Energy 8th Grade Mrs. Boguslaw
What is energy? Energy = the ability to do work When one object does work on another, energy is transferred from one object to the other Measured in Joules (J) …like what other thing we just studied?
Kinetic Energy Kinetic Energy = the energy of motion All moving objects have kinetic energy KE = mv2 2
Calculating Kinetic Energy mv2 KE = What is the kinetic energy of a car that has a mass of 1200 kg and is moving at 20 m/s? 2
Kinetic Energy KE = At the same speed, which will have more kinetic energy, a small car or a large bus? Why? mv2 2
Kinetic Energy KE = Which do you think would have more of an effect on kinetic energy - changing the mass or changing the speed? Why? mv2 2
Potential Energy Potential Energy = the energy that an object has because of the position, shape, or condition of the object A stretched bow has potential energy stored in the string A book on a shelf has potential energy because of gravity
Gravitational Potential Energy GPE = weight x height When you lift something, you use a force that is against gravity and transfer energy to the object Depends on where your “ground” is - based on point of view!
Mechanical Energy Mechanical Energy = the amount of work an object can do because of potential and kinetic energy the total energy of both the motion and position of an object
Mechanical Energy Mechanical Energy = potential energy + kinetic energy ME = PE + KE
Thermal Energy Thermal energy = all of the kinetic energy due to the random motion of the particles that make up an object The warmer an object is, the faster the particles move —> more thermal energy!
Chemical Energy Chemical energy = energy that changes as atoms are rearranged A form of potential energy - depends on the arrangement and position of atoms in a compound Example: digesting food
Electrical Energy Electrical energy = the energy of moving electrons Until you plug in an electric device, it is potential energy
Sound Energy Sound energy = vibrations in the air transmit energy Example: in a guitar string, energy is stored as potential energy as you stretch it. When you let it go, potential energy is turned into kinetic energy that vibrates the string, which vibrates air particles and makes sound
Light Energy Light energy = the vibrations of electrically charged particles Light energy does not have to be carried through matter - it can move through a vacuum!
Nuclear Energy Nuclear energy = energy that comes from changes in the nucleus of an atom Atoms have a lot of potential energy because of the position of particles in the nucleus of an atom When two nuclei join together or one splits apart, lots of energy is released The energy of the sun is nuclear energy
Energy Conversions Ch. 5, Sec. 2
energy conversion a change from one form of energy to another any form of energy can change into any other form of energy
Highest PE Least KE Highest KE Least PE
elastic potential energy you can stretch a rubber band and store energy in it when the rubber band is let go, the potential energy is converted to kinetic energy
how does a light bulb convert energy? electrical energy —> light energy AND… heat energy
how does a battery convert energy? chemical energy —> electrical energy
alarm clock how does a digital alarm clock convert energy? electrical energy —> sound energy AND light energy
how does a blender convert energy? electrical energy —> sound energy AND… kinetic energy
blowdryer how does a blowdryer convert energy? electrical energy —> kinetic energy in the motor AND… heat energy AND… sound energy