CAN YOU SLING IT? Materials: Rubber band, nickel, ruler Procedure: 1. Using two fingers carefully stretch a rubber band on the lab desk so there is no slack. 2. Place a nickel on the table slightly touching the midpoint of the rubber band. 3. Push the nickel back so that one edge of the rubber band is halfway the distance to the other and release. Measure the distance the nickel travels with your ruler in centimeters. 4. Push the nickel back so the one edge of the rubber band touches the other side of the rubber band and release. Measure the distance the nickel travels with your ruler in centimeters.
CAN YOU SLING IT? Answer the two Analysis questions. Due Monday.
TYPES OF ENERGY Kinetic energy Potential energy Thermal energy Chemical energy Nuclear energy Electrical energy Mechanical energy
TYPES OF ENERGY o Thermal energy - due to temperature (this comes from the motion of molecules, so it is really kinetic energy) o Chemical Potential Energy - stored in chemical bonds o Nuclear energy - stored in the nucleus of an atom o Electrical energy – electromagnetic (EM) interactions
ENERGY Energy is the capacity (ability) to do work. Kinetic Energy: Associated with an object in motion. Potential Energy: Present in an object that has the potential to move because of its position. Kinetic and Potential Energy
KINETIC ENERGY, KE Energy of Motion KE of an object depends upon two variables: 1. the mass (m) of the object 2. the speed (v) of the object.
KINETIC ENERGY Calculating Kinetic Energy A formula to find the kinetic energy of any body based on its velocity.
POTENTIAL ENERGY, PE An object can store energy as the result of its position.
TYPES OF POTENTIAL ENERGY Gravitational Potential Energy – energy stored in an object because of its position above the earth. Elastic Potential Energy – energy that is stored in something stretchy Chemical Potential Energy – energy that is stored in the bonds of atoms and molecules.
GRAVITATIONAL POTENTIAL ENERGY GPE is the energy stored in an object as the result of its vertical position (i.e., height). Amount of GPE is dependent on two variables: 1. the mass 2. the height above ground
GRAVITATIONAL POTENTIAL ENERGY GPE = mgh m = mass g = 9.8m/s 2 h = height above ground
ELASTIC POTENTIAL ENERGY Elastic PE is the energy stored in elastic materials as the result of their stretching or compressing.
CHEMICAL POTENTIAL ENERGY a form of potential energy that can be absorbed or released during a chemical reaction. It may also change during a phase change like melting.
CONSERVATION OF ENERGY Energy cannot be created or destroyed…only changed from one form to another. The total energy of an isolated system remains constant (isolated systems have no external forces and no mass changes)
CONSERVATION OF ENERGY ENERGY BEFORE = ENERGY AFTER Energy can be changed from one form to another, but it does not disappear
MECHANICAL ENERGY, ME The motion of some objects contain a combination of only kinetic and potential energies. ME is the sum of the KE and forms of PE associated with a system Therefore, ME= KE + PE
TOTAL ENERGY OF THE SYSTEM REMAINS THE SAME Conservation of Energy
CONSERVATION OF MECHANICAL ENERGY Therefore, ME i = ME f KE i + PE i = KE f + PE f ½ mv i 2 + mgh i = ½ mv f 2 + mgh f
CONSERVATION OF MECHANICAL ENERGY Conservation of ME only holds true when the only energies of the system are KE and PE. Therefore, in the presence of friction, energy is transformed to other types of energies.
ENERGY CONVERSION When one type of energy is changed or transformed into another type of energy.
WHAT ABOUT A FALLING OBJECT? What happens when it hits the ground? Where did the energy all go?
ENERGY CONVERSIONS OF A DROPPED OBJECT As it is falling and when the object hits the ground, the energy is converted into other types of energy such as: sound energy (waves) light Energy (sparks) thermal energy due to friction (heat) in the ground and air vibrations in the earth (energy waves.) If the object bounces, some energy is converted momentarily into elastic potential energy.
EOCT QUESTION Which statement about energy is true? A. Energy can be increased in a closed system. B. Energy cannot be conserved. C. Energy can be decreased in a closed system. D. Energy cannot be created nor destroyed.
TO DO Work the Kinetic Nergy and Potential Energy Practice