Do Now List at least 2 differences between heat transfer through conduction and heat transfer through convection. 3.5 minutes Do Now Check

By the end of the day today, IWBAT… Explain and apply the 1 st Law of Thermodynamics By the end of the day today, IWBAT… Explain and apply the 1 st Law of Thermodynamics Why it matters in LIFE: Provides a framework for understanding real- life examples of motion and energy Why it matters in THIS CLASS:

Agenda Do Now5 min Heat Transfer Clarifications5 min 1 st Law of Thermo10 min Examples10 min Practice20 min

Just to Clarify… 1. Heat always travels from low to high. 2. Conduction occurs in fluids only. 3. In convection, the particles actually move from one place to another. 4. Radiation can occur in a vacuum. 5. Popping popcorn in a microwave is an example of conduction. High to low Convection TRUE! radiation

1 st Law of Thermodynamics Energy cannot be created or destroyed, only transformed from one form to another ……look familiar?

Quick Review… What type of energy? This would be true…… in a perfect world. KE PE

Let’s be real…. In reality, the ball would be going slower when it gets back to me (because of air resistance) If the ball is going slower, that would mean that it lost KE (1/2mv 2 ) BUT I THOUGHT ENERGY CAN’T BE DESTROYED!!!??!

Think MOLECULAR As the ball moves through the air, it is bumping into molecules of air. As it bumps into these molecules, KE is transferred from the ball to the particles of air. As the molecules gain KE, their temperature increases. This is a transfer of HEAT.

Recap  What type of energy does a ball have as it is thrown up into the air?  What type of energy does the ball have at the top of its trajectory?  In real life, what happens to the ball’s velocity as it returns to you?  What does this mean for the ball’s kinetic energy?  What accounts for this “loss” of KE?

Recap  What type of energy does a ball have as it is thrown up into the air? Kinetic  What type of energy does the ball have at the top of its trajectory? Potential  In real life, what happens to the ball’s velocity as it returns to you? Slows down due to air resistance!  What does this mean for the ball’s kinetic energy? Should Increase, but…  What accounts for this “loss” of KE? E is transferred to the surrounding air through “air resistance.”

What is internal energy?  Internal energy (U) is the TOTAL energy of an entire system  Kinetic energy of moving molecules  Potential energy of chemical bonds  And anything/everything else!

If the internal energy of a system is changing, your system is either having something done TO it, or it is DOING something to someone else In other words, energy is being transferred INTO the system or OUT of the system

∆U = Q – W Change in internal energy Heat added (+) or removed (-) Work done to (+) or by (-) the system $$ in your bank account Wire transfersChecks Both ways to take energy/money into or out of the system/account

Examples  If 10 J of energy is added to a system that does no external work, by how much will the internal energy of that system be raised?  10 J  If 10 J of energy is added to a system that does 4 J of external work, by how much will the internal energy of that system be raised?  6 J

Real-Life Examples  Throwing a ball into the air  some KE is transferred to the air particles it bumps into (air resistance)  Pushing a desk across the floor  some of the KE is transferred to the particles in the ground (friction)  Blender  work done by the blender is transferred to the molecules of the substance, which increases the internal energy of the substance

Practice!  Complete the problems on the back of your notes sheet  Raise your hand if you have a question