Physlink.com published answer: "My son William is doing a science fair project for 6th grade. He tried using different light bulbs to power a solar car. The incandescent bulbs (infrared, regular white and UVA) worked but fluorescent bulbs did not although they had the same light (lumens). He wanted to know why?"

 What a great topic for a science fair project!  To answer the question I want you to think about color.  Which colors have more intensity or are warmer to you? 

 

The nature of color is such that a material will absorb every frequency of color but the one it represents and that frequency will be reflected. Also consider lighter surfaces versus darker surfaces.  A pool deck is painted white to keep it cooler by reflecting all the colors of the spectrum.  A blacktop surface absorbs the energy from all frequencies of light reflecting very little and making it very hot.

 

Now back to the solar car science fair question.  Each of the lights mentioned in the problem had certain characteristics which were being judged for their effectiveness in powering a solar car.  While each light was distinct in spectrum, you need to consider not only which end of the spectrum you were dealing with, but how much or how wide of a spectrum you were dealing with.  Each of the bulbs that worked well with the car represented a wide spectrum of energy.  Even though the IR and UV bulbs are skewed to one end of the spectrum, you have to remember that there is electromagnetic (light) energies that go beyond the visible spectrum of light.  

 

A fluorescent light has a very narrow frequency band of energy.  You may have recognized this as objects look different in its light.  For years homeowners balked at the idea of putting fluorescent lighting in their homes even though fluorescent fixtures use a fourth the energy because it gives a cold look as opposed to the warm look of incandescents.  You may have also noticed fluorescent products such as artificial lighting for plants and aquariums that advertise fuller spectrum energy to enhance color, appearance and growth for these same reasons. You would expect these bulbs to not only give objects in its light better color, but since it is fuller spectrum, your solar car should perform better.

 

There is also higher photonic energy on the infrared side of the spectrum because of its longer wavelength.  If you were to consider all options that light has when striking a solar panel:  It can reflect off of it and not create electricity; it can be absorbed and not create electricity; it can be absorbed and create electricity; and it can pass straight through and do nothing.  The nature of longer wavelength IR light is such that it is more easily absorbed.  On the other hand UV light is higher frequency light and has the tendency to pass through objects rather than be absorbed.  One might expect, depending on the purity of the light source, that the IR bulb did better than the UV bulb.  Additionally, fluorescent bulbs usually tend to be found in the UV side of the light spectrum and so these UV characteristics would apply.

Physlink.com published answer: "What is a fuel-cell and how does it work?"

Perhaps the simplest way to describe the process a fuel cell uses to produce electricity is to compare it to reverse electrolysis. Everyone is familiar with the classic experiment of electrolysis, where direct current is conducted to an anode and a cathode submerged in a liquid high in electrolytes (free ions as from salts for example). The effect is that the electrical energy separates the hydrogen and oxygen with the atoms of oxygen collecting at the anode and the atoms of hydrogen collecting at the cathode.

In a fuel cell, the process is somewhat reversed. Gaseous hydrogen and oxygen flow separately around either side of two electrolytic plates serving as anodes and cathodes. These are separated by a thin polymer membrane which serves as a filter. As free hydrogen and oxygen atoms collect on the plates, they are chemically attracted to each other, but the polymer membrane prevents all but the small hydrogen protons from passing through. The potential created by shearing off the hydrogen proton from its electron is usable electricity and is carried around the membrane in an external circuit. The byproducts of the fuel cell are heat (from the proton electron separation), and water.

It sounds like the greatest thing since sliced bread except there are present limitations: A single fuel cell produces just a fraction of a volt, so many fuel cells must be stacked together to produce the desired amount of electricity; The output of the fuel cell is directly proportional to the purity of the hydrogen. Since it requires more energy to extract pure hydrogen than is produced by the fuel cell, they are impractical as an energy source for most applications; Alternative hydrogen fuel sources for fuel cells, such as methanol, natural gas, or petroleum as more efficient when burned in traditional electrical production methods; Finally, the membrane filter is very expensive because it is platinum covered. The platinum coating acts as a catalyst to induce the disassociation of the hydrogen protons from their electrons to facilitate the electrical potential.

