory I called the cockerel the most suitable emblem of Christianity.
During Pope Leo IV’s reign (847-855), a cockerel was mounted on the top of the Old St Peter’s Basilica in Rome.
Later that century, Pope Nicholas I issued a decree that all churches should have a cockerel on their dome or spire to serve as a reminder of Jesus’s prophecy of St Peter’s betrayal on the day of the Last Supper: ‘Before the rooster crows you will deny me three times (Luke 22:34).
The cockerel is also a symbol of the rising sun so, ‘like Christ, it announces the arrival of the day after the night, the arrival of good after bad’.
The oldest known weathercock is the Gallo di Ramperto. It has been on display in the Museo di Santa Giulia in Brescia, Italy, since 1891, after having greeted the dawn on the steeple of a local church for more than 1,000 years. Amelia Hughes, Beaumaris, Anglesey. QUESTION In the TV series The Last Ship, the captain orders a full stop by reversing the engines. Everyone is thrown forward, as though in a car making an emergency stop. Would this happen? THE answer lies in Newton’s first law of motion: every object will remain at rest or in uniform motion in a straight line, unless compelled to change its state by the action of an external force.
If a ship is in forward motion and is suddenly stopped, the people onboard the ship will continue to move forward. This effect is seen more often in cars and trains when emergency braking is applied and the passengers lurch forward.
In a car, this could result in the passengers being thrown through the windscreen if they weren’t held in place by their seatbelts.
However, ships don’t stop suddenly. If the thrust of the propellers is reversed, it takes time for them to stop turning and then even longer for them to start turning in reverse and apply a force sufficient to stop the ship.
The fastest way to stop a ship is to reverse the thrust of the propellers while changing the direction of the ship by turning it, increasing the resistance of the ship though the water. This is known as a crash stop.
But it will still take several minutes for the ship to come to a stop and the rate at which it decelerates would not be enough to cause the crew to lurch forward, as depicted in the TV series The Last Ship.
The only time that would happen is if the ship were to hit a solid object, such as a rock, an iceberg or another ship. It is estimated that a fully laden supertanker takes 20 minutes to come to a stop from cruising speed. Even smaller ships require several minutes, not seconds, to stop.
In practice, ships will rarely execute emergency braking because it increases the wear on the expensive engines.
Speedboats and cabin cruisers are able to stop much more quickly because they don’t exert so much inertia — the tendency to keep still or keep moving in the same direction, in accordance with Newton’s law.
Passengers or crew might be thrown forward if a speedboat were to undergo an emergency stop.
Bob Cubitt, Northampton.
QUESTION We wrongly say that the sun goes up or down. What other scientifically incorrect expressions do we use?
FURTHER to the earlier answer, Egyptian archaeology TV programmes tend to have presenters going down the Nile to the Valley of the Kings.
They may be going down the map, but they are travelling upriver.
Meanwhile, there are book titles referring to plants and trees, suggesting the authors don’t know that trees are plants.
The title should be herbs and trees because, botanically, herb means a nonwoody plant. However, in cuisine, it refers to a plant grown for flavouring.
R. J. Andrews, Farnborough, Hants.
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