Questions without answers #9

Why do airplanes offer life jackets rather than parachutes?

When a plane crashes down onto the ground there is no need for either life jacket or parachutes because in all probability you’ll be dead. When a plane crashes into the water or has to ditch having life jackets on board makes much more sense than having parachutes. Life jackets are easy to use and, once you’re in the water the vest will keep your head above the surface. This way it can even save unconscious people. Wearing a life jacket also lengthens the time before hypothermia sets in because of keeping you afloat and thus saving your energy.
Using a parachute is far more complicated. First and foremost there would be chaos. If a plane is crashing down everyone would want to jump out first. There’d be accidents in the air when people crash into each other. Additionally, it takes a certain height to be able to jump and open your parachute. While a plane is losing height quickly, some people might not have that time. Another problem is that most people don’t know how to steer a parachute.
All in all, parachutes are no good compared to life jackets even concerning plane crashes.
And why need a parachute? When a plane crashes you’re always sure to come down.

If a “Black Box” is indestructible, why aren’t planes build from this material?

Black boxes or more accurately flight recorders help to investigate airplane incidents or accidents. To preserves black boxes they have to be build to a certain standard. Normally, a black box can stand temperatures up to 1000 °C and impacts of up to 3400 g (1 g = 9.81 m/s²) and they’re waterproof until at least 6000 meters. Through an underwater locator beacon (ULB) a black box can be located underwater.
The two most common types of flight recorders are flight data recorders (FDR) and cockpit voice recorders (CVR) often combined as a single FDR/CVR unit.
A black box can be found either in the middle or in the tail of an airplane as those parts will most likely to “survive” a crash.
The interesting thing is that the box itself and its inner life might or will be destroyed in a crash. Only the so called crash-survivable memory units (CSMU) are protected by three layers of materials and, it seems, indestructible. The memory cards are encased by an aluminum housing protected by high-temperature insulation which is made of dry-silica and 2.54 cm thick. The outer case is made of stainless steel and 0.64 cm thick. It can also be made of Titanium.
If planes consisted completely of steel they’d simply be too heavy and thus they would need too much fuel. And planes that are constructed completely of aluminum wouldn’t be stable enough. So, various materials are needed to build planes.

Why does someone ask questions although he does not want to get an answer?

In that case it’s important to know why someone asked the question in the first place. If the person is expressing an opinion or conveying his point of view he may ask a rhetorical question at the end of his speech emphasizing what he just said. Rhetorical questions require no answer as they don’t serve the purpose of gaining information.
On the other hand people might not want to hear the answer to a question because they already know it. Or maybe they are afraid of the answer but had to ask the question for reasons of peace of mind. So, there are many reasons one might ask a question but not want to know the answer.

How do “Keep off the grass”-signs get onto the grass?

If such a sign is found at the edge of the grass whoever put it there did not have to step on the grass. However, if they are placed in the middle of the grass somebody had the right to put it there. Additionally, as long as there is no sign asking you to keep off the grass, you are allowed to step on it. And as soon as you put the sign in place you leave the grass and so are obeying what the sign dictates. See, no harm done.