Answered by: Stephen Portz, M.Ed, Technology Teacher, Space Coast Middle School

https://www.physlink.com/education/askexperts/ae376.cfm

Physlink.com published answer: "What are the advantages of ABS braking systems compared to other hydraulic braking systems?"

The advantages of ABS brakes (anti-lock braking system), are just as the meaning of their acronym implies, they eliminate or greatly reduce the possibility of brake lock up and therefore provide a better chance of steering out of trouble.

Conventional hydraulic brakes work by using a cylinder (actuator), which squeezes brake calipers together around the wheel's rotor when the brake petal is depressed. Difficulties arise with these conventional brakes if the road is slick and the driver executes a panic stop. Under these conditions the wheels may lock up and the tires run the risk of losing their grip. When tires lose their grip of the road, there is a good chance that the car may go into an uncontrolled spin. This is why drivers in older vehicles have been taught in the past to pump brakes when on icy roads.

ABS brakes were designed to combat the problem of tire lock up and uncontrolled spins. Since brakes are most effective at slowing the car at a point just before wheel lock up, a system that provides for wheel braking while preventing wheel lock up is very desirable.

Anti-lock brakes do just this by using a computer processor to monitor and control the application of the brakes. At braking, the processor monitors rpm and braking pressure on each of the vehicle's wheels. With this information, measured amounts of pressure are sent to each wheel in the form of hydraulic pulses of pressure to the calipers. These pulses achieve the desired braking pressure without allowing the wheels to lock up.

Answered by: Stephen Portz, Technology Teacher, Space Coast Middle School, FL

Physlink.com published answer: "Is it purely coincidental that the moon rotates on its axis in synch with its revolution around the Earth, keeping the same face always pointed toward us?"

The Earth's moon rotates (spins on its axis), every 27.32166 Earth days. It revolves around the Earth in the exact same period - every 27.32166 Earth days. Because of the synchronization of revolutionary and rotational periods, the same portion of the moon's surface is always directed toward the Earth.

The phenomena of which you speak is not coincidental, and 'universally' speaking, throughout the galaxy, may well be considered more typical of planet moon relationships than perhaps an anomaly.

It is fairly well understood how the gravitational interaction of the moon with our Earth is responsible for the tides on our planet. But far less recognized and understood is the gravitational effects of the Earth on the moon. The mass and speed of rotation of the Earth influence the moon in that some of its rotational energy is actually transferred to the moon. The result of this being that the moon rotation is slowed while also being placed continually into a higher orbit and thus slowing its revolution. The net effect of this gravitational relationship is that the moon's rotation has been slowed to match its orbital period. Ironically, since the Earth is giving up some of its rotational energy to the moon, the Earth and moon will, in the far distant future, reach a synchronization of rotational periods, as Pluto and its nearer to its mass moon Charon have already done.

Many of the moons in the solar system have also reached this point of equilibrium. In Jupiter, the moons Amalthea, Thebe, Io, Ganymede, Callista, and Europa, all have identical rotational and revolutionary periods.

Answered by: Stephen Portz, Technology Teacher, Space Coast Middle School, FL

Physlink.com published answer: "Einstein believed in determinism but the quantum theory disbanded this idea. Do you believe that determinism will be revitalized by the unified field theory? Why or why not?"

 Surprisingly enough the questions that you pose are as much philosophical as they are scientific.  And I am positive that you also understand that these questions can not be answered with what we presently understand about quantum mechanics, unless of course we have discovered our own little unified theory, but it can make for an interesting discussion, so here goes…

 

The statement that you make about quantum theory “disbanding” Einstein’s ideas about determinism is somewhat troubling – since neither quantum point of contention determinance or indeterminance, has been indisputably validated.  So we can’t say that one necessarily trumps another. But, what I think I hear you saying when you mention the unified theory revitalizing thoughts about determinism is that you hold a belief that Einstein will eventually be vindicated for maintaining his determinant position on quantum characteristics.

 

It should be remembered that Einstein largely broke with the great minds of his day as he maintained that "GOD does not play with dice."  The essence of his statement was to say that just because we do not presently have the ability to measure and determine quantum behavior, does not mean that quantum behavior is indeterminate. 

