Science

Five main groups of uses can be identified:
1. Building and decorative stone: Stone used for its resistance to weather or its aesthetic appeal walls and decorative purposes. Buildings, walls and paving slabs.
2. Aggregates: Stone used for its strong physical properties and sorted into various sizes for use in concrete, coated with bitumen to make asphalt or used dry as bulk fill in construction. Mostly used in roads, concrete and building products.
3. Industrial purposes: Limestone can be used for its chemical properties as calcium carbonate (CaCO3) in farming and manufacturing industry.
4. Lime burning (calcining): Limestone when heated to a high temperature breaks down into lime (calcium oxide) and carbon dioxide gas. It can then be used as a more powerful alkali than limestone or used as a cement with sand, to make mortar, or as a soil improver in agriculture.
5. Cement: If limestone is mixed with clay or sandstone before firing, it can produce Portland cement, which when mixed with aggregate makes concrete.

Shadows are formed because light travels in straight lines. I should point out that this is a simplified view as demonstrated by diffraction where light does bend around sharp corners. Also, in order for light to travel in a straight line, it has to travel in vacuum or a homogeneous/even medium. The light will bend, as it does when the medium changes and light enters at the non-right angle. Or when the medium is uneven, like air close to ground on a hot day. Then there is gravity. According to General Theory of Relatively, mass warps space-time and thus light will travel in a "curved" line. From the question, I am guessing that the person who asked the question is young and/or has not read a lot about physics yet. Shadows are formed when light encounters an object which it cannot pass through and thus get blocked. Because the light became blocked, the area behind it will be in darkness, which we call a shadow. Another person has already pointed out that for shadows to form, two things are needed viz. A light source and an object to block the light. I want to add that we need a third viz. A screen, for most of what we usually call a shadow; although this is not required as far as physics/optics is concerned. Only when we see the absence of light falling on the screen do we call it a shadow.

They are left over from the formation of stars and planets billions of years ago. Before zipping around the Sun with their characteristic big tails, comets that we see in our solar system start out as big chunks of rock and ice just floating around in something called the Oort Cloud. When the gravity from a large passing body, like a star, becomes strong enough, some large chunks of ice get pulled away from the cloud and head toward the Sun. As that ball of ice gets close enough to the Sun, its heat begins to melt some of the ice that makes up the comet. The melted ice becomes a gaseous tail that extends away from the source of the heat (in this case, the Sun). The tail is pushed out by the Sun's solar wind. What keeps the comet in motion and guides its path is the gravity from all the planets and stars it passes. When a comet is in our solar system, most of the gravity affecting the comet's motion is due to the Sun. As a comet gets closer to the Sun it moves faster and faster, because the closer an object is to the Sun the stronger the Sun's gravity acts on it. As well as moving faster near the Sun, the comet's tail will grow in length since more of the ice will be evaporating.