Week 2

• Temperature - the measure of the average kinetic energy of the particles in an object
• Heat - a form of energy that is transferred between systems or objects with different temperatures 
• Change of Phase - a phase change is a physical process in which a substance goes from one phase to another
• Heat-Related Diseases - This often occurs when a person is exercising, working, or engaging in an activity when temperatures and humidity are high.
• Effects of Heat Transfer - The basic effect of heat transfer is that the particles of one substance collide with the particles of another substance.
• Matter consists of trillions upon trillions of molecules and atoms. Each of these particles possesses potential and kinetic energy.
• The sum of potential and kinetic energy of all the particles is called the internal energy of the body.
• Adding heat or thermal energy in a substance increases its internal energy.
• Heat transfer occurs continuously until two bodies in contact acquire the same temperature. At this condition, the two bodies are in thermal equilibrium.
• Heat always flows from the material with a higher temperature to the material with a lower temperature until thermal equilibrium is reached.
• Since heat is a form of energy, the SI unit of heat is Joule (J), defined as the amount of energy needed to raise the temperature of a given mass by one degree.
• Heat is expressed in the unit of calories (cal) which is further said to be the heat energy needed to increase the temperature of 1 gram of clean water by one degree Celsius.
• Sometimes kilocalorie (kcal) is also referred to as a unit of heat where 1 kcal = 1000 cal.
• It is evident from everyday life experiences that temperature is associated with the hotness or coldness of an object.
• When heat is absorbed by an object, the added energy causes the molecules to vibrate. Each molecule interacts with its nearest neighbors and causes them to vibrate, too.
• The more heat is absorbed, the greater is the vibrational motion of the molecules.
• The greater the average vibrational speed of the molecules, the higher the temperature.
• The lower the average vibrational speed, the lower the temperature.
• Recall that the kinetic energy is the energy in motion. Thus, temperature is a measure of the average kinetic energy of the vibrating molecules of the body.
• Heat refers to the transfer of energy from one object to another because of the temperature difference. Unlike this, temperature does not involve a transfer of energy.
• Generally, temperature means the hotness or coldness of an object. You can determine an object's temperature by how fast its molecules are moving.
• Heat makes molecules spread out and turn into gas, cold makes molecules squeeze together and turn liquid or solid.
• The matter may exist in four phases or states. A phase change is when matter changes from one state (solid, liquid, gas, plasma) to another. At certain temperatures, a substance can undergo phase changes.
• Thermal energy from the surroundings is either absorbed or released by the substance undergoing a phase change. During a change of phase, the temperature of a body remains constant.
• In solids, thermal energy is absorbed by the molecules to overcome the strong force that holds them to become liquid. This process is called melting.
• In liquids, thermal energy is absorbed by molecules to break the weak attractive force that holds them to become gas. This process is called evaporation.
• A phase change may also occur when a substance releases heat or thermal energy in the environment.
• When a liquid releases thermal energy, it becomes solid. This phase change is called freezing. It is the reverse of melting.
• Hevaporation (thermal energy absorbed) = Hcondensation (thermal energy released)

  Hmelting (thermal energy absorbed) = Hfreezing (thermal energy released)
• The heat energy added/removed during a phase change is used only to separate the molecules and not to increase the kinetic energy of the molecules.
• When the phase change is completed and heat is continuously added/removed, the heat energy will cause a change in temperature.
• Heat-Related Disease range from mild conditions to very serious conditions. They occur when the body is not able to transfer heat effectively or the body absorbs excessive heat due to extremely high temperature in the environment.
• When a gas releases thermal energy, it becomes liquid. This phase change is called condensation. It is the reverse of evaporation. The amount of thermal energy absorbed by a substance in the melting process is equal to the amount of thermal energy released when the same substance undergoes freezing.
• The following are some common heat-related illnesses:

  • heat rashes
  • muscle cramps
  • fainting
  • heat exhaustion
  • heat stroke
• Heat stroke occurs when the average body temperature is above 40°C. In this condition, the internal systems of the body start to shut down, which results in damage to many of the organs in the body.
• Heat transfer is defined as the movement of heat across the border of the system due to a temperature difference between the system and its surroundings. Interestingly, the temperature difference is said to be a ‘potential’ that causes the transfer of heat from one point to another.
• The transfer of heat may occur in three ways: conduction, convection, and radiation.
• The transmission of thermal energy by conduction occurs in solids and fluids (gases and liquids), but the effect is more evident in solids.
• Radiation is the transfer of thermal energy by electromagnetic waves.