Shapes

An arch is a curved, self-supporting shape usually used over doorways or to support old bridges. Arches shift the downwards force at the top of the arch to a sideways force at the bottom of the arch, so there must be a strong wall holding the base of the arch up. Arches work particularly well underground where the earth holds the sideways force. When two arches are put next to each other, the sideways forces are cancelled out, so a row of arches together e.g. under a long bridge only need thin walls or pillars holding the arches up.

The stone at the top center of an arch is usually a slightly different shape, or is more decorative. It is called the keystone.

An arrow is a projectile that is fired from a bow. Arrows have a pointed end that is used to pierce things.

An arrow is also any shape that looks like the arrow projectile. Arrows are used to point somewhere, or tell you which direction to go.

A blob is like a globule. It is something with no particular shape, used to describe a lump of something soft and squishy or something you can't quite make out, for example "at this distance, Harry was just a blob".

Used as a verb, you bump into something when you hit it, but not especially hard. You might bump your knee on your coffee table if you are walking around your living room in the dark.

As a noun, a bump is a raised, slightly rounded area on something else. The stone pillar in the picture has a lot of bumps carved into it.

A circle is a shape with one long, curved edge that is the same size in all directions. Things that are like a circle are often called round. The circle in this picture is a pot, with a cat asleep in it.

A coil is a word used to describe something that is in loops on top of each other to form a helix or loops around each other to form a spiral.

The photo is of a fire hose coiled into a spiral.

A surface is concave if it curves inwards, forming a hollow. The coin slot in the picture is concave.

A cone is a shape with a round bottom that gets smaller as it goes until it reaches a point. If you cut a slice through a cone parallel to the bottom, it will be the same shape as the bottom. If you cut a slice through the cone vertically going through the top point, you will get a triangle.

A surface is convex if it curves outwards, forming a mound. Mirrors are often made convex so that they offer a larger field of view.

A crescent is a shape that is part of a circle, but wider in the center and narrowing to a point at the ends. As the moon wanes it becomes a crescent.