 

These beliefs ran contrary to many of the scientists at the time such as Heisenburg, Schrodinger, and Bohr, who based their belief system of quanta mechanics with theories supporting indetermination.  These scientists and others combined to form what was called the Copenhagen Interpretation of thoughts on quantum behavior which was the largely accepted theory of the time, and in many ways is still maintained today.

 

Heisenburg of course, is famous for the Uncertainty Principle, which states that the simple act of measuring quanta requires an intrusion into its miniscule realm, which in itself invalidates the measurement through the added energy of “looking.”  Schrodinger’s Cat explains determining quantum characteristics in much the same way but with a much more entertaining visual.  A cat locked in a box with a glass vial full of poison gas which will break upon the random decay of some unknown radioactive material.  How would you know if the cat in the box had died or remained yet alive.  You don’t!  You can only know if you open the box and look, but in the act of looking will you accelerate or cause the radioactive decay?  In this way, Schrodinger maintained, the cat can be said to be both dead and alive.  

 

It should be noted that Stephen Hawking’s feelings about these ideas were such that he said that every time he heard the Shrodinger’s Cat explanation for quantum mechanics he wanted to reach for his gun and shoot someone.

 

The basis for stating that your original question is as much philosophical as it is scientific is that it represents a great hold out in the scientific community in the random nature vs order and intelligent design debate.  For some scientists the notion of random patterns of chance as it deals with indeterminism in quanta, is an ontological debate, not just an epistemological debate.  In others words, people feel that we are not just talking about a simple scientific fact, we are dealing with the very fabric of the cosmos and how everything is that is.  One side saying ahh-haa, the universe has random order and can’t be described with an equation. The other side postulating, at least in part, that order would indicate an intelligent design in that all things have a mathematical component or description.

 

It would be naive not to characterize the role that philosophy plays in this specific question as a distinct movement within the scientific community.  Scientific minds in the time of Einstein were desperately looking for breaks from the metaphysical world, or that which was difficult to explain without scientific methods. Describing quantum characteristics in terms of the randomness of nature (indetermination), had a really good secular look and feel about it and was embraced, notwithstanding the criticisms of Einstein, and later, Hawking.  For these reasons, uncertainty as it deals with quantum mechanics is still widely held.   This is not to say that all the proponents of determinism espouse the concept of intelligent design, it is just that they believe that all things may be described mathematically, which definitely hints of order in the universe.  Eventually, when we have the ability to look unintrusively and measure to the degree of sensitivity required to define quanta, they believe it will be revealed that all particles follow an orderly pattern which may be determined with an equation.

 

The suggestion that you make about a unified theory resurrecting determinism may yet prove to be true.  It does seem a little ironic that scientists are looking for the Holy Grail in a unified theory that explains how everything in the universe operates while still espousing the belief that quantum mechanics are indeteminant.

Physlink.com published answer: "Who is the inventor of television?"

 Who is the inventor of television? You have really opened up a can of worms with that question! Probably no other invention in history has been so hotly disputed as the prestigious claim to the invention of 'Tele-vision or 'long-distance sight' by wireless.'

Since Marconi's invention of wireless telegraphy in 1897, the imagination of many inventors have been sparked with the notion of sending images as well as sound, wirelessly. The first documented notion of sending components of pictures over a series of multiple circuits is credited to George Carey. Another inventor, W. E. Sawyer, suggested the possibility of sending an image over a single wire by rapidly scanning parts of the picture in succession.

On December 2, 1922, in Sorbonne, France, Edwin Belin, an Englishman, who held the patent for the transmission of photographs by wire as well as fiber optics and radar, demonstrated a mechanical scanning device that was an early precursor to modern television. Belin's machine took flashes of light and directed them at a selenium element connected to an electronic device that produced sound waves. These sound waves could be received in another location and remodulated into flashes of light on a mirror.

Up until this point, the concept behind television was established, but it wasn't until electronic scanning of imagery (the breaking up of images into tiny points of light for transmission over radio waves), was invented, that modern television received its start. But here is where the controversy really heats up.

The credit as to who was the inventor of modern television really comes down to two different people in two different places both working on the same problem at about the same time: Vladimir Kosma Zworykin, a Russian-born American inventor working for Westinghouse, and Philo Taylor Farnsworth, a privately backed farm boy from the state of Utah.

