When you’re hot, you’re hot!

Diffusion  Particles in a liquid or gas will spread out. Particles move from areas of high concentration to areas of low concentration. Particles move until they are evenly spread out.

Diffusion  Diffusion occurs because the particles in gases and liquids are moving.

Liquid Diffusion: Dye in Water  What causes the particles to spread out?

Diffusion of a Gas  Where is it coming from?  How does it spread out?

Diffusion  How can the particle model (meaning atoms/molecules are moving) explain these facts about diffusion? Diffusion occurs in liquids and gases, but hardly at all in solids. Diffusion happens more quickly for gases than for liquids. Diffusion happens more quickly at warm temperatures than at cool temperatures.

Heat Energy/Thermal Energy  Heat energy and thermal energy are the same thing.  Thermal energy (heat) is the kinetic energy (or motion) of the particles in an object.  When the particles in the object move faster, the thermal energy of that object increases.  This makes the object feel warmer.

Kinetic Energy (motion)  All matter is made up of particles moving constantly in random directions.  Kinetic energy (heat) is the energy of a particle due to its motion. When particles collide, kinetic energy (heat) is transferred between them. Like how a bowling ball transfers energy to the bowling pins it hits.

Temperature  Thermal energy (heat energy) is measured as temperature.  Temperature measures the average kinetic energy (heat) of an object’s particles.  The more thermal energy (heat) in an object, the higher the temperature.

Temperature  There are three common scales for measuring temperature (heat energy). Fahrenheit Celsius Kelvin

Temperature Scales  This is how the scales compare: FahrenheitCelsius Kelvin (Based on Absolute Zero*) Where Used Mostly USA Most of the World Physical Science Freezing Point 32°0°273 K Boiling Point 212°100°373 K * Absolute Zero = temperature at which ALL molecular movement stops.

Heat  Heat is the movement of thermal energy from one substance to another.  Heat always moves from areas of high thermal energy (hotter) to areas of low thermal energy (cooler).  Heat transfer: Draw arrows to show the direction of energy transfer: « «

Heat  Heat flows in only one direction. Example: cooking an egg  Heat will continue to flow until both objects have the same temperature.  There is no such thing as “cold” – there is only the absence of heat. Heat flow: Hot stove element » frying pan » egg

Thermal Expansion and Contraction  Materials expand as their thermal energy (heat) increases (when they are hotter)  Materials contract as their thermal energy (heat) decreases (when they are cooler)

Construction Expansion Joints  Cracks in sidewalks and roads allow for expansion and contraction during weather changes

Let’s review!  Diffusion says particles will spread out.  Particles will move from high concentrations to low concentrations.  Thermal energy (heat) is the kinetic energy (motion) of the particles in an object.  Thermal energy (heat) is measured as temperature.  Three scales: Fahrenheit, Celsius, Kelvin.  Heat is thermal energy moving from one object to another.  Heat only flows in one direction – from high to low.

Review Questions:  Name 3 common temperature scales and give the freezing and boiling points of water for each scale.  Are thermal energy and temperature the same? Why or why not?  How is the motion of the particles in an object related to its thermal energy?  Can a container of cold water have the same energy as a container of hot water? Explain.

“Mr. Edwards, may I be excused? My brain is full.”