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@vmaccc-blog
Our first day of service saw us in Canto Grande. This poor barrio (called a ‘pueblo joven’ in Peru) is on the outskirts of Lima. It is there that the Christian Brothers run a school called ‘Fe y Alegria 26’, one of a system of schools funded by the government but run by religious communities which…
Entropy
Nature has the tendency to go from order to disorder, from organized to disorganized. an example of entropy is ice melting in a warm room. Entropy is a part of thermodynamics that should always be understood with the first law of thermodynamic; heat flows from hot to cold.
Temperature, Thermal Energy, and Heat (flow) are three separate terms.
Temperature is the average KE of a molecule which the formula 1/2mv^2 represents.
Thermal Energy is the total (heat) energy of all of the molecules of an object and is represented by N x (KE)/#molecules.
Heat (Flow) is the movement towards thermal equilibrium and is based on temperature.
nice post nick, the differences among these three terms are important
Thermal Energy stuff
It's important to be able to distinguish between thermal energy, heat, and temperature. Thermal energy is the total energy of the molecules of an object. A glacier, for example, has a large amount of thermal energy. Heat is the flow of thermal energy. Heat can flow through radiation, convection, or conduction. Temperature is an average of the kinetic energy of an object's molecules. Temperature causes temperature change with two objects, not thermal energy.
The importance of sig figs...
On today's test, I heard many students asking questions about sig figs. I don't think it was the number of sig figs they were concerned about, but it dealt with dimensional analysis. It is important to know the breakdown of units such as Newtons and Joules to make it easier to check dimensionally. For example, a Joule is a (kg)(m^2)(s^-2), and a Newton is a (kg)(m)(s^-2). Also, when the questions dealt with specific heat, the reference chart gave them to us as (J/KgK). Therefore, it was important to make sure that the mass of whatever object the question gave would be converted to match the specific heat's mass component.
Mechanical Systems
There are two kinds of mechanical systems: ideal and non ideal systems. In an ideal system, forces due to friction and air resistance are absent. Most systems in reality are non ideal systems. In an ideal system, all the energy can remain in the system. With a non ideal system, energy may leave the system, but that energy is not destroyed. It left the system most likely as heat due to friction.
Beautiful
wait, how can you set potential energy equal to kinetic energy? wouldn't that only be the case halfway down the system when ke and pe would be equal?
This video displays several pendulums, each of different lengths, resulting in visual patterns. Each pendulum conserves energy throughout the ball's path. When the ball is at one of the ends of its path, its potential energy is a maximum and its kinetic energy is a minimum. At the center of the path, the potential energy is a minimum and the kinetic energy is a maximum. The kinetic energy in the middle of the path = the potential energy at the end of the path = the total energy in the system. The fact that the pendulum's return to starting position and the original pattern shows that both energy and momentum were conserved.
Energy
Today I learned about kinetic and potential energy. The total energy in a system is always conserved. When viewing a problem dealing with a ramp, you can always find the kinetic and potential energy at every point on the ramp, assuming you are given the height at that point. You also need to be given the height where the kinetic energy is 0, because that allows you to figure out the total energy in the system. If a ramp goes from its highest point, to 0m above ground, the potential energy will equal the kinetic energy exactly half way down the ramp.
conservation of momentum throwback. This device, known as a Newton's Cradle, consists of 5 steel balls. When one ball is lifted and released, one ball on the other side will swing out. The same goes for two balls as well. Ideally, the motion would never end, but in reality it will. This is because of the fact that no collision can be perfectly elastic, and also because some energy is lost due to friction in the suspension system.
A bow is a perfect example of the conversion of potential energy to powerful kinetic energy. When an individual pulls the bow string back, potential energy is built up; if you let go of the string the energy is converted to kinetic energy sending the arrow at a high velocity. The more weight it takes to pull the bow back, the more power that is built up. For example, my bow is set to a 60 pound pull back and my cousins is at 70 pounds. Because of our draw weight difference, the velocity of the arrows differ as well- his obviously has a faster velocity than mine. However, when hunting not that much power is completely necessary. A bow with a 45 pound pull back can still get the job done- showing the actual power that can be produced.
Nice example. It would be interesting to calculate the difference in initial velocities among different draw weights. I would assume a proportional relationship to exist between draw weight and arrow speed, assuming no real difference in arrows used is present. Btw, up that 60 pounds and stop being a woman! #sensitivesteve
This is a video of Yash, a champion. We used this to calculate his horsepower and watts (much less than mine, cuz yash is frail). By multiplying the feet traveled (y axis) by pounds and dividing by seconds, then dividing by 550, we found horsepower
Today in class we learned about work. Work is represented by the equation W = F(distance). F is in Newtons and distance is in meters, and work is measured in Joules (J). When breaking a J down, you are left with N (m), or kg(m/s^2)(m), or [(kg)(m^2)]/(s^2). Work is present whenever a force is applied to move an object (change its velocity) over a distance. In a frictionless, gravity absent universe, if an object is moving in mid air at 5 m/s, and someone catches up to that object, takes is while moving 5 m/s and continues to move 5 m/s, no work is being performed. This is because (I may be wrong) work is relative to the object being acted upon. If nothing is accelerating (changing its velocity), no force is being applied, and no work is being performed.
All the equations are the same!
J = (F)(deltaT) = (m)(deltaV) = deltaP. These equations all have to do with the simple Force equation of F = ma. For example, take (F)(deltaT) = m(deltaV). If you isolate force, you are left with F = [(m)(deltaV)]/(deltaT). This is the same as F = MA since A = deltaV/T. You can check that these equations are all the same because of their units. If you solve a problem using F(deltaT), your answer would end up as (Newton)(seconds). If you use m(deltaV), you end up with (kg)(m/s). Newtons x Seconds = kg x m/s. A Newton is (kg)(m/s^s). When you multiply a Newton by a second, the second cancels out with the square of the second from the Newton, leaving you with kg x m/s, which is what you would get if you used the equation m(deltaV). While all these equations are the same, they are really useful because they allow you to solve for an impulse using different known constants.
Momentum
If in an elastic collision no energy is lost to the environment, is it possible to have a truly elastic collision in the real world? Even if you collided two elastic materials such as rubber balls, wouldnt air resistance cause a loss in momentum?
Yes but wouldn't it be safe to say the air resistance on two collided rubber balls would be so minuscule that it could be negligible? I think the first question you posed is interesting, and I would guess the answer is no, but I don't think air resistance is the reason. Momentum is ALWAYS conserved, so air resistance would not lead to a LOSS in momentum. If air resistance was a factor, it would be a transfer of momentum.
Air resistance
Today mr.love showed me a video of a crazy animal who jumps off cliffs with nothing other than a wing vest. The reason he could do this is because of air resistance and lift. Ps steve smells bad right now
In an elastic collision, kinetic energy is not lost, because there is no deformation of an object. This video shows that in an elastic collision, the object is temporarily deformed, but then returns to its normal state. In this video, a gold ball strikes a steel plate at 150 miles per hour. If we knew the mass of the golf ball and converted the miles/hour to meters/s, we could calculate its momentum.
