Science Culminating Project 2012- 2013
Thermal Energy
Let's review shall we? What are the types of energy?
Thermal, Nuclear, Electromagnetic, Chemical, Mechanical
Among these what category does kinetic and potential energy lie under?
Mechanical ; Potential Energy consists of elastic and gravitational energy
What is temperature?
Temperature tells us whether something is either hot or cold. On a molecular level, temperature depends on kinetic energy of the molecules of a substance. The molecules in a substance are in constant motion. In general, temperature is a measure of the average kinetic energy of the molecules in a substance. We use a thermometer to accurately determine the temperature of a substance. Two common scales are the Fahrenheit and the Celsius scale. Fahrenheit has an ice point of 32 degrees and a steam point of 212 degrees. The Celsius scale has an ice point of 0 degrees and steam point of 100 degrees.
Water Bottles - Don't fill up water bottles to the top because as it heats up, the molecules move faster and thus expands, making the water bottle go POP!
Lava Lamp - The light bulb heats up the "lava": as a result warm "lava" will rise to the top because it has a low density, whereas the cold "lava" will sink because of its high density.
Roller Coasters - Roller coasters use the conservation of energy: total energy stays the same, but can take many different forms- such as kinetic and gravitational potential energy.
Balloon - When putting a balloon and heating it up in the microwave for a few seconds, you find that the balloon starts expanding because it is gaining energy. When taken out of the microwave, it begins to cool down and flattens and condenses ; losing energy.
Shaking Hands - When shaking hands, say for example your hands are warm and the other one is cold. You are giving away thermal energy because energy always goes from hot object ; with highest energy ; to cold object; lowest energy.
Real World Connections
What is Heat?
We commonly state that heat is a form of energy. But let's be more descriptive. The molecules of a substance may vibrate back and forth, rotate, or move from place to place thus having kinetic energy. Kinetic energy is related to temperature. The higher the temperature, the faster movement of kinetic energy of molecules. There is also potential energy in this equation. This is the vibrating and/ or rotational modes of atoms within molecules: also thought of as springs. The total energy ( kinetic + potential ) equals INTERNAL ENERGY!!!
Heat is the net energy transferred from one object to another because of temperature difference. Heat gets transferred from a region of high temperature to a low temperature. When heat is added to the body, the internal energy increases. Some of the energy gets transferred into the kinetic energy of the molecules thus resulting in a temperature increase; and some energy may go into potential energy part of internal energy.
Heat
Units to measure Heat
Because heat is energy, we use the unit ( J ) joule. However it is also referred to as a calorie (cal) or amount of heat necessary to rise one gram of pure water one Celsius degree. ( 1 calorie = 4.186 J ( 4.2 J) ). Kilocaleries (kcal) calorie used to describe diets, is the amount of heat necessary to raise one kilogram of water one Celsius degree. A food Calorie (Cal) = 1000 cal ( 1 kcal) or 1 food Calorie = 4186 joules. One Btu ( unit of heat in the British system) is the amount of heat necessary to raise one pound of water one Fahrenheit degree.
Specific Heat and Latent Heat
Why is it that when heating up an equal mass of iron and aluminum with equal amounts of heat, iron increased by 100 degrees Celsius, whereas aluminum increased by 48 degrees Celsius? That's because the internal forces of the material are different. We express this difference in terms of specific heat or amount of heat necessary to raise the temperature of one kilogram of the substance one Celsius degree. The equation :
Amount of heat to change temperature = Mass X Specific Heat X Temperature Change
When a substance goes from a liquid state to a gas state, the heat energy must go into the work of separating the molecules and not into increasing the kinetic energy, or it will increase the temperature.This heat is called latent heat or "hidden heat." Latent Heat of fusion is the change from a solid to liquid at same temperature, while latent heat of vaporization is the change of a liquid into a gas. The equations used :
heat needed to melt a substance = mass X latent heat of fusion ( 80 kcal/kg)
heat needed to boil a substance = mass X latent heat of vaporization ( 540 kcal/kg)
Heat Transfer
There are three types of ways to transfer heat. The three methods are conduction, convection and radiation.
Conduction is the transfer of heat by molecular collisions . Solids especially metals are the best thermal conductors. Whereas liquids and gas are poor thermal conductors. Liquids, though, are better than gasses because their molecules are closer together and collide more often. Gasses aren't so much because their molecules are relatively farther apart and so conductive collisions don't often occur. These substances are what you refer as thermal insulators.
EX: Cooking pots and pans are made out of metals so the heat can conducts the food inside, but at the end of the pots are made of cloth, a thermal insulator to keep yourself from getting burnt.
Convection is the transfer of heat by the movement of a substance, or mass, from one position to another. You can locate convection in your own home. Homes have this thing called a heater where air is heated at the furnace moves throughout the house by metal ducts below the floor. As warm air rises, cool air is forced to stay on the ground and convection cycles promote a warm house.
Conduction and convection both require a medium for the process to occur. But Radiation does not.
Radiation is the process of transferring energy by means of electromagnetic waves. These types of waves can travel through a vacuum. For example, radiation occurs in an open fire. Though there are three methods of heat taking place. But air is a poor conductor and the air warmed by the fire is rising, fire is not the one that's circulating. So the only acceptable transfer of heat is radiation.Radiation is also why we wear dark clothes in the winter and light clothes in the summer.
