Law of Conservation of Energy

Energy is the ability to do work, or to apply a force through a distance. The law of conservation of energy states that energy cannot be created or destroyed. However, energy can be transformed from one type to another. There are many different types of energy we see every day. The table below reviews some of these.

  potential energy energy stored within an object due to its position or configuration, most commonly energy due to an object’s height from the ground (gravitational potential energy) kinetic energy the energy of motionmechanical energy  the sum of the potential and kinetic energy in a systemlightenergy the energy of electromagnetic waves, such as visible light and UV light thermal energythe portion of internal energy responsible for temperature  electrical energy the energy available to move charges through an electrical circuitsound energy  energy carried by sound waves in the vibration of particleschemical energy  energy stored within the bonds of atoms and molecules, also called nuclear energy   Click here to join Tim & Moby at BrainPop© as they explore forms of energy.BRAINPOP© DIRECTIONS: 1)  Click “Play Movie” to begin the movie. You can click “full screen movie”to watch the movie in a larger screen. 2)     Check out the “Q&A” to review important ideas about forms of energy.3)     Want to learn some more? Go to “FYI” to learn cool facts about forms of energy.4)     How well do you understand forms of energy?  Take the “Review Quiz” to find out. This is not an assessment – just practice!  Your score is not recorded.  5)     Close the window and return here to learn more! 

When applying this law to a system, the system must be isolated. Otherwise energy could just leave the system and go into another.

Types of SystemsOpen System – An open system allows mass and energy to travel in and out of the system freely. A cup of ice water is an open system as heat can enter it and warm the drink over time, and more ice cubes could be added later to cool it back down.Closed System – In a closed system mass cannot travel in and out of the system. Energy may or may not travel in and out of the system. The Earth is almost a closed system, as energy enters (from the Sun) but mass seldom enters or leaves the system. Isolated System – An isolated system is the most restrictive. In an isolated system neither energy nor mass can leave the system. Isolated systems rarely, if ever, occur naturally but can be created in a laboratory setting. These are called calorimeters. A Styrofoam coffee cup with a lid tries to be an isolated system by letting out as little heat as possible.  

Mechanical Energy

The easiest type of energy to see the conversion of is mechanical energy, which includes the kinetic and potential energy in a substance. Picture a roller coaster. As a roller coaster moves up a hill it is gaining potential energy due to its increasing height from the ground. As it starts down the hill potential energy is transformed into kinetic energy, causing the roller coaster to move faster and faster. Have you ever noticed that the first hill of a roller coaster is always the highest? This is because a roller coaster is an open system, and some energy leaves the system in the form of heat because of friction between the roller coaster’s wheels and the track. 

  Click HERE to watch the conversion of potential energy to kinetic energy on a roller coaster.  

For each of the situations lists describe what type of energy transfer is occurring. For example, a cell phone ringing. The energy transfer is electrical energy to sound energy. 

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