'Zworykin had a patent, but Farnsworth had a picture''

Zworykin is usually credited as being the father of modern television. This was because the patent for the heart of the TV, the electron scanning tube, was first applied for by Zworykin in 1923, under the name of an iconoscope. The iconoscope was an electronic image scanner - essentially a primitive television camera. Farnsworth was the first of the two inventors to successfully demonstrate the transmission of television signals, which he did on September 7, 1927, using a scanning tube of his own design. Farnsworth received a patent for his electron scanning tube in 1930. Zworykin was not able to duplicate Farnsworth's achievements until 1934 and his patent for a scanning tube was not issued until 1938. The truth of the matter is this, that while Zworykin applied for the patent for his iconoscope in 1923, the invention was not functional until some years later and all earlier efforts were of such poor quality that Westinghouse officials ordered him to work on something 'more useful.'

Another player of the times was John Logie Baird, a Scottish engineer and entrepreneur who 'achieved his first transmissions of simple face shapes in 1924 using mechanical television. On March 25, 1925, Baird held his first public demonstration of 'television' at the London department store Selfridges on Oxford Street in London. In this demonstration, he had not yet obtained adequate half-tones in the moving pictures, and only silhouettes were visible.' - MZTV

In the late thirties, when RCA and Zworykin, who was now working for RCA, tried to claim rights to the essence of television, it became evident that Farnsworth held the priority patent in the technology. The president of RCA sought to control television the same way that they controlled radio and vowed that, 'RCA earns royalties, it does not pay them,' and a 50 million dollar legal battle subsequently ensued.

In the height of the legal battle for patent priority, Farnsworth's high school science teacher was subpoenaed and traveled to Washington to testify that as a 14 year old, Farnsworth had shared his ideas of his television scanning tube with his teacher.

With patent priority status ruled in favor of Farnsworth, RCA for the first time in its history, began paying royalties for television in 1939.

Philo Farnsworth was recently named one of TIME Magazine's 100 Greatest Scientists and Thinkers of the 20th Century.

References:

• The United States Patent Office patent interference #64,027
• The Pioneers of Electronic and Mechanical Television
  by MZTV
• The Birth of Television
  by the VideoUniversity.com
• Who invented television?
  by Paul Schatzkin
• On John Logie Baird
  by Jones Telecommunications & Multimedia Encyclopedia

Answered by: Stephen Portz, Technology Teacher, Space Coast Middle School, FL

https://www.physlink.com/education/askexperts/ae408.cfm

Physlink.com published answer: "How does a cat land on its legs when dropped?"

 Cats have the seemingly unique ability to orient themselves in a fall allowing them to avoid many injuries. This ability is attributed to two significant feline characteristics: A 'righting reflex' and a unique skeletal structure.

The 'righting reflex' is the cat's ability to first, know up from down, and then the innate nature to rotate in mid air to orient the body so its feet face downward. Animal experts say that this instinct is observable in kittens as young as three to four weeks, and is fully developed by the age of seven weeks.

A cat's 'righting reflex' is augmented by an unusually flexible backbone and the absence of a collarbone in the skeleton. Combined, these factors allow for amazing flexibility and upper body rotation. By turning the head and forefeet, the rest of the body naturally follows and cat is able reorient itself.

Reports of cats surviving falls of several stories in height have coined the expression of cats having 'high rise syndrome.' Like many small animals, cats are said to have a non-fatal terminal falling velocity. That is, because of their very low body volume-to-weight ratio these animals are able to slow their decent by spreading out ' flying squirrel style. Simply put, animals with these characteristics are fluffy and have a high drag coefficient giving them a greater chance of surviving these falls.

Answered by: Stephen Portz, Technology Teacher, Space Coast Middle School, FL

https://www.physlink.com/education/askexperts/ae411.cfm

Physlink.com published answer: "Why does a golf ball slice or draw? What is the difference in the flight of a golf ball hit with back-spin and one hit with top-spin?"

