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Just like all physics problems, calculations for latent energy require using the GRASP method.
G – List the Givens
R – List what is Required
A – Analysis – Analyze the problem
S – Solution
P – Paraphrase
When a car brakes, an amount of thermal energy equal to 112,500 J is generated in the brake drums. If the mass of the brake drums is 28.0 kg and its specific heat capacity is 460.5 J kg-1oC-1, what is the change in its temperature?
G– TE (112,500 J), Mass (28 kg), H-C (460.5 K kg)
R – Change in temp
A– Q=MC^T
S – 112,500 = 28 X 460.5 X ^T
112, 500 / 12,894 = ^T
244.30 K = ^6
P – Therefore, the change in temperature in this case is 244,30 K
After Unit Reflection: In this post, I demonstrated an understanding of latent energy transformations and problems. I showed the GRASP solution, and what each letter stands for, and then showed an example calculations.
Latent Heat is the heat required for an object to change phase (melt,boil,freeze etc). In class, the melting of a cube of ice was discussed to explain latent heat, as well as the boiling of water.
The question asked in class was, what are the different temperature time graphs for the melting of ice on a metal lid vs on a plastic lid. The graph shapes were the same, but on the metal lid, the fusion of ice-water was faster since metal is a good conductor of electricity and gives heat faster to the ice to make it melt.
Fusion: When a substance changes from a solid to a liquid
When ice melts, it goes through 5 stages on a temperature time graph. The first is when the temperature of the ice increases when put on a metal surface, then when the ice turns to water, then the temperature of the water increases, then the water turns to steam, and then the phase is fully changed into steam.
Latent Heat Of Fusion: The energy required to transition one unit of a substance from solid to liquid
Latent Heat Of Vaporization: The energy required to transition one unit of a substance from liquid to vapor.
The equations to describe the different transformations and state changes are:
Q=mLf (for melting or freezing). where Q is heat required to change a sample, m is the mass of the sample, and Lf is the latent heat of fusion
Q = mLv (for vaporizing or condensing) where Q is heat required to change a sample, m is the mass of the sample, and Lf is the latent heat of vaporization
After Unit Reflection: In this unit, I demonstrated an understanding of latent heat and state transformations – such as the heat required to change states, and how the temperature changes as a piece of ice melts into water and then steam. This post also showed an understanding of energy transformations that took place as the states of the ice were changing. I also demonstrated an understanding of equations for latent heat of fusion and and latent heat of vaporization.
The question was – if two lids are left overnight, one metal and one plastic, which one would be hotter? After carrying out the experiment, it was proved that they were both very similar, with a difference of 0.2 degrees. However, the question was that, if they were both the same, why does the metal feel colder.
The explanation is that since metal is a good conductor of heat, it can transfer heat and absorb heat from other objects. So, if a person were to touch the metal, the metal would ‘suck’ the heat/thermal energy from the fingers of the person much faster than the plastic would, since the plastic is the insulator. Hence, your hands would feel colder when you touch the metal as compared to when you touch the plastic.
Experiment – water balloon vs balloon without water
The second experiment asked the question that if there were 2 balloons, one with a little bit of water, one without any water, and both of them were put over a bunsen burner, what would happen? What happened was that the one without the water popped much earlier than the one with the water.
The explanation for this is that in the one with the water, the water absorbs the heat from the bunsen burner, so the rubber of the balloon does not heat up and expand as fast, because the heat is being absorbed by the water. The ability of water to soak up and retain heat is really good. In the one without the water, there was no water to absorb the heat, so the rubber of the balloon expands and heats up faster, and hence it pops faster.
After unit reflection: In this post I analysed the lids and water balloons to apply the concepts of energy. By analyzing both the lid and the balloon I applied the concept of kinetic energy and temperature, as well as the concept of heat conduction. By explaining that since metal conducts heat faster, the molecules move around faster, and it can absorb and give heat faster, and how water absorbs heat, these I analyzed and explained these principles.
The First Law of Thermodynamics states that energy can be converted from one form to another with the interaction of heat, work and internal energy, but it cannot be created nor destroyed, under any circumstances.
Internal Energy: Internal energy is defined as the total energy of a closed system. There are 2 types of internal energies – potential and kinetic. The internal energy of an object can be changed by heating it or doing work on it.
Kinetic Energy: Kinetic energy is energy of motion. If work is done on an object by applying a force , the object speeds up and thereby gains kinetic energy. Kinetic energy is a property of a moving object or particle and depends not only on its motion but also on it’s mass.
Heat: Heat is the same as thermal energy. It is defined as the thermal energy that is transferred from one body to another as a result of a change in temperature. Heat transfers from an object that is hotter to one that is cooler. The faster the kinetic energy of an object, the warmer it will be. There are 3 types of heat transfer – conduction, convection, and radiation.
Conduction – Heat transfer through contact
Convection – Heat transfer through movement without contact
Radiation – Heat transfer without contact
Temperature: Temperature is defined as the measure of the average kinetic energy acting on an object. The hotter the temperature, the higher the average speed of the particles.
The temperature unit most commonly used is the Kelvin (K). Like other temperature scales, the freezing and boiling points of water are factors in establishing the scale’s range. There are 100 degrees between the temperature at which water freezes at (273.16 K) and boils (373.16 K). Each unit on this scale is equal to a degree on the Celsius scale. There are no negative numbers on the Kelvin scale, as the lowest number is 0 K.
After unit reflection: In this post, I demonstrated a thorough understanding of thermal energy and the transfer of thermal energy (heat). I identified what heat was first by using a mind map, and then by writing a proper detailed paragraph describing heat. I also described the thee methods of heat transfer – conduction, convection and radiation, and also related heat to temperature.
