Predicting Change

Claimed by myoung65 on 11/8/2015

The Main Idea

Predicting energy change is simply trying to figure out how energy moves throughout the universe without being created or destroyed, but simply by changing form. Energy makes everything happen, and every time something changes, there is an energy change associated with it. In a very simplistic form, you can predict that when you turn on an oven, it will get hot. Energy is not being created because the temperature increases, the oven is just converting energy from electricity into heat, and we predict that the temperature of the oven will increase. An easy way to predict energy change is to look at thermal energy and how that changes when two substances of different temperatures interact. This can also be described by the conservation of energy principles, which states that energy is neither created nor destroyed. This can be a mind boggling topic simply because energy always seems to be coming from somewhere, so where does it go? The main idea behind why energy is conserved and neither created or destroyed is that it is just transferred to other forms. The first law of Thermodynamics states that the amount of energy in the universe is a constant, fixed amount. It doesn’t go away and it doesn’t appear randomly.

A Mathematical Model

∆Et =mC∆T=Q m is the mass of the object, usually in grams because C has units of J/g◦C C is the specific capacity, and is different for all materials. Units = J/g◦C. C for water is 4.2J/g◦C ∆T is the final temperature minus the initial temperature in ◦C The mathematical equations that are used to model this conservation of energy include many different equations, but they all relate back to the energy principle, ΔEsystem = WSurr +Q. W is the work cone by the surroundings and Q is the thermal energy. The change in energy will be always zero because energy is transferring to other forms of energy within the system or surroundings. Other Important equations include: K = ½mv2, ΔUg = mgΔh, E = K + U, Ei = Ef, Ki + Ui = Kf + Uf, W = F̅Δs cos θ.

A Computational Model

This video shows how energy in conserved in a variety of situations, and highlights how heat plays a role in energy conservation. http://study.com/academy/lesson/first-law-of-thermodynamics-law-of-conservation-of-energy.html

Examples

Simple

Question: State the law of conservation of energy and explain the law by taking an oscillating simple pendulum as an example.

Answer: The law of conservation of energy says that energy can neither be created nor destroyed but can be transformed from one form to another. In the case of the simple pendulum when the bob is as far to the left as it can be, it has maximum potential energy as it is raised with respect to the mean position, but its kinetic energy is zero as the bob stops oscillating for a fraction of a second before moving towards the right. When the bob reaches the mean position, it has a zero potential energy but maximum kinetic energy (maximum velocity too). When the bob of the pendulum swings to extreme right, it has the maximum potential energy but zero kinetic energy.

Middling

Question: A nail becomes warm when it is hammered into a plank. Explain why.

Answer: A raised hammer has potential energy due to its position above the ground, gravity acts as acceleration. When the hammer comes down and strikes the head of the nail, the potential energy is transformed into kinetic energy. If we continue hitting the nail to secure it, the kinetic energy of the hammer is transferred to the molecules of the material of the nail. The heat content of the body is the total energy that the body possesses (Q in the equation above). As the heat content of the body increases, the nail becomes warm.

Difficult

Question: A stone of mass 10 g placed at the top of a tower 50 m high is allowed to fall freely. Show that law of conservation of energy holds good in the case of the stone. http://images.tutorvista.com/contentimages/science/CBSEIXSCIENCE/Ch146/images/img179.jpeg Answer: In this case we have to prove that total energy at A, B and C is the same. Height = 50 m Potential energy at A = mgh = 0.01 x 9.8 x 50 = 0.01 x 98 x 5 = 4.9 J = 0 Total energy at A = potential energy + kinetic energy= 4.9 + 0 Total energy at A = 4.9 J ...(1) At B Height from the ground = 40 m Potential energy = mgh = 0.01 x 9.8 x 40 = 0.01 x 98 x 4 Potential energy at B = 3.92 J To calculate v we make use of III equation of motion, Here, u = 0, a = 9.8 m/s2 and H = 10 m = 0.98 J Total energy at B = potential energy + kinetic energy = 3.92 + 0.98 Total energy at B = 4.90 J (2) At C Height from the ground = 0 Potential energy at C = mgh To calculate v we use III equation of motion, Here, u = 0, a = 9.8m/s2 and H = 50 m = 4.9 J Total energy at C = potential energy + kinetic energy = 0 + 4.9 Total energy at C = 4.9 J (3) The total energy at A, B and C is 4.9 J. This means that law of conservation of energy holds good in the case of a stone falling freely under gravity.

Connectedness

I am interested in this topic because Physics has never really clicked in my mind and researching more on why when you do work on a system the energy is conserved is very interesting to me. I learned a lot why doing this and now understand why this is true instead of just memorizing that it is true. The heat part of the energy principles was especially confusing, but learning how heat energy takes form was very interesting.
This is connected to my major because I am a Biology/Pre-Health major and I am interested in making medical products that increase the efficiently of hospitals. This concept can be important because I will want to design products that use as a little energy as possible while still getting the job done effectively.
The industrial application that can be used concerning this topic is that certain materials can be used when building structures to minimize thermal energy lost, thus making the system more effective.

History

In 1847 James Prescott Joule gave a lecture entitled On Matter, Living Force, and Heat, and he characterized many terms that are closely related to thermal energy and heat transfer. He identified the terms latent heat and sensible heat as forms of heat each effecting distinct physical phenomena, namely the potential and kinetic energy of particles, and thermal energy transfer falls into this category. The units for energy, J, Joules, are named after James Prescott Joule, whose work led to the discovery of the first law of thermodynamics. There are many other people who contributed to the Conservation of Energy laws as a whole. In 1639 Galileo, who was from Italy, introduced the pendulum where potential and kinetic energy are always present in different amounts throughout the motion. French physicists Gottfried Wilhelm Leibniz formulated how Kinetic energy is connected to velocity and mass between 1676-1689. How kinetic energy and Work are related was described by Gaspard-Gustave Coriolis and Jean-Victor Poncelet from 1819-1839 in France. All of these men, along with many others played a very important role in formulating what we know about energy today and they did is because they were constantly trying to make improvements to society and science.

Predicting Change

Contents

The Main Idea

A Mathematical Model

A Computational Model

Examples

Simple

Middling

Difficult

Connectedness

History

See also

Further reading

External links

References

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