Have You Ever Pondered About The Friction Of Your Running Shoes

The running shoe had treads going across in curved lines, so it would slow down the shoe moving forwards or backwards, but because of the curve in the lines, to stop sideways (sideways stopping friction) would have to have the most friction force to overcome the friction. That shoe did however, have all of its friction forces (starting, sideways, forward frictions very close.

Frictional forces surround us. We rub our hands together to generate heat when we're shivering. Screeching tires burn rubber on the road when cars start too quickly or turn too sharply. Meanwhile, special treads on those same tires cling to the road to keep us safe when we travel icy highways. And who hasn't been grateful at least a few times for the traction exerted from rubber-soled running shoes or water sandals in slippery situations?

We all recognize what friction is, but do you really understand what causes it? This project focuses on friction, its causes and forces and specifically how it affects how fast you can slip down slides. To get you started, check out the project video. It shows how two talented athletes, Emily and Jenn, explored ways to increase speed down a slide. They applied their results to similar tests in their favorite winter sport, the luge. Few of us have Olympic-quality luge runs readily available in our neighborhoods, or can handle the 65 mph speed down a narrow icy chute, so we provide directions on how you can use a standard neighborhood slide to run your experiments on friction.

In the video, Emily and Jenn focused on different techniques to get a quicker push from the top of their luge runs. Ultimately, it's the frictional interactions all along the run that really influence travel speed down to the bottom. Understanding the physics and molecular forces that determine why things slip or grip as they move across surfaces is the goal of this science project.

Running shoes place high importance on performance and functionality. Ergonomics are also pretty high on the list, but aesthetics are not quite as important, maybe. The overall struggle that you'll probably encounter in running shoes is the balance between performance, ergonomics, life span, reliability, and compatibility (due to different foot types).

A big struggle with shoes is overcoming the different foot types. A neutral foot is easy to deal with, but what about someone with an over-pronated footstrike (foot rolls in) or a supinated foostrike (foot rolls outward)? A neutral runner can get the best performance because his shoe does not require a lot of additional support. Therefore, the shoe can be lighter, more flexible, etc. A pronated foot will require a lot of additional support, and therefore the shoes will be less flexible.

Concerning the more PHYSICS aspect of this, we're going to look at a neutral foot for ease. Running shoes are differently constructed based on their purpose. A training shoe for long distance runners will be considerably more durable and "cushy" than a racing shoe. A long distance shoe or training shoe needs to protect the runner from impact, since impact can damage the joints and is painful. The midsole will probably be pretty soft, with a heel that is more resistant to compression and the forefoot area being even MORE resistant to compression than the heel area. Also, the heel and forefoot areas would be made to absorb shock more than the center of the foot. This makes sense, because the center of the foot (arch) does not take very much impact. The heel and forefoot areas take higher impacts, and therefore must be made to take those impacts.

Furthermore, they also need to be resistant to compression (particularly the forefoot) because if the midsole compresses a lot, the runner will be wasting a lot of energy in compressing the midsole rather than putting that
 energy into motion. It would be like running in sand!

We most commonly think of friction in terms of surface roughness, like the resistance of two pieces of sand paper catching between our fingers. But there are also small electromagnetic interactions of atoms and molecules sitting on the surface of even smooth objects that are important in generating friction. These tiny but strong molecular snags are especially apparent between very smooth surfaces like two pieces of plate glass that stubbornly stick to each other if not separated by paper or sheets of plastic.

In general, when two objects interact they produce some level of frictional force upon each other determined by their weights and the combination of surface roughness and intermolecular sticking. How much friction the two surfaces produce determines whether the objects move or simply remain in place.

We have learnt that our hypothesis is incorrect, yet are not entirely sure if our experiment was accurate. For our next experiment, we will definitely have clearer jobs and try to read the force meter faster and more accurately.