Skiing: It’s All About Friction

glide2It’s all about friction. Really. Friction from the snow, friction from the air, friction from the surface of the ski or the clothing you wear.  The physics of skiing is all about how to overcome drag and resistance and allow a skier to slice his/her way down the mountain.  And if Newton’s laws have anything to do with it, a skier who controls friction best has the best chance of winning.

Find out the basics of friction and skiing.

Articles by Marcia Howell

Skiing: It’s All About Friction (Basic)

glide3aWhen Bioengineer, Parker Tyler, goes skiing, she probably isn’t thinking about the biology or the physics behind the activity.  Rather, he is enjoying the crisp, cool, mountain air, the clear view of the slope, and the anticipated exhilaration he will feel as she maneuvers to the bottom. She likely doesn’t consider earth’s gravitational force (9.81 m/s), or potential energy, or kinetic energy, or her own mass, or any of those other factors that will contribute to his acceleration.  However, scientists do think about these things and their thinking has affected many facets of the industry from clothing to equipment to style.

It’s all about friction. Really. Friction from the snow, friction from the air, friction from the surface of the ski or the clothing you wear.  The physics of skiing is all about how to overcome drag and resistance and allow a skier to slice his/her way down the mountain.  And if Newton’s laws have anything to do with it, a skier who controls friction best has the best chance of winning.

Back to Parker, her potential energy is greatest at the top of the hill where she perches until the start of her run.  Her body is physically fit and adrenaline is taking over, sending added energy to her muscles, vision center, quick decision making regions of the brain, and the area that controls coordination.  Once she leaves starting position, gravity pushes down, mass pushes down, but the acceleration down the slope kicks in and changes how the forces affect the ride.  Potential energy turns into kinetic energy, or energy of motion, and everything he touches tries to resist and slow the movement.

Since Parker is a wise skier, she wears a GS suit (a sleek, form fitting suit with a minimum of abrasive surface area) and aerodynamic boots, hat (or helmet), gloves, etc.  As she accelerates, she assumes a crouching position to reduce air resistance and tighten the air current close to her body.  His skis are designed specifically for the type of skiing being done, the edges are sharp, and the bottoms are carefully waxed.  The wax waterproofs the skis, prevents them from drying out, and it reduces the wet drag of a kind of “suction” type friction from the snow.

When Parker comes to a curve, the skis will either be eased into the turn with the ski pointed in the same direction as her velocity, making a sharp cut in its wake, or she will choose a skidding type of maneuver where the skis will be forced in the direction she wishes to go, leaning away from the curve at a 45-90 degree optimal angle, and literally plowing snow away from her. Some skis have special designs that scientists have found will decrease the drag and increase the speed these curves can be safely made.  Surely, Parker will have researched and purchased those that fit his style and goals for skiing.

By the time she reaches the bottom, her potential energy is expended, the ensuing kinetic energy is maxed out, and now friction works against him to slow down her acceleration to a stop.  His adrenalin will return to normal levels, and her blood circulation and other systems will begin to function normally once again.  (At least until the next run.)

Research will continue to change the sport of skiing.  And no doubt, the savvy skier will keep tabs on the newest and best ways scientists will come up with to help us beat the forces working against us.

By: Marcia Howell, University of Utah

References:

Energy Transformation for Downhill Skiing. 2012. Retrieved from http://www.physicsclassroom.com/mmedia/energy/se.cfm

The Physics of Skiing. Real World Physics Problems. 2009. Retrieved from http://www.real-world-physics-problems.com/physics-of-skiing.html

Locke, B. 2012. The physics of skiing. Retrieved from http://ffden2.phys.uaf.edu/211_fall2002.web.dir/brandon_locke/Webpage/homepage.htm

Mears, A. 2002. Physics of Alpine Skiing. Retrieved from http://www.suberic.net/~avon/mxphysics/anne/Annie%20Mears.htm

Materials Science: Wood vs. Aluminum Bats (Basic)

It is common knowledge that metal baseball bats perform better in competition than wooden bats. The question is…why? There are several factors that explain why metal and wooden bats have such a disparity in performance.

In a 1977 study (when aluminum bats were first beginning to show up on the scene) using college players taking batting practice, it was shown that line drives coming off the wooden bat registered at 88.6 miles per hour while the aluminum bat registered batted ball speeds upwards of 92.5 miles per hour. This may not seem like a huge difference but it is large enough to, in some cases, take a pop fly and turn it into a home run.

