Thermodynamics!
Today, we were introduced to the topic of thermodynamics!
With an extensive and in-depth discussion on this topic, I was able to learn a lot about the basics of thermodynamics! Specifically, we related thermal energy with mechanical energy and found how to measure it. Here’s a recap:
1) Temperature is the measure of the average amount of kinetic energy in matter. All matter is made from particles, and these particles vibrate, move, and rotate randomly. Together, these minuscule movements give matter internal kinetic energy, and the average across all particles give us the temperature of an object.
We measure temperature with primarily two scales: Kelvin (K) and Celsius (℃). The Celsius scale uses 0 ℃ as the freezing point of water and 100 ℃ as the boiling point of water at 1 atmosphere. This is very useful for everyday tasks such as weather, cooking, and heating, since most of the temperatures that you encounter daily are close to these values. The Kelvin scale is an adjusted scale that is more adapted for physics applications. Specifically, it sets 0 K as absolute zero, the point when matter has zero internal kinetic energy; the particles are not moving at all. Absolute zero has been found to be -273.15 ℃, and other than this different reference unit, an increase of temperature by 1 kelvin is also 1 ℃. As such, to convert between Kelvin and degrees Celsius, add 273.15 to go from ℃ to K, or subtract 273.15 to go from K to ℃.
2) Thermal energy is the measure of the transfer of internal energy of matter from one body to another. It is also known as heat, and can either change the temperature of a body or have the body undergo a phase change. Thermal energy is expressed in joules, and since it is based on the total amount of internal energy of matter, mass is a key value in determining thermal energy. More massive objects carry more thermal energy.
The conservation of energy still applies when thermal energy is transferred.
There are three ways to transfer thermal energy:
Conduction occurs when two objects are in direct contact with each other.
Convection takes place uniquely in fluids, and occurs through the circulation of fluids. Warmer fluids rise up, while cooler fluids take the place of the warmer fluids.
Radiation occurs all the time in matter with internal kinetic energy, and transfers thermal energy by emitting light. Radiation does not require a medium: matter in between to move the energy.
3) Mechanical energy can be converted to thermal energy. This happens most often during friction, which is why almost all moving things create heat and that energy systems are never 100% efficient. In physics, efficiency is the measure of how much energy is conserved in the desired form of energy after a process. Efficiency is expressed as a percentage.
To calculate efficiency, we simply divide the amount of desired energy output by the amount of energy input from a transfer. The equation would be:
Efficiency = (Energy Output/Energy Input) x 100%
Note that energy is still always 100% conserved with the law of conservation of energy, however when we talk about efficiency, we are focusing on how much energy is conserved in the way we want.
For example, when we push a box down a ramp we aim to convert gravitational potential energy into kinetic energy. However, friction results in some of this energy being converted into thermal energy, which is not what we want. If we consider the box as the system, this thermal energy is what we would consider as “lost” energy, or energy flowing out of the system.
We would calculate the efficiency of the transfer as follows:
A 3 kg box slides down a ramp 2 m high. A photogate measures the final velocity of the box at the bottom of the ramp to be 2 ms-1.
Efficiency = (Energy Output/Energy Input) x 100% Efficiency = (Ek final/Eg initial) x 100% Efficiency = (½mv2)/(mgh) x 100% Efficiency = (½(3)(2)2)/(3(9.8)(2)) x 100% Efficiency = 10% The efficiency of the transfer of gravitational potential energy to kinetic energy is 10%.
After this big influx of new information, I now have new questions about thermodynamics:
1) How did scientists find absolute zero? As far as I know, absolute zero is unachievable at the moment, so without actually achieving absolute zero, how did scientists extrapolate to find absolute zero? How confident are we in our prediction of absolute zero?
2) How do we calculate thermal energy? Does thermal energy depend on any other factors than temperature and mass?
A cool experiment that we did in class showed us how solvents with higher temperatures dissolved solutes faster! This is because their matter has higher internal kinetic energy, meaning that the particles are moving faster and mixing with the solute faster. We can see this through putting a few drops of food colouring in two cups of water of different temperatures. The red food colouring went into the warmer water and the blue food coloring went into the cooler water. Observe how the blue food colouring remains at the bottom while the red food colouring gets mostly mixed!
After Unit Reflection
Investigation of Energy Transformations
In this blog post, I investigated how the law of conservation of energy applies to energy transformations concerning thermal energy. I noted that the law of conservation of energy also applies to thermal energy (1st law of thermodynamics). I also learned that mechanical energy can be transformed into thermal energy, and that this happens all the time with friction on moving objects.
Understanding Energy - Efficiency
In this blog post, I demonstrated an understanding of efficiency in physics through investigating transformations of mechanical energy into thermal energy! I noted that efficiency of a system is about the ratio between the amount of energy outputted in our desired form and the amount of energy inputted. I made the key observation that energy transformation systems are never 100% efficient in real life, since although the law of conservation of energy still applies, some of it is always transformed and “lost” into thermal energy. I applied my knowledge to solve for the efficiency of an energy transformation from gravitational potential energy to kinetic energy via a box on an inclined plane.
Understanding Energy - Thermal Energy Transfer
In this blog post, I showed my understanding of heat: the transfer of thermal energy. I discussed the three different ways to transfer thermal energy and their properties. Conduction needs contact, convection moves fluids, and radiation can happen anywhere. I noted that in a vacuum, the only way to transfer heat is through radiation, which does not require a medium.