Why does every 2d shape have a perimeter except for the circle and elipse which have a circumference, and would it be of benefit to standardise?
The circumference is the perimeter around a closed curve. A perimeter is the sum of the lengths of the edges of a closed figure.
I would say that because a circle/ellipse only has one edge, and “perimeter” generally implies “add the sides” in school mathematics, the term “circumference” could mean a continuous perimeter (with no corners).
I reckon that when students are asked for the “perimeter” of a shape they just add up the side lengths, but the “circumference” of a shape has a special formula.
Then when you get to doing perimeters of semicircles and such, then you’re mixing them so that to find the perimeter you use half the circumference, plus the straight bit, coz remember you add all the edges to get the perimeter. I think “circumference” is a useful word and it wouldn’t benefit anyone to standardise.
———————————————————————————————————–
Ambiguous Words
LENGTH – the longest extent of anything as measured from end to end. Can refer to shapes, time, clothing, as well as meaning long (”remarkable length”) and difficult (”he went to great lengths to get that”). However, I think that a questions such as “Find the length of the line AB” doesn’t bring that much difficulty.
BREADTH – refers to width, or side-to-side length, or sometimes ” the measure of the second largest dimension of a plane or solid figure”, or just size in general. Extremely confusing and ambiguous.
WIDTH – the extent from side to side, or breadth. It would appear that “width” means the same as “breadth”, but in a more precise and well used way. Students would probably be able to guess what the “width” of something was more easily than they could find the “breadth”. Put both these words on a test and heads will explode.
HEIGHT – the distance upward from a given level to a fixed point, the extent or distance upwards, or the distance between the highest and lowest points. Evidently if you have a shape and rotate it, its height will be different. How do you know which is supposed to be the height? The area of a triangle is half the base times the perpendicular height. In this case the height is in relation to the side you use as the base.
DEPTH – “a dimension taken through an object or body of material, usually downward from an upper surface, or from top to bottom of something regarded as one of several layers”. It also applies to seriousness, complexity, emotions, colour intensity, pitch, and an unfathomable space (the depths). I always think of depth as going into the page when shown a drawing of a 3D shape. It is clearly confusing.
THICK – the state or quality of being thick, or the measure of the smallest dimension of a solid figure. One of the more thought-provoking definitions: is it always the smallest dimension? Does it mean the same as width? Or breadth? If the smallest dimension is the height, is that the thickness too?
All these words have slightly different meanings but it could be possible for them all to be the same. It wouldn’t be that much of a stretch.
——————————————————————————————————
Number - 44 definitions, icluding:
Mathematics
- A member of the set of positive integers; one of a series of symbols of unique meaning in a fixed order that can be derived by counting.
- A member of any of the further sets of mathematical objects, such as negative integers and real numbers.
- A symbol or word used to represent a number.
- A numeral or a series of numerals used for reference or identification: his telephone number; the apartment number.
- A position in an ordered sequence that corresponds to one of the positive integers: the house that is number three from the corner; ranked number six in her class.
- One item in a group or series considered to be in numerical order: an old number of a magazine.
- A large quantity; a multitude: Numbers of people visited the fair.
Digit – any of the Arabic figures 1-9 and 0. Also any of the symbols of other number systems. Can also mean the breadth of a finger used as a unit of linear measurement.
Numeral - A word, letter, symbol or figure expressing a number.
Figure - A numerical symbol, and amount or value expressed in numbers, or a written symbol other than a letter. Plus 34 other non-mathematical meanings.
—————————————————————————————————–
Curve: A collection of points whose coordinates are continuous functions of a single independent variable.
Line: A collection of points whose coordinates are continuous functions of a single independent variable.
Straight line: A line traced by a point traveling in a constant direction; a line of zero curvature
Line segment: A portion of a line delimited by two end points; also, a line described by two sets of coordinates and the shortest path between them
————————————————————————————————-
Invariably
Not able to change, the same every time. Is this what we mean when we use it? Is this what students understand?