After Unit Reflection: In this post, I demonstrated an understanding of kinetic energy. I described and explained what kinetic energy was and what does it mean, and I also related it back to heat and temperature, such as stating the fact that the higher the temperature, the higher the kinetic energy.
Power is defined as the rate at which work is done, or at the rate at which energy is transferred.
Power = W/t
P stands for power (in watts)
W stands for the amount of work done (in Joules)
t stands for the amount of time (in seconds)
The standard unit for measuring power is the Watt. From the equation above we can see that power is W/t. The unit for work is the joule (J), so a Watt is the same as a joule/second or J/s.
The second thing briefly talked about was efficiency.
Efficiency is a measure of how much work or energy is conserved in a process.
In many processes, work or energy is lost, for example as waste heat or vibration. The efficiency is the energy output, divided by the energy input, and expressed as a percentage.
After Unit Reflection : In this post, I demonstrated an understanding of power. I defined it, stated the formula and what it means, showed a sample calculation and stated the unit
The amount of dissipated energy equals the gravitational potential energy – kinetic energy.
With no friction, Eg1 = Ek2
2) LOL diagrams show the energy at the beginning, the circle shows what happens, the end shows the change in energy (if any)
The middle part shows a system (in class, we did the Earth/Train System) In physics, system is the name given to a collection of objects that are chosen to model with equations. If we are to describe the motion of an object using conservation of energy, then the system should include the object of interest and all other objects that it interacts with.
The example discussed in class was that of a roller coaster. When the train of the coaster was at point A, it has only gravitational potential energy. When it started moving, there were energy transformations, and by the time it reached the end of the first hill, that potential energy had been converted into kinetic energy.
3) Gravitational potential energy is relative to a reference point.
Environmental Impact Of A Roller Coaster: A roller coaster has massive environmental impacts. It causes a large amount of pollution due to the large amounts of energy needed to keep it running. The large amount of space that is used to build a roller coaster also destroys some habitats and ecosystems.
Questions:
How much does friction affect the energy transformation?
How would we know, without calculation, an estimate if there is more kinetic energy left at the end or more disscapitated energy?
After Unit Reflection: This post shows an understanding of energy transformations, by explaining LOL diagrams and using the example of a roller coaster. I explained that by the time a roller coaster goes from the top of a hill to the bottom of it, the potential energy has been converted into potential energy. This also explains the Law Of Conservation Of Energy.
After Unit Reflection: In this post, I also assessed the environmental impacts of a roller coaster, which is a technology using energy transformations. I talked about how the energy used causes pollution, and the space used may destroy habitats and ecosystems.
Gravitational potential energy is energy an object possesses because of its position in a gravitational field.
3 Things Learnt:
When the force and the displacement are in the same direction, the acceleration will be zero.
The example done in class was sliding 2 marbles down a ramp, both the same distance, but one had a shorter ramp and one had a longer one. What I learnt here was that firstly, when the marbles were on top of the ramp, they had gravitational potential energy. Any object has a gravitational potential energy. Then, as an object travels, it’s potential energy changes into kinetic energy, as happened with the marbles. The question was which one would reach the end of the tracks first, and after experimenting, I learnt it was the one with the shorter ramp, because since it’s ramp was shorter, it would reach it’s highest kinetic energy at a faster rate than the marble on the longer ramp, and since it reached max velocity faster, it would reach the end of the tracks faster.
When determining the velocity and kinetic energy, the mass didn’t matter. When one of the marbles was switched to one of a higher mass (the one on the longer ramp), the question was, would there be any change as to which ball reaches first now. Though the one with higher mass would have a higher potential energy, but that does not affect the situation. The one that reached first was still the one with the shorter ramp, not the one with the higher potential energy. This shows that mass has no effect on how fast an object reaches it’s max kinetic energy.
Questions:
Is there ANY situation where the mass would have even the slightest bit of effect?
How much affect does friction have in this case?
After Unit Reflection: In this post, I investigated energy transformations and the law of conservation of energy. When the ball was slid down the ramp, it’s potential energy converted into kinetic energy, and this transformation was investigated for 2 different sets of marbles. This also showed the law of conservation of energy, as the energy was converted, not lost or created, as the marble went down the ramp.
After Unit Reflection: In this post, I also demonstrated an understanding of gravitational potential energy. I described the term, and showed that the marbles, before being slid down, had gravitational potential energy, as all other objects do. I also explained that this gravitational potential energy is converted into kinetic energy as an object moves.
In physics, a force is said to do work if, when acting, there is a displacement of the point of application in the direction of the force.
Work = Fd, where F = force and d = displacement
Question : If an object is pushed a distance of 4 m with a force of 2.5 N, calculate thee work done.
Work = Fd
Work = (2.5 N)(4 m)
Work = 10 Joules
The unit for work is joules
Work can only be done if there is a displacement. As discussed in class, weight lifters are not actually doing any work, because no matter how many times they pick up the weights and move them, and practice, eventually, they are going to put them back in the standard position, which means no displacement, and hence, no work was done.
The two types of energy briefly discussed today were kinetic energy and gravitational potential energy. Kinetic energy is the energy an object has because of it’s motion. In order to accelerate an object, a force must be applied. This requires us to do work. Once a force has been applied, work has been done, and energy has been transferred to the object, the object will travel with a new constant speed, which is known as it’s kinetic energy.
We also briefly talked about LOL diagrams. These show the energy before the work is done, what happens when the work is being done, and the energy after (what kind of energy is there now? Was there any energy transfer?)
After Unit Reflection: In this post, I demonstrated an understanding of work. I gave the definition of work, the formula, what the letters in the formula stand for, doing an example calculation, and gave an example of how and why body builders actually do not do any work. These show a thorough understanding of the concept of work.
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