Transcript Energy
Energy NASA What is energy? Your textbook defines energy as the ability to make something happen… Teachengineering.com Vital Imagery, Itd More precisely in physics energy is the ability to do work… Energy of Motion Mechanical Energy Other forms of energy Potential Energy Stored energy… Energy can be transformed from one type to another… Electrical Light Thermal Energy can be transferred from one object to another…. Practice identifying energy transformations… …as a class powerpoint… …as individuals worksheet… Lets look specifically at the energy of motion… farnes.com Mechanical Energy …the energy of motion Mechanical Energy ME = PE + KE Potential Energy Kinetic Energy PE KE Gravitational Potential Energy …the potential energy that an object has because it is high up above the ground. Gravitational Potential Energy Height MASS Weight g (acceleration of gravity) Which has more potential energy: a 5-kilogram pumpkin that is 1 m above the ground or a 1-kilogram pumpkin that is 1 m above the ground? Explain. The pumpkins are both at the same height above the ground. Therefore the 5 kg pumpkin has more gravitational potential energy because it has more mass. Which has more potential energy: a 5-kilogram pumpkin that is 1 m above the ground or a 5kilogram pumpkin that is 10 m above the ground? Explain. Both pumpkins have equal mass. Therefore the pumpkin that is 10 meters above the ground has more gravitational potential energy because it is higher. Gravitational Potential Energy PEgrav Unit for Energy joules (J) C H Jeaens, Nature, 26, 616 (1882) Kinetic Energy Anything that is moving has kinetic energy Kinetic Energy Speed (velocity) Mass Which has more kinetic energy: a Matchbox™ car that is moving at 5 m/s or a real car that is moving at 5 m/s? Explain. Both cars are moving at the same speed. The real car, however, has more mass and therefore has more kinetic energy. Which has more kinetic energy: a 15 kg child that is walking at 1 m/s or a 15 kg child who is running at 3 m/s? Explain. Both children have the same mass. The child who is running at 3 m/s therefore has more kinetic energy because he/she is running faster. Bouncing Ball Hig hPE Low KE Hig hPE Hig Low hPE KE Low KE Low PE Low PE Hig hKE Hig hKE PE KE As we have already seen… What about friction? CONSERVATION OF ENERGY!!!! The Law of Conservation of Energy Energy can neither be created nor destroyed… …but may be transferred from one object to another and transformed from one type to another. Apply conservation of energy to motion PE KE At which point would the roller coaster have the most potential energy? The roller coaster would have the most gravitational potential energy at point A because it is the highest above the ground. At which point would the roller coaster have the most kinetic energy? The coaster would have the most kinetic energy at point B. All of the potential energy has been transformed into kinetic energy and the coaster is moving the fastest at this point. At which point would the roller coaster be moving the fastest? The coaster will be moving the fastest at point B Why does the first hill have to be the highest? In the real world…there is FRICTION!!! Some of the mechanical energy transforms in to thermal energy through friction -heating up the track… With less mechanical energy, the car can only rise to heights lower than the first hill. KE and PE of a roller coaster http://www.hkphy.org/oceanpark/rol/resource/rollercoaster_e.ht