## Tuesday, March 4, 2014

### Daily Physics News 03/04/2014

Posted from Diigo. The rest of my favorite links are here.

## Saturday, March 1, 2014

### The Physics of Skiing

 Image from: uk.eurosport.yahoo.com Credit: Reuters
I was watching TV last night about skiing in The Sochi 2014 Winter Olympics (just try Sochi in Google) and I found myself thinking the Physics behind it.
It was evident that we have energy transformation (from potential to kinetics):
"As the skier begins the descent down the hill, potential energy is lost and kinetic energy (i.e., energy of motion) is gained. As the skier loses height (and thus loses potential energy), she gains speed (and thus gains kinetic energy). Once the skier reaches the bottom of the hill, her height reaches a value of 0 meters, indicating a total depletion of her potential energy. At this point, her speed and kinetic energy have reached a maximum. This energy state is maintained until the skier meets a section of unpacked snow and skids to a stop under the force of friction. The friction force, sometimes known as a dissipative force, does work upon the skier in order to decrease her total mechanical energy. Thus, as the force of friction acts over an increasing distance, the quantity of work increases and the mechanical energy of the skier is gradually dissipated. Ultimately, the skier runs out of energy and comes to a rest position. Work done by an external force (friction) has served to change the total mechanical energy of the skier." (in Physics Classroom)

I found that all the materials must be design to support bumps and torsion:
"Ski materials have received an equally extensive makeover. Engineers are continually working to make skis lighter and more flexible to absorb bumps in the snow, while keeping them rigid enough to hold their shape during turns. For that reason, metal skis were introduced in the 1950s. Today’s skis, because of their broader tips and tails, have to endure torsional forces that skis of the past could not have withstood. Most skis are now made of sandwiches of fiberglass, wood, aluminum alloys, glue, and polymers." (in Discover Magazine)
They running with a crouch position to reduce drag force:
"A skier maximizes his speed by minimizing resistance to motion, both from air resistance and snow resistance. A skier minimizes his air resistance (drag) by reducing his projected frontal area. He does this by going into a crouch position, which (along with improving his ability to hold balance) results in a lower drag force, which acts in a direction opposite his velocity, slowing him down. The picture below shows a downhill skier in a crouch position." (in Real World Physics Problems)
And they have curved skies to prevent slipping on snow:

"To prevent slipping, the angle ψ must be greater than or equal to 90° . This means that the component of FR parallel to the plane of the ski, will either be zero (for ψ = 90°), or it will point directly into the snow, towards the right (for ψ > 90°), and the "wall" of snow will prevent it from slipping." (in Real World Physics Problems)

What a great sport!

## Wednesday, February 26, 2014

### Balance

 Credit: wiki.brown.edu

Center of Gravity if an interesting concept that children can explore at home and classroom.
Check the video:

More:
Balance & Center of Gravity
http://www.algarcia.org/AnimationPhysics/BalanceTutorial.pdf
http://web.mit.edu/jabbott/www/physicsofbalance.html
Equilibrium & Torque
http://www.physicsclassroom.com/class/vectors/u3l3c
http://hyperphysics.phy-astr.gsu.edu/hbase/torq.html

## Tuesday, February 18, 2014

### Daily Physics News 02/18/2014

Posted from Diigo. The rest of my favorite links are here.

## Saturday, February 15, 2014

### Galileo's Birthday

Today we celebrate Galileo's birthday (14 February 1564).

His contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the discovery of the four largest satellites of Jupiter, and the observation and analysis of sunspots.

Galileo made original contributions to the science of motion by showing a remarkably modern appreciation for the proper relationship between mathematics, theoretical physics, and experimental physics.
A biography by Galileo's pupil Vincenzo Viviani stated that Galileo had dropped balls of the same material, but different masses, from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass.Galileo proposed that a falling body would fall with a uniform acceleration, as long as the resistance of the medium through which it was falling remained negligible, or in the limiting case of its falling through a vacuum. He also derived the correct kinematical law for the distance travelled during a uniform acceleration starting from rest—namely, that it is proportional to the square of the elapsed time ( d ∝ t 2 ). Prior to Galileo, Nicole Oresme, in the 14th century, had derived the times-squared law for uniformly accelerated change, and Domingo de Soto had suggested in the 16th century that bodies falling through a homogeneous medium would be uniformly accelerated. Galileo expressed the time-squared law using geometrical constructions and mathematically precise words, adhering to the standards of the day. (It remained for others to re-express the law in algebraic terms).
He also concluded that objects retain their velocity unless a force—often friction—acts upon them, refuting the generally accepted Aristotelian hypothesis that objects "naturally" slow down and stop unless a force acts upon them. Galileo was the first to express it mathematically, verify it experimentally, and introduce the idea of frictional force, the key breakthrough in validating the concept. Galileo's Principle of Inertia stated: "A body moving on a level surface will continue in the same direction at constant speed unless disturbed." This principle was incorporated into Newton's laws of motion (first law). (adapted from Wikipedia)
http://galileoandeinstein.physics.virginia.edu/lectures/gal_accn96.htm
http://csep10.phys.utk.edu/astr161/lect/history/galileo.html

## Thursday, February 13, 2014

### A step forward to fusion energy

 Fusion reactions happens in Sun's core.Image credit: wikipedia
The ignition is an essential part to make possible a viable alternative source of energy, but has not yet been reached. An important step on the way to the ignition is having the energy generated by fusion reactions, confined to a plasma, exceeds the amount of energy stored in the deuterium-tritium fuel and during the implosion, resulting in a gain of energy. In the article published in Nature, scientists at LAWRENCE LIVERMORE NATIONAL LABORATORY revealed that they acquired energy gains by manipulating the laser to reduce instability in the implosion.
Scientific paper: NATURE

## Saturday, February 8, 2014

### Daily Physics News 02/08/2014

Posted from Diigo. The rest of my favorite links are here.