There are two types of spin that a player can apply to a tennis ball, those being topspin and backspin. What prompted my thoughts on this idea would be my attendance of the University of Rochester tennis match today against Nazareth. As these advanced players made the ball skip and flip and kick every which way, my mind went crazy! :labmate)
A topspin shot is hit by sliding the racquet up and over the ball as it is struck. By dragging the racquet over the ball, the friction between the racquet's strings and the ball is used to make the ball spin forward, towards the opponent. The shot dips down following impact with the court and also bounces at a lower angle than would a shot with no spin applied to it. As a ball travels towards a player after bouncing, it has natural topspin that is caused by the friction of the tennis court. When hitting a topspin shot, the player is reversing the spin of the ball, which requires more energy. This change in energy from potential to rotational kinetic energy allows the player to effectively execute the top spin shot.
A backspin shot is hit in the opposite manner, by sliding the racquet underneath the ball as it is struck. This causes the ball to spin towards the player who just hit it as it travels away. What is very interesting about the back spin shot and has been proven by physicists all over the world is that hitting this shot requires only roughly about half of the raquet speed of a top spin shot, for to execute this shot the player does not change the rotation of the ball. The oncoming ball bounces off the court with topspin, spinning from top to bottom as it comes toward the player. When a player returns the ball with a slice shot the direction in which the ball spins around the axis of rotation is maintained. From the players perspective, it actually seems as if the ball is moving away from them.
Many common materials like wood, water, plants, animals, diamonds, fingers etc. are considered not to be magnetic but are in fact very slightly diamagnetic. Diamagnets repel, and are repelled by a strong magnetic field, and two of the strongest known diamagnetic materials are bismuth and graphite. Compared to the forces created by traditional magnets, diamagnetic forces are exponentially weak, however when arranged and prepared properly, can produce startling effects, levitation in this case. UCLA university has done multiple studies and found the most efficient and effective configurations for showing levitation in action.
In the first configuration here we can see what seems to be a small golden cylinder floating in between two fingers. However in reality the magnet is levitated by a vertical superconducting solenoid electromagnet at a point at which the magnet is rendered vertically stable and however unstable in the horizontal plane. Thus, the floating magnet wants to move off sideways, but is however, for this reason is lined with bismuth and therefore repels the magnet overcoming the horizontal instability and the result is stable levitation.
Another configuration is shown below. In this one, the magnet is suspended at a point far below the electromagnet where in this case it is vertically unstable and stable on the horizontal plane, unlike the example above. Diamagnetic plates are placed above and below to stabilize vertically. In the case above, human fingers were used as the diamagnetic plates to accomplish for real what magicians claim to do while only producing an illusion.
Alright, this blog is for all you pyros out there. I couldn't help but want to delve a little deeper into the nature of fire, and what I found is pretty interesting. In actuality, fire is simply a gas thats hot enough to incandesce, which means give off blackbody radiation whos color is determined by the temperature. Very hot fires can on occasion even reach the plasma phase, where they become partially ionized. However, the average fire burns at about 1000F, which produces the characteristic red-orange flame that we all recognize. When burning objects, one can notice that they burn at different rates or perhaps colors. This is because the electron structure of some materials and compounds absorb the energy, exciting the electrons to a higher energy level and emitting different photons. A perfect example of this is sodium, which gives off a distinctive yellow color. In addition the surface area must be considered. For example, paper burns much faster than wood for this reason, for surface area gives the substance ready access to oxygen. Hydrocarbons are another thing that burns incredibly well, however this is for a much different reason. They give off more energy than cellulose, which produces the normal 1000F temperature, actually because they lack oxygen, so when supplied with it the reaction is much more drastic.
While we use percent error to dictate how far we off in class, there are far more efficient ways of defining the error of the set. Standard deviation, for example, given a value, will give rise to numbers that fall within one S.D., two S.D. and so on.
"One can find the standard deviation of an entire population in cases (such as standardized testing) where every member of a population is sampled. In cases where that cannot be done, the standard deviation σ is estimated by examining a random sample taken from the population. An estimator for σ used when sample size is very large is the standard deviation of the sample, denoted by sN and defined as follows:"
This method is effective for creating intervals for which certain points would have to lie within and give us the ability to decide on percent error for an entire group of values. The closer the value of S.D. approaches 0, the less the error percent is.
Population concerns on Earth are leading scientists to inquire whether colonizing Mars is possible. As of now, over 78,000 people have applied to leave Earth forever and live on Mars. Mars One, a nonprofit organization, is sponsoring the colonization with a take-off date sometime in 2023. Out of the applicant pool, four will be chosen to send first to Mars. The first four will lay the groundwork for a permanent colony. Two years after the first four land, Mars One would send up more people to the colony. With the application process underway, it seems as though scientists have discovered ways for humans to survive on Mars indefinitely. However, this is not the case. Many, many concerns exist such as how will the colonists feed themselves? Will crops which grow on the Earth also grow on Mars?
The first settlers of Mars will most likely be farmers. Yes, they will be astronauts; but, if survival is of any importance to them, they will learn to farm in order to eat. Research which has been conducted supports the idea that growing crops is possible in microgravity. However, those working for NASA do not know to what extent the gravity of Mars will effect crop growth. Also, Mars' surface only receives about half of the sunlight that the Earth's surface receives. Will plants be able to grow with limited sunlight? On top of the already limited sunlight, pressurized greenhouses would be necessary to grow crops. The greenhouses would block out more light. So, additional light would be necessary from other sources than the sun. What would power additional light sources? How would that power be generated and sustained?
Radiation would also be a problem faced by those on Mars. Mars does not have as strong of an atmosphere as the Earth. More radiation reaches the surface of Mars than the surface of the Earth. Inhabitants would need a way to reflect the radiation or shield themselves from the rays.
To live on Mars, man must master the art of agriculture in microgravity. Feeding the inhabitants of Mars is one among many more necessary tasks of survival. As of now, research is still being conducted. The 78,000 who have already showed interest in living on Mars are a bit stupid or extremely bold. With current technology man would not survive on Mars. I do not doubt though that technology will develop in the near future for man to successfully live on Mars.