 No less than four principles are used to explain the movement of objects such as golf balls as they travel through the air. Since air is considered a fluid, then fluid dynamics, or the characteristics of moving fluids or objects moving through them are described using a Reynold's number. This relationship is part of the research done by British physicist Osborn Reynolds for which it is appropriately named, and is a function of the viscosity of the air, the speed of the air and the size and shape of the object moving through the air.

A characteristic of air as an object passes through it is such that it is best described by using a layers model. These layers, particularly the boundary layer around the object itself is a critical determining factor as to how the object will behave through the fluid. Since the boundary layer adjacent to the ball is most subject to friction from the surface of the ball, the smoothness of the surface obviously plays a part. A rougher surface causes air to 'grip' the ball for a longer period of time before passing, creating turbulence and a thickened boundary layer. A smoother surface will allow the air to flow easier over the ball creating what is called laminar flow. Unfortunately, laminar flow, while initially having less drag, is also prone to separation, which produces an increased drag. By inducing turbulence in the boundary layer through the use of dimples in a golf ball, or seams on a baseball, greater layer adhesion is realized, and surprisingly enough, a decrease in overall drag as compared with smooth surfaces.  

That said, now on to the focus of your question: What causes a golf ball or any projectile for that matter, gravity excepted, to deviate from its initial trajectory? That was basically the same question that a German engineer, G. Magnus, was asking himself when studying cannon ballistics. He noted that a cannon with a barrel bent to the left actually made the cannon ball curve to the right. Further research revealed to him that the barrel bent to the left imparted a clockwise spin on the ball. This discovery led to an entire field of study explaining the behavior of rotating objects as they travel through the air.


'Golf ball with backspin [rotating CW] with air stream going from left to right. Note that the air stream is deflected downward with a downward force. The reaction force on the ball is upward. This gives the longer hang time and hence distance carried.' - from Lift and Air Resistance by Tom Steiger, Department of Physics, University of Washington.

Simply put, this is what his research found: A rotating ball traveling through the air will create relatively low pressure, explained in Bernoulli's principle, on the side of the ball rotating the same direction as the air stream (faster air speed). High pressure will occur on the side of the ball rotating against the flow of air (slower air speed). Higher pressure (side rotating against the air stream), will induce premature laminar separation around the ball. Lower pressure air (side rotating with the air stream), has better adherence to the ball and deflects the air stream toward the area vacated by the high pressure separation, creating a 'wake.'

It is very much like turning the tiller on a boat to deflect the wake on the boat and alter its course. Turn the tiller to deflect water to the left boat causes the rear of the boat to move right. Deflect the water to the right, and rear of the boat turns left.

Since the golf terms of slice and draw are particular to the left or right-handedness of the golfer, we will simply use left or right to describe the deflection of the ball. If an imperfect hit on the golf ball causes the ball to spin clockwise, the ball will deflect air left causing the ball to curve to the right. If the hit imparts a counterclockwise spin, the ball will deflect air to the right causing a curve to the left. Top-spin, deflects air upward forcing the ball downward; while backspin will cause the ball to rise above its normal gravity determined parabolic arc.

The amount the ball will deviate from its initial trajectory is a function of the density of the air, the velocity of the ball, and the rpm of the spin on the ball.

The description of these principles is aptly named the Magnus Effect.

References:

• Why do dimples on a golf ball allow it to travel farther?
• Aerodynamics of Cricket Balls
• Fluid Dynamics of Sports
• Lift and Air Resistance

Answered by: Stephen Portz, Technology Teacher, Space Coast Middle School, FL

Physlink.com published answer: "How do Transistors Work?"

Transistors are composed of three parts ' a base, a collector, and an emitter. The base is the gate controller device for the larger electrical supply. The collector is the larger electrical supply, and the emitter is the outlet for that supply. By sending varying levels of current from the base, the amount of current flowing through the gate from the collector may be regulated. In this way, a very small amount of current may be used to control a large amount of current, as in an amplifier. The same process is used to create the binary code for the digital processors but in this case a voltage threshold of five volts is needed to open the collector gate. In this way, the transistor is being used as a switch with a binary function: five volts ' ON, less than five volts ' OFF.

