5.3 Conservation of Energy pp Mr. Richter

Agenda  Collect Progress Reports  Review HW  Intro to Conservation of Energy  Notes:  Mechanical Energy  Conservation of Mechanical Energy  Problem Solving with Conservation of Mechanical Energy  Data Rubric

Objectives: We Will Be Able To…  Identify situations in which conservation of mechanical energy is valid.  Recognize the forms that conserved energy can take.  Solve problems using conservation of mechanical energy.

Conservation of Mechanical Energy

Mechanical Energy  Mechanical energy is an umbrella term for all of the energy that is associated with movement  kinetic energy – moving objects  potential energy – objects that could move  Mechanical energy is another way of saying the sum of the kinetic and potential energy.  Non-mechanical energy (like heat, chemical, electrical, etc.) can be more difficult to model, so we deal with it separately.

Conservation of Energy  When we say conserve in everyday life, we usually mean save, or put aside.  In physics, when something is conserved, it means that it is neither created or destroyed. The total amount remains the same.  Like the money in the classroom.

Conservation of Energy  The total amount of energy in a system does not change.  The Law of Conservation of Energy:  This is only true in the absence of outside forces, like friction.

Conservation of Energy  When objects are moving upward, they lose kinetic energy but gain potential energy.  Kinetic energy converts into potential energy.  When objects are moving down, they lose potential energy but gain kinetic energy.  Potential energy converts into kinetic energy.

Let’s Watch a Video! 

Conservation of Mechanical Energy Formula  Notice that the mass does not matter here. It does not make a difference, because it can be eliminated from every term.

Problem Solving with Conservation of Energy  A 3.0-kg car moving with a speed of 2.0 m/s starts up a hill. How high does the car roll before it stops?  Now try with a 5.0 kg car instead!

Wrap-Up: Did we meet our objectives?  Identify situations in which conservation of mechanical energy is valid.  Recognize the forms that conserved energy can take.  Solve problems using conservation of mechanical energy.

Homework  p185 #2-5, p186 #2,3 Due Wed