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Many people think that mirror images are images that are flipped top to bottom or left to right, but that is not the case. Dianna Cowern (Physics Girl) explains what mirrors do in the following video. So mirrors don’t flip length, vertical, or top to bottom (what Physics Girl calls “Y axis"), and mirrors don’t flip horizontal, width, or left to right (what Physics Girl calls “X axis”). Mirrors seemingly do the equivalent of flipping depth, or front to back (what Physics Girl calls “Z axis"). To understand this better look at a 3 second scene from the film Terminator-2: Judgement Day in the video below. The scene takes place at minute 1:12 when the old terminator model, T-800 (played by actor Arnold Schwarzenegger) slams the new terminator model T-1000 (played by actor Robert Patrick) against a wall. In this scene, the T-1000 terminator (which is made up of a “mimetic metal polyalloy”) flips itself front to back. His left hand becomes his right hand and vice versa, but his left hand is not flipped horizontally in the opposite direction to occupy the position previously occupied by his right hand. Mirrors do the equivalent of the effect portrayed in this scene. As Physics Girl explained in the video, when things appear to be flipped top to bottom or left to right by a mirror, it is us who are doing the flipping either by manipulating objects or by positioning ourselves or the mirror in the wrong direction. An example of this can be seen in the video below. This video was shot at the Rosenberg Palace (former Institute for noblewomen) in the Prague Castle complex in the city of Prague, Czech Republic. The room contains the Baroque Holy Trinity Chapel and the Chapel of the Immaculate Conception of the Virgin Mary. It seems that to ease the strain on the necks of visitors contemplating the superb art on the very tall ceiling, a mirror was installed on the floor. Alas, the mirror was installed at an angle facing the visitors that come through the door. As a result of this frame of reference, the image in the mirror appears flipped vertically with respect to the image on the ceiling. Some people looking at this would conclude that mirrors flip images vertically, but that is not the case. The correct positioning of the mirror should have been slanted in the direction of the man in the video standing behind the mirror. This would have maintained the image’s true orientation.
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The Municipal Library of Prague in the Czech Republic has an imposing cylindrical tower made up of 8,000 books that stretches from the floor to the ceiling. The tower is an art piece entitled “Idiom” by the Slovak artist Matej Kren. But even more remarkable is what you see when you peek through a 10 foot tear-shaped hole on the side of the tower.  Multiple Reflections This illusion is achieved by using two parallel mirrors: one in the floor and another in the ceiling. When a person walks in between parallel mirrors, the mirrors generate multiple images made up of reflections, reflections of reflections, and so on seemingly to infinity. However, some of the images will show the person looking forward and others will show the person looking backwards. In the case of the book tunnel, the surfaces reflecting on the mirrors are pretty much homogeneous, so the effect is created of a tunnel that stretches up and down to infinity! The picture is by the author and can be used with permission.
The response of the plant Mimosa pudica (also known as “Touch Me Not”) to mechanical stimulation has entertained countless generations. As you see in the video below, when the leaves of these plants are touched they fold, and even the branches drop in response to stimulation. This response may be a defense mechanism against insects or weather condition that may harm the plant in the open erect state. The interesting thing is that the reaction of the plant bears a similarity to the way our nervous system transmits signals. When the plant is touched, several receptors are activated in the leaf which causes a change in the distribution of charged atoms (ions) like potassium between the inside and outside of the cells of the plants. This change in the distribution of ions generates an electric signal called an action potential. In our neurons these actions potentials travel down the length of the neuron and communicate the signal to another neuron or to a muscle. In the plant these action potentials travel to the base of the leaf and into a structure called the pulvinus. The pulvinus is an area in the base of the leafs and the stems that is engorged with water, and the cells there are under considerable pressure (turgor). In mimosa, the engorged pulvinus is what keeps the leafs open and the stems erect. When the action potential arrives at the pulvinus, some chemical changes take place that causes it to rapidly lose water and therefore turgor. This sequence of events is what causes the leaf or stems of the mimosa to fold or drop in response to touch and other stimuli. In some cases, as you can see in the video, the folding of one leaf causes a chain reaction that causes other leafs to close. Mimosa is not the only plant that exhibits these rapid responses. The Venus fly trap also relies on a similar mechanism to close its traps. If two grenades fall near you, one on the ground and another in the water, what would you do? Would you dive in the water a certain distance away from the underwater grenade hoping that the water will shield you from the shrapnel, or would you dive to the ground hoping that not a lot of the shrapnel from the surface blast would hit you? Mark Rober teams up with Kevin (TheBackyardScientist) to figure this out. Their video is very good, so I will leave the explanation of the science up to them, but you can also check a written version here. |
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