Semi-conductive materials are what make the transistor possible. Most people are familiar with electrically conductive and non-conductive materials. Metals are typically thought of as being conductive. Materials such as wood, plastics, glass and ceramics are non-conductive, or insulators. In the late 1940's a team of scientists working at Bell Labs in New Jersey, discovered how to take certain types of crystals and use them as electronic control devices by exploiting their semi-conductive properties.  

Most non-metallic crystalline structures would typically be considered insulators. But by forcing crystals of germanium or silicon to grow with impurities such as boron or phosphorus, the crystals gain entirely different electrical conductive properties. By sandwiching this material between two conductive plates (the emitter and the collector), a transistor is made. By applying current to the semi-conductive material (base), electrons gather until an effectual conduit is formed allowing electricity to pass The scientists that were responsible for the invention of the transistor were John Bardeen, Walter Brattain, and William Shockley. Their Patent was called: 'Three Electrode Circuit Element Utilizing Semiconductive Materials.'

Reference:

• Who invented the transistor?
• How do transistors work?

Answered by: Stephen Portz, Technology Teacher, Space Coast Middle School, FL

https://www.physlink.com/education/askexperts/ae430.cfm

Physlink.com published answer: "How does a solar cell work? Is it possible to create one using simple lab apparatus?"

Solar cells (photovoltaics), use the energy from light photons to create electrical potential between two layers of silicon crystal. The atomic nature of silicon, with some added impurities, is what makes it all possible. The outer orbital electron shell of a silicon atom contains four electrons. Since it takes eight electrons to fill the electron shell, a silicon atom is continually looking for four electrons to bond with. This it finds by bonding covalently with other atoms of silicon forming a characteristic crystalline structure. Silicon atoms thusly joined are very stable and are not electrically conductive, but this is where the impurities come in. By 'doping' the silicon with substances such as phosphorus and boron, entirely different electrical properties are introduced into the silicon creating semi-conductive material.

For instance, when phosphorus joins with silicon, it creates an N-type semi-conductive material because phosphorus has five electrons in its outer shell. The silicon wants four of them but that leaves one electron hanging out by its lonesome and giving the molecule a negative charge. If boron joins with silicon, it creates P-type semi-conductive material (positive charge), as boron has three electrons in its outer shell. Even though silicon bonds with it, it leaves an electron 'hole,' where the molecule is positively charged and is still seeking an electron.

If layers of phosphorus impregnated silicon and boron-impregnated silicon are joined together with metal leads or conduits, an electrical potential can be created with some help from light. When light photons strike the phosphorus layer containing the extra electrons, those electrons can be sheered off and freed. When they are, they immediately recognize the potential in the boron layer and head that way. If a load (some work that you want to have done with electricity), happens to be connected in between these two layers where the potential has been created, then the migrating electrons are useful electrical current.

Solar cells are a wonderful alternative energy sources but have definite limitations. Since not all visible light is useful for this process, most of the sunlight energy can not be used to free electrons in the solar cells. Much of it is reflected or passes through not hitting the desired electron target. In addition, the electrical potential is very small and even with the most efficient solar cells; they must be chained together in large arrays to produce enough electricity to be useful. Because of the nature in which they produce their electricity, solar cells do experience a slight drop in effectiveness but they essentially never wear out. Then of course the most obvious problem: what do you do if the sun is not shining?

The nature work of the required to fabricate semi-conductive materials is probably beyond the realm of simple lab equipment. But many solar cell companies will give away broken cell fragments for the asking if you are looking for something to play with.

Also, if you are an educator, contact the Florida Solar Energy Center.

References:

• How Solar Cells Work by NoOutage.com
• Bond and Molecular Polarity by Brenda Wojciechowski and Paul Cerpovicz (Georgia Southern University)

http://www.nooutage.com/howsolar.htm http://www2.gasou.edu/chemdept/general/molecule/polar.htm
Answered by: Stephen Portz, Technology Teacher, Space Coast Middle School, FL

Physlink published answer: "Does the temperature of a football (or baseball, soccer ball, etc) affect how far it will travel when kicked/hit?"

Temperature can affect a couple of different variables in a ball to alter the distance it will travel from an impact. For inflated balls, the temperature can change the air pressure inside the ball giving an over inflated effect if it was warmed, or and under inflated effect if it was cold. (Have you ever tried dribbling a basketball without enough air in it?) The amount of air pressure then is directly proportional to the temperature of the air inside.

