Energy

10/2/14   What  is  energy?   ENERGY   — Energy  is  the  ability  to  do  work  (cause   change).   — When  a  force  causes  an  object  to  be   displaced,  work  was  done  upon  the   object.   — Examples:    brushing  your  hair,  walking   down  the  hall,  eating  your  lunch,   yawning.       What  are  different  forms  of  energy?   Kinetic  Energy   — Energy  in  the  form  of  motion.   — Depends  on  mass  and  velocity   (similar  to  momentum)   — Examples:    spinning  bicycle  wheel,   a  car  driving         Calculating  Kinetic  Energy   Let’s  Practice!   — Kinetic  energy  =  ½  mass  x   — A  15-­‐kg  bicycle  carrying  a  50-­‐kg  boy  is  traveling  at   — ↑mass  =  ↑  kinetic  energy   — The  kinetic  energy  of  a  boat  is  calculated  at  52,000   velocity2   — KE  =  ½  m  x  v2   ↑  velocity  =  ↑  kinetic  energy   — If  you  double  the  velocity,  the   energy  quadruples.   a  speed  of  5  m/s.    What  is  the  kinetic  energy  of   the  bicycle  (including  the  boy)?   — 812.5  Joules  (J)   J.    If  the  boat  has  a  mass  of  39,000  kg,  with  what   velocity  is  it  moving?   — 1.63  m/s   — Joule   ¡Mass  =  kg;  velocity  =  m/s   1   10/2/14   Potential  Energy   Elastic  Potential  Energy   — Potential  energy  =  stored  energy   —Energy  stored  by  something   due  to  position   — Examples:    an  apple  hanging  in  a   tree;  a  book  on  a  shelf     that  can  stretch  or  compress   —Examples:    a  rubberband  or  a   spring     Chemical  Potential  Energy   Gravitational  Potential  Energy   —Energy  stored  in  chemical   —Energy  stored  in  objects  above   bonds  between  atoms   —Examples:    Food,  gasoline   Earth’s  surface.   —GPE  =  m  x  9.8  m/s2  x  h     — Mass  –  kg,  height  -­‐  meters     — (↑  h  =  ↑  GPE)   — measured  in  joules   More  Practice!   Let’s  Review  KE  and  PE   — A  0.06-­‐kg  tennis  ball  starts  to  fall  from  a  height  of   — How  are  kinetic  energy  and  potential  energy   2.9  m.    How  much  gravitational  potential  energy   does  the  ball  have  at  that  height?   — 1.7  J   — An  object  of  mass  10  kg  is  raised  through  a  certain   height.  Its  potential  energy  is  increased  by  1960   Joules.  Find  the  height  of  the  object  initially.   different?   — What  are  the  three  types  of  potential  energy?   — How  are  elastic  potential  energy  and  chemical   potential  energy  different?   — 20  m   2   10/2/14   Conservation  of  Energy   Conversions   — Energy  is  not  lost  or  gained;  it  changes   form.   — Transforming  Energy   — Often  electrical  energy  is  converted  to  light  and   thermal  energy   ¡ Examples:    light  bulb,  alarm  clock,  curling  iron,   computers   — Chemical  energy  is  usually  converted  to  kinetic   energy  or  thermal  energy.   ¡ Examples:    Your  body,  food,  vehicles   Falling  Objects   Potential   Kinetic   Potential   Mechanical  energy  (ME)  =  potential   energy  (PE)  +  kinetic  energy  (KE)   Swinging  Energy   — 100%  PE   0%  KE       — Falling  =  change     from  PE  to  KE       — Ground:    0%  PE                  100%  KE   Conservation  of  Energy   — Energy  cannot  be  created  or  destroyed,  ONLY   transferred  from  one  to  another…..   3   10/2/14   Finding  Energy  Transformations   — Friction:  seems  like  energy  is  disappearing,  but  it   is  actually  converted  into  different  energies,  such   as  thermal  energy.       — Mass  into  Energy:  Nuclear  fusion  is  an  example.     Remember  e=mc2.    A  little  mass  =  a  lot  of  energy   — Two  hydrogen  nuclei  come  together  and  combine  to   form  one  helium     — Nuclear  Fission:    Kinetic  Energy  to  thermal   Energy  Conversions  in  Your  Body   — Chemical  energy  to  kinetic  and  thermal  energy.   — Stores  energy  as  fat,  example  of  potential  energy   — Also  converts  to  heat  and  use  this  energy  to  move   — Maintaining  Healthy  Weight   — Must  have  proper  balance  between  energy  contained   in  food  eaten  and  energy  body  uses   energy   — Mass  into  energy  again!   — Nuclei  broken  apart…  ENORMOUS  energy     4