Sound is a transverse wave made by particles banging into one another. (thus sound cannot travel in a vacuum)
In air (a gas), the particles are a long way apart so it takes longer for them to collide with one another to carry the sound.
In a solid, say a bar of metal, all the particles are jammed really close together, so if you bang one end of the bar, the wave will travel quickly down the length of the bar.
Sound travels at around 330m/s in air, and how fast it goes in solids depends on the properties of the solid, but I think for most metals it is very roughly around 600m/s
Hope this helps.
They improved them a lot! If your question would be more specific, it would be easier to answer. The tennis balls used to be wads of hair or wool wrapped in stuff, but now they are more rubbery for bounce. I don't know exactly how.
Most hurricane deaths are from drowning. Storm surge is what kills most people in a hurricane. The storm pushes water to the shore and causes a wave of 5 to 25 feet which inindates the shore and the inland. Tornadoes are an aftermath of the storm.
4D refers to a coordinate system made of 4 axes, all at right angles from each other.
In common use 4D generally refers to coordinates in 3D Space/Time. 3 of these coordinates are in space. The fourth is the position in time, where time is considered mathematically as a fourth axis that is at right angles to all other axes. 3D space/time geometry is at the heart Einstein's equations of physics.
4 Space, or four dimensional space is like 3D space/time except that the fourth dimension is not considered to be position in time but rather a fourth spatial coordinate that is along an axis at right angles to all other axes. So called "hyper-cubes" and "hyper-spheres" are 4 space equivalents of spheres and cubes. The easiest way to understand 4-space is to think first off about 2-space, or 2D objects. A circle is a 2D object. A sphere is the extension of a circle into the 3rd dimension to make a 3D object. A hyper-sphere is the extension of that Sphere into the fourth dimension to make a 4D object. A 4D hyper sphere has the same relation to a normal 3D sphere as that sphere has to a 2D circle. Note that the term "4D" is also misused in all sorts of marketing jargon to mean other things. The scientific term for this usage is "nonsense."4d is like when you go see a movie you feel it like in sea world a movie was in 4d and water splashed me in the face