(Mathhombre) Miscellanea

Handshakes

Warm up sketch inspired by the naked-geometry.

On geogebratube for you to play. Has a tool to make multiple copies of your own.

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loversdreamersandyou posted a still from this bit this morning and I reblogged it on geekhombre. Turns out it’s from a pretty sophisticated math bit. AND it’s the last skit Jim Henson and Frank Oz did together on Sesame Street.

spring-of-mathematics:

Type of Spirals: A spiral is a curve in the plane or in the space, which runs around a centre in a special way.
Different spirals follow. Most of them are produced by formulas:The radius r(t) and the angle t are proportional for the simplest spiral, the spiral of Archimedes. Therefore the equation is:
(3) Polar equation: r(t) = at [a is constant].
From this follows
(2) Parameter form:  x(t) = at cos(t), y(t) = at sin(t),
(1) Central equation:  x²+y² = a²[arc tan (y/x)]².

You can make a  spiral by two motions of a point: There is a uniform motion in a fixed direction and a motion in a circle with constant speed. Both motions start at the same point. 
(1) The uniform motion on the left moves a point to the right. - There are nine snapshots.
(2) The motion with a constant angular velocity moves the point on a spiral at the same time. - There is a point every 8th turn.
(3) A spiral as a curve comes, if you draw the point at every turn(Image).

Figure 1: (1) Archimedean spiral - (2) Equiangular Spiral (Logarithmic Spiral, Bernoulli’s Spiral).
Figure 2 : (1) Clothoide (Cornu Spiral) - (2) Golden spiral (Fibonacci number).

More Spirals: If you replace the term r(t)=at of the Archimedean spiral by other terms, you get a number of new spirals. There are six spirals, which you can describe with the functions f(x)=x^a [a=2,1/2,-1/2,-1] and  f(x)=exp(x), f(x)=ln(x). You distinguish two groups depending on how the parameter t grows from 0.

Figure 4:  If the absolute modulus of a function r(t) is increasing, the spirals run from inside to outside and go above all limits. The spiral 1 is called parabolic spiral or Fermat’s spiral.
Figure 5: If the absolute modulus of a function r(t) is decreasing, the spirals run from outside to inside. They generally run to the centre, but they don’t reach it. There is a pole.  Spiral 2 is called the Lituus (crooked staff).

Figure 7: Spirals Made of Line Segments.

Source:  Spirals by Jürgen Köller.

See more on Wikipedia:  SpiralArchimedean spiralCornu spiralFermat’s spiralHyperbolic spiralLituus, Logarithmic spiral
Fibonacci spiral, Golden spiral, Rhumb line, Ulam spiral
Hermann Heights Monument, Hermannsdenkmal.

Image: I shared at Spirals by Jürgen Köller - Ferns by Margaret Oomen & Ferns by Rocky.

Spiral compulsion. But this is a handy reference.

nakedgeometry:

∞ the 1st ever naked geometry piece, 2003! ∞ tumblr ∞ facebook ∞ etsy ∞

I might call this the handshake spiral.

nakedgeometry:

∞ the 1st ever naked geometry piece, 2003! ∞ tumblrfacebooketsy

I might call this the handshake spiral.

Can’t believe this was the Bizarro cartoon for today. Off to Twitter Math Camp!

Can’t believe this was the Bizarro cartoon for today. Off to Twitter Math Camp!

p5art:

A real Treasure Trove! :) From total beginner to more advanced.

Wow! Simon Gregg got playing with the same 20-80-80 triangle as I did, but his results are a lot prettier! Read the post. Wonder at the marvels.

Wow! Simon Gregg got playing with the same 20-80-80 triangle as I did, but his results are a lot prettier! Read the post. Wonder at the marvels.

David Marain (@dmarain) shared an angle chasing puzzle in the 80-80-20 isosceles triangle. Quite a nice one.

I chased a bit, then modeled in GeoGebra. Then I made a tool for making an ASA triangle which was handy for making angle chasing problems. Then I generalized the problem, and found that the 80-80-20 triangle had lots of neat situations that other triangles do not. (Here it is on GGBTube)

Is there something that makes this triangle special?

P.S. Turns out Simon Gregg (@Simon_Gregg) was also intrigued by this, and made some great mathart along the way. Check out his post.

geometricloci:

Opere di Eugenio Carmi.
Opere esposte a Spoleto (PG) Italy.
http://www.spoletoarte.it/art_Eugenio_Carmi.php
 (10 foto)

wonderful.

visualizingmath:

mathani:

Two curves cut all circles at right angles: straight line and a tractrix.

I didn’t know what a tractrix was, so I Googled it! Tractrix definition from Wikipedia: Tractrix (from the Latin verb trahere ”pull, drag”; plural: tractrices) is the curve along which an object moves, under the influence of friction, when pulled on a horizontal plane by a line segment attached to a tractor (pulling) point that moves at a right angle to the initial line between the object and the puller at an infinitesimal speed. 
Here’s a gif from Wikipedia showing a tractrix being created from dragging a pole:

visualizingmath:

mathani:

Two curves cut all circles at right angles: straight line and a tractrix.

I didn’t know what a tractrix was, so I Googled it! Tractrix definition from Wikipedia: Tractrix (from the Latin verb trahere ”pull, drag”; plural: tractrices) is the curve along which an object moves, under the influence of friction, when pulled on a horizontal plane by a line segment attached to a tractor (pulling) point that moves at a right angle to the initial line between the object and the puller at an infinitesimal speed

Here’s a gif from Wikipedia showing a tractrix being created from dragging a pole: