Knowledge N Fact4u

Why is plastic not used in home construction ? •Plastic materials are used in several ways in home construction. Plastic has useful properties such as water resistance, corrosion resistance, electrical insulation, and durability. •Here we are using the common meaning of the word "plastic": a synthetic moldable solid. Among the uses of plastic in home construction are: •Sewage pipes. These are increasingly being made out of plastic such as PVC instead of metal because PVC is cheap, corrosive resistant, light, and somewhat flexible. •Water supply lines. These are increasingly being made out of plastic such as PEX because PEX is cheap, strong, and flexible. The relatively high flexibility of PEX leads to better water flow and quicker installation. •Fuel supply lines. •Electrical conduits. These are channels that carry various electrical wires. •Insulating coating on electrical wires. •Housewarp. This is the weather barrier that is placed just behind the...

Why are stars not blurred even though the earth is moving ? •Stars are blurred when viewed from earth. We just don't notice it much with our naked eyes because of the high temporal and low spatial resolution of the human visual system. •Take a glow stick, sparkler, or flashlight and spin it very quickly in the dark. You don't see an individual object anymore, but see instead a circular blur of light. •The reason for this is that the spin rate is faster than the rate at which our eyes can discern distinct images.  •The distinct images of the object get smeared together in a process known as motion blur.  •So why don't the stars look like spinning glow sticks? The rotation of the earth does cause the stars to spin in the sky, but the spinning is much slower. •Whereas it takes the stars one day to trace out a circular path in the sky, it takes tenths of a second for the glow stick to spin in a circle.  •Our eyes can mostly keep up with the motion of the stars becau...

Why do car tires protect you from lightning strikes ? •Car tires do not protect you from lightning strikes. Although the rubber in a tire acts as an insulator at low voltages, the voltage in a lighting bolt is far too high to be stopped by tires or air.  •No matter how thick your tires are, they don't stop lightning, according to scientists. •A study states that inside a car can be a safe place to wait out a lighting storm, but it's not because any materials are blocking the lightning. •Rather, if the car is struck by lightning, its metal frame redirects the electrical current around the sides of the car and into the ground without touching the interior contents.  •The ability of a hollow conducting object to protect its interior from electrical fields and currents is one of the fundamental principles of electromagnetics.  •Such an object is called a Faraday cage. For this reason, riding around in a convertible, on a motorbike or on a bicycle duri...

How do tractor beams work ? •Up until recently, tractor beams (beams of light that tow objects) existed only in the world of science fiction. •While large-scale tractor beams that can tow space ships are still machines of the future, microscopic tractor beams are here today.  •The idea at first seams to defy physics. Shoot light at an object and the light's momentum should push the object away from the light source according to the law of conservation of momentum; not pull it closer like a tractor dragging its cargo. •But what if you managed to create a situation where upon striking the object, the light gains forward momentum instead of losing it.  •In that case, the law of conservation of momentum tells us that the object will lose momentum in the forward direction, even to the point of going backwards, towards the light source. •So there is a way to make a tractor beam without violating any physics, if you can get the light to ga...

Why is lead used in pencils even though lead is poisonous ? •The core of a pencil does not contain lead and never has. Pencils contain a form of solid carbon known as graphite.  •According to a study, the graphite pencil was first developed and popularized in the 1600's.  •The first users of graphite simply dug this mineral out of the hills and discovered it could be sawed into sticks and used as an excellent writing tool.  •During the 1600's, no one knew the chemical nature of this material, as chemistry itself was still in its infancy. •Since this writing material behaved similar to metallic lead, but had a darker color, people began calling it "black lead".  •Eventually, the name of the core of the pencil got shortened to "lead". In 1779, German chemist K. W. Scheele finally determined pencil lead to be composed of pure carbon.  •A decade later, A. G. Werner decided that this carbon material needed a new name and proposed the name "graphi...

Why don't dark-skinned people get sunburns ? •Dark-skinned people do get sunburns. While it's true that the higher pigment levels that make certain people's skin look dark helps protect against sunlight, the pigments do not block 100% of the light. •The skin pigment melanin is produced by special skin cells called melanocytes to protect the body from the damaging effects of ultraviolet light.  •Higher levels of melanin means less sunburn and less skin cancer. •But even the darkest-skinned person is not protected 100% from sunlight. •A study found that 13% of black women and 9% of black men reported getting at least one sunburn in the past year.  •Furthermore, 38% of Hispanic women and 32% of Hispanic men reported getting at least one sunburn in the past year.  •For comparison purposes, the average value across all ethnicities and genders was 50.1%. While dark-skinned people definitely get fewer sunburns, they still get them.  •When a dark-skinned person g...

Why does chocolate cause acne ? •Chocolate does not cause acne. Acne is caused by overactive sebaceous glands.  •Sebaceous glands are microscopic glands connected to the hair follicles.  •Their job is to secrete skin oil (sebum), which travels up the shaft of the hair and out onto the skin in order to waterproof the body.  •If the glands secrete too much skin oil, the channel along the hair's shaft becomes clogged.  •As a result, a buildup of skin oil and dead cells occurs in the glands and the hair follicle.  •This stagnant, clogged mass just below the skin's surface becomes infected with bacteria and turns into a pimple.  •Sebaceous glands accelerate their secretions in response to high levels of sex hormones, such as present during puberty.  •The causes of acne are therefore: 1) elevated sex hormones, 2) sebaceous glands that are overly sensitive to sex hormones, and 3) the presence of bacteria that take advan...