I choose to study the force during avalanches. I think it is interesting to study this because avalanches are a common problem in the mountains where many people dye because of it. This topic is not really known by people who do not study it. As you all known, avalanche is an abrupt and rapid flow of snow, often mixed with air and water. The reason why avalanches occur is because the snow can not stand the weight of the snowpack starts falling down the mountain side.
While it accelerates, several forces start forming. The driving force is always bigger than the resisting forces.This topic will be a challenge for me due to the fact that there is not so much information on it. Many scientific books about this kind of problem have been written due to its terrible harm.
Eventhough the study of avalanches is usually considered as a geography topic, physics is closelly linked with this as well. We set this type of problem into the „dynamics“ section of physics. Dynamics generally talks about the time evolution of physical processes which is exactly like an avalanche force. Section 2.
Goals and Rationale My goal is to learn about this topic as much as possible.I would like to know about the driving force and the motion resistance. Another interesting thing would be to study all the resisting forces. I would be pleasured to study this because it is interesting for me and I do not know anything about it so I would like to learn it. The are a lot of questions in my mind conserning this avalanche phenomena. What kind of resisting forces are there? What is an avalanche impact? Are there different types of forces during an avalanche? How can we calculate the maximum velocity, distance an avalanche makes while travelling in its decelerating phase?I hope I am going to find out soon.
Section 3. Description of the Problem As I have already said, avalanche force is a kind of dynamics. We can also define dynamics as a branch of mechanics concerned with the forces that cause objects to move. We know that there are some forces acting on an avalanche even if we did not know physics. The Newton? s first law of motion states: „An object at rest remains at rest, and an object in motion continues to stay in motion with constant velocity unless the object experiences a net external force.
“ (Izaak Newton).This tells us that if an avalanche starts forming and accelerating, it will only stop untill it hits somekind of impediment or the bottom of the mountain. That is why avalanche is so harmful for people. Someone who is standing in the center of a slope has not got a chance of running away.
The avalanche? s velocity increases when the trajectory increases so the lower you are standing, the worst it is because by the time it gets to you, its acceleration is too high. Section 4. Research of Problem Firstly, I will start speaking about the driving force and motion resistance.After fracture and release of a slab the snow accelerates downslope as an avalanche.
This slab is broken up into a sliding, tumbling, and bounding movement. If it is on a big mountain, the avalanche slowly turns into a flow. Two opposite sets of forces form with or against the flowing avalanche. One is the driving force(F) which is parallel to the slope. Second is the resisting force(R) which is composed of several different forces which are against F preventing the avalanche from accelerating indefinitely. Avalanche will accelerate as long as F is bigger than R because by this a net force will form down the slope.The condition of F having to be bigger than R is only true at the starting zone.
Here acceleration occurs because the slope is steep and F is large. The flowing mass can also increase due to the fact that additional unstable snow will be pushed and conjucted into the avalanche. Constant velocity starts when F equals R. This condition occurs after the starting zone all the way to the botton of the avalanche path. This zone is usually called the track. In fact, the velocity even here changes due to the entering of new snow, deposition and topographic irregulaties but just slightly.
Deceleration occurs in therunout zone where R becomes greater than F. Here the gradient is reduced as well as F. Now, the underlying snow pack is stable and the kinetic energy is dissipated. Next, I will tell you something about the resisting forces on their own. Talking about the resisting forces, there are five important factors contributing to frictional resistance which are: R1: Sliding friction between the avalanche and the underlying snow or ground. R2: Internal dynamic shear resistance due to collisions and momentum exchange between particles and blocks of snow.
R3: Turbulent friction within the snow/air suspension. R4: Shear between the avalanche and the surrounding air. R5: Fluid-dynamic drag at the front of the avalanche. To find out acceleration on an avalanche, we have to know these resisting forces. The formula for this is listed in the documentation. The importance of the individual resisting forces varies within the avalanche and depends on the type of avalanching snow. Lastly, I will teach you somethings about avalanche impact.
Avalanches can produce very large dynamic forces on objects.High velocity, low density, dry snow avalanches may flow over or around objects. This produces a fluid-dynamic stagnation pressure which is calculated by P = 1/2 pV2. Here P is pressure, p is the avalanche density and V is avalanche velocity.
Total force on the object consists of „drag and uplift“ forces which act perpendiculary or parallely to the flow direction and upward on the object(which may for example be a hut in the mountains). Denser, slower moving avalanches will not engulf an object. Some of the avalanche? s mass rest against the object and some is deviated. The equation for this is P = pV2.Because big defferences exist between the mechanics of impact of diffenent types of avalanches, someone must decide which type s likely to occus in that kind of area. Section 5. Documentation The driving force(F) and the resisting forces(R) act on a moving avalanche to determine its acceleration and maximum velocity. Parts of an avalanche path Formula for counting the acceleration of an avalanche Hard slab avalanche flow Slow slab avalanche flow Impact of a dry snow or powder avalanche may produce both drag and lift forces on an object.
Impact of a dense, wet snow avalanche.Works CitedLeaf, Charles. “references.
” avalanche dynamics. 1998-2001. WestWide Avalanche Network. 14 Jan 2009 <http://www. avalanche. org/~moonstone/zoning/avalanche%20dynamics.
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” avalanche dynamics. 1976. Guidelines and methods for detailed snow avalanche hazard investigations. 14 Jan 2009 <http://www. avalanche. org/~moonstone/zoning/avalanche%20dynamics.
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Bauzeitung. 14 Jan 2009 <http://www. avalanche. org/~moonstone/zoning/avalanche%20dynamics. htm>.