Heat

Why does the stethoscope feel colder than a tongue depressor? “Whoa! That’s cold!”

Heat Heat is the transfer of energy between objects that are different temperatures Energy is always transferred from higher-temperature objects to lower-temperature objects until thermal equilibrium is reached.

Heat Thermal equilibrium is the point at which two objects reach the same temperature.

Heat When the doctor’s stethoscope touches your back, energy is transferred from your back to the stethoscope. Why? Your back has a higher temperature!

Heat If heat is the transfer of energy, what form of energy is being transferred? Thermal! What is thermal energy? It is the total energy of the particles. It is expressed in joules and depends partly on temperature.

Heat Thermal energy also depends on the amount of substance you have.

Heat Explain the energy transfer shown below:

The difference between Temperature & Heat Imagine that you heated up these two gold bars to 40 0 C and put them in ice until they reached equilibrium. Which one would melt more ice? Why? What does this have to do with thermal energy?

The temperatures (and, therefore, the average kinetic energies) of both blocks of gold were the same, but the thermal energy they each transferred to the ice was different. Thermal energy is measured in joules while temperature is measured in degrees or kelvins. Thermal energy depends upon more than the temperature; it also depends on the mass of the substance. The difference between Temperature & Heat

Misconception Alert The thermal energy of a substance is related to the substance’s temperature as well as its state. For example, equal masses of liquid water and steam at the same temperature (100 0 C) have different amounts of thermal energy. Why? The steam stores energy used to separate the particles of liquid water to change to steam, therefore the steam has more thermal energy than the liquid water.

Conduction Conduction is the transfer of thermal energy from one substance to another through direct contact.

When two substances come together, particles collide and thermal energy is transferred from higher-temperature substances to lower-temperature substances. (Higher-kinetic energy particles transfer kinetic energy to the lower-kinetic energy particles)

Conductors Conductors are substances that transfer thermal energy well. Iron skillet Cookie sheet Copper pipes Coils on stove Curling iron

Special ceramic tiles were created for use on the underside of the space shuttle. These tiles transfer so little energy that one side can be exposed to a welder’s torch while the other side remains cool to the touch!

Insulators Insulators are items that transfer energy poorly. Flannel PJ’s Fiberglass Oven Mitt Ceramic bowl Plastic spatula

Convection Convection is the transfer of thermal energy by the movement of liquid or gas.

Convection Water on the bottom of the pan is heated by conduction and becomes less dense and therefore rises. At the surface it begins to cool and move closer together and sink again only to be heated…. This creates a convection current – the circular movement of liquids or gases due to density differences that result from temperature differences.

Examples of Convection Currents Space heater Magma in below Earth’s crust Wind

Radiation Radiation is the transfer of energy through matter or space as electromagnetic waves, such as visible light and infrared waves.

The greenhouse effect.

The very dense atmosphere of Venus is composed mostly of carbon dioxide. The high amount of this results in a greenhouse effect that traps most thermal energy from sunlight. The surface temperature of Venus is therefore the hottest of any planet in our solar system. It remains at ~460 0 C-hot enough to melt zinc!