For solid core balls, like baseballs, golf balls etc' temperature has a similar effect on the ball but the mechanics are a bit different. Here, the characteristics of the material inside the ball are responsible for the bounciness of the ball.

A ball's bounciness is dependent on the elasticity of its constructed materials. The property of elasticity allows the ball to retain kinetic energy during a collision by having the ability to flex without breaking and then return to its original shape. This measure of a material's elasticity is called its coefficient of restitution.

An object with a low coefficient of restitution will lose a great deal of its kinetic energy in a collision through breaking or deforming, or through the generation of sound or heat. Compare the kinetic energy transmission through steel balls suspended on strings as they bounce back and forth in an example of a high coefficient of restitution. Now consider a lump of clay or a piece of glass in a collision, both materials having very low restitutional values ' they simply do not transfer energy well because they are not as elastic.

How does all this tie back into the temperature of materials? Temperature can also affect elasticity ' the colder a material gets, the less elastic it can be. Under cold conditions, the material can actually become more of an 'energy sink' ' absorbing energy rather than transferring it.

Both inflated and solid core balls rely on the principle of coefficient of restitution. A warmed, (over inflated) ball is more elastic than a cold, (under inflated) ball just as a solid core ball that is warm has more elasticity than an identical ball that is cold.

Answered by: Stephen Portz, Technology Teacher, Space Coast Middle School, FL

https://www.physlink.com/education/askexperts/ae469.cfm

Physlink.com published answer: "How does a sailboat move upwind?"

Since the early days of sailing, ships have undergone a continuous improvement in design so that today's modern sailboats, at casual glance, may give the appearance of having the ability to travel upwind (against the wind). In actuality, a sailboat can not travel directly into the wind but employs sailing technique known a 'tacking,' to zigzag across a headwind.

The shape of the sail and the hull of the boat are the major factors that have allowed sailboats to more closely approach the ability of sailing upwind. In the early years of sailing ships, the European ships had a square sail design. This design only allowed for sailing with a favorable wind ('before the wind, or wind on the quarter'). With trade expanding into the East, Europeans were exposed to triangular sails in use on small boats in the orient. It was observed that these triangular sails allowed for navigation using a half wind (wind at 90 degrees to the boat), which further increased the ship's maneuvering ability ' particularly in port, where ships previously were 'dead in the water' without a favorable wind. European vessels incorporated the triangular sails fore and aft of the mainsails for the purpose of navigating out to sea to catch the favorable trade winds for the square sails to utilize.

The use of triangular sails caught on as the sail shape of choice as other benefits to the design were realized. By using a triangular sail design and centerboard (overdeveloped keel), it was possible to travel against the wind using a technique known as tacking.

Tacking allows the boat to travel forward with a wind at right angles to the boat. The boat travels for a time at an angle toward its desired course (to the right for instance), then the captain swings the boom of the sail and tacts back across the desired course at an angle to the left in a zig-zag fashion. In this way, tacking allows the boat to use prevailing wind from many other angles than in earlier sailing methods.

Since the boat is dependent on the wind for propulsion, the strength of the wind and the area of the sail used to catch the wind obviously play a part ' but how does a wind at right angles to the boat allow the boat to move forward?

This is accomplished with a bit of vector mathematics. The wind is the large force vector in the equation. As the wind pushes at approximate right angles to the boat, the boat's large keel (underwater wing shaped centerboard), poses a very large drag force against the boat being pushed in the direction of the wind. Since the keel is aligned with the length of the boat, the boat really wants to travel forward, and the resultant thrust vector is in that direction.

The shape of the sail also provides forward thrust. As the triangular sail inflates with a wind it creates an airfoil shape. As subsequent wind passes around the sail (airfoil), negative pressure is induced out front of and on the leeward side of the sail. This in turn causes surrounding air to rush into the sail and propel the boat further. This sail/airfoil action is compounded, as the boat travels faster, the wind around the sail creates more negative pressure, causing the boat to travel faster causing more negative pressure and so forth.

Answered by: Stephen Portz, Technology Teacher, Space Coast Middle School, FL

https://www.physlink.com/education/askexperts/ae438.cfm