The first reason metal bats outperform their wooden counterparts is that they are hollow. The hollow nature of metal bats allow them to be swung at a faster speed even if they are the same weight as a wooden bat. This is because the center of mass of the metal bat is closer to the handle and this allows a hitter to control more of bat’s mass and bring it through the hitting zone at a faster speed. This higher bat speed will produce faster batted ball speeds and send the ball farther.

With the center of mass closer to the handle, the bat has a lower moment of inertia. Inertia is the tendency of an object to resist motion. It is a function of mass and the square of a distance. With the center of mass closer to the handle, a hitter has to put in less work to moving the bat and swing at a higher speed.

When a ball is struck by a solid wood bat, the ball is compressed up to 75% of its diameter. A lot of energy goes in to this deformation and this will take away from the energy the ball will have when it leaves the bat. The hollow metal bat acts sort of like a spring and more of the energy from the hitter is able to be transferred into the ball and send it farther.

Finally, metal bats do not break! When a wooden bat shatters, up to 80% of its energy can be lost. Batted balls rarely travel far when a bat is broken in a swing. This obviously does not occur in metal bats because of the strength of the material. This is also much cheaper for baseball teams as the need a small number of aluminum bats compared to the hundreds gone through by teams with wooden bats.

A study conducted that tested distances based on batted ball speeds using metal and wooden bats showed drastic results. Each ball was angled at 35 degrees and the batted ball speed was measured. A ball hit at 98.8 mph with a wooden bat will travel around 388 feet. A ball hit at a speed of 101.5 mph with a metal bat will travel just over 400 feet and a ball hit it a whopping 106.5 mph with a metal bat will travel upwards of 425 feet. This test shows that one of the major factors in the distance a ball travels is bat speed and higher bat speeds can be offered by metal bats!

(Note: The above can also be used to explain the differences between metal and wooden golf clubs!!)

By: Kenny Morley, Ohio State University 

 

References:

Russel, D. A.. Why Aluminum Bats Can Perform Better than Wood Bats. Retrieved from http://www.acs.psu.edu/drussell/bats/alumwood.html

Maddox, D. (2012). Altitude Plays a Big Role in Denver Baseball. Retrieved from http://voices.yahoo.com/altitude-plays-big-role-denver-baseball- 289433.html

How Air Resistance Determines the Pitch (Basic)

To pitch a the highest level, a pitcher needs strength, flexibility, and intense focus.

When the ball is finally released, several forces act on it. First is gravity. The moment the ball leaves the pitchers hand, gravity begins to make the ball drop toward Earth. Gravity is basically the pull that an object of mass has on another object. Everything on Earth is affected by gravity. For example, a pencil you are using to take a math test has a pull on you and you have a pull on it! The only difference is that you have more mass than the pencil so you cannot feel the effects. The same is true for a baseball.Earth has an effect on the ball but also the ball has an effect on the Earth. However, the force of the ball on the Earth is not seen because of the tremendous difference in mass.

Another force that acts on the ball is air resistance. Air acts just like water! The only difference is that air is much less dense than water. This means that the microscopic air particles are much farther apart than the particles in water.  In a swimming pool, it is much harder to walk than when on land. This is because the water is providing a resistance against your body. Air provides a resistance as well but it is not felt as much because of the density differences. However, since a baseball is much lighter than you, air plays more of a role on a ball than on your body. The ball essentially must move air out of the way and this slows it down.  Imagine a skydiver opening up his parachute and falling slowly to Earth. This is exactly what happens to a baseball but on a much smaller scale.
Air resistance is also responsible for a pitcher being able to throw different kinds of pitches! When a pitcher throws a fastball, he throws it in such a manner that the spin is straight up. This will keep the ball going straight. When the pitcher throws a curve ball, he will tilt the spin so that the air resistance will push the ball in different directions (usually down or to the sides). In the case of a knuckleball, a pitcher will try to put zero spin on the ball. This will allow the air to push the ball in all sorts of directions and it appears to hitters that the ball is “dancing” through the air. This makes the pitch very deceptive and can lead to more strikeouts.

By: Kenny Morley, Ohio State University 

 

References:

Zarda, B. (2008, August 06). Science of a pitching freak. Retrieved from http://www.popsci.com/score/article/2008-08/science-pitching-freak

Free fall and air resistance. (2012). Retrieved from http://www.physicsclassroom.com/class/newtlaws/u2l3e.cfm