Law of Conservation of Energy

Aim: How to apply the Law of Conservation of Energy

Motivating Idea: How does food provide energy for your body? (chemical potentaol energy is stored in the chemical bonds between atoms in the food. When you digest the food, your body breaks down the molecules in the food, breaking the chemical bonds and releasing energy.

Do Now: Science Writing Journal,  20 points each 1. Describe the nature of energy  2. Define kinetic energy and recognize objects that have it  3.   Describe general nature of potential energy   4.  Distinguish between gravitational, chemical, electrical, elastic and nuclear potential energies and give examples  5.    Apply the law of conservation of energy to situations in which energy is converted from one form to another 

Notes:   ppt. & glencoe 
1.Energy is the ability to cause change. Joule- the SI unit used to measure energy. Kinetic energy – energy in the form of motion. The amount of KE an object has depends on its mass & its speed. KE=½ mv2 

2. potential energy- energy stored in a motionless object, giving it the potential to cause change. Elastic potential energy stored by things that stretch or compress. (slinky) chemical potential energy-energy stored in chemical bonds between atoms. Gravitational potential energy-energy stored by things that are above Earth. a)the amount of GPE an object has depends on its mass, the acceleration due to gravity, and its height above ground. b)GPE= mass in kg times 9.8m/s 2 times height in meters.
3. Energy conversions_ energy changing from one form to another. a) fuels store energy in the form of chemical potential energy. b) mechanical energy- the total amount of potential and kinetic energy in a system.

4. Law of Conservation of Energy- energy may change from one form to another but the total amount of energy never changes.

a)example- as a swing moves back and forth, its energy continually converts from kinetic to potential and back.  b) if the energy of the swing decreases, then  the energy of some other object must increase by an equal amount.   c) friction converts some of the mechanical energy into thermal energy.

5. converting mass into energy- you must think of mass as energy when discussing nuclear reactions. The total amount of mass and energy is conserved. a) Nuclear fusion- two nuclei are fused together-takes place in the sun.  b) Nuclear fission-two nuclei are broken apart.

6. conservation of energy in your body: a) Chemicalo potential energy from food that is stored in your body is used to fuel the processes that keep you alive. b) The food calorie is used to measure how much energy you get from various foods. One Calorie is equivalent to about 4,180 Joules.

Activity: What are some characteristics of a substance that affect its ability to absorb or release thermal energy (heat) .

  (Text book)  page 121 #22 -23.  Calculate kinetic energy using K.E.= ½ mv2  

Calculate changes in gravitational P.E. near the earth’s surface using PEg= Fwh     or     PEg = mgh

Homework: Writing Journal:  Discuss an example of how nuclear reactions, in which mass is converted into energy,  the total amount of (mass + energy) does not change.  Do pages120-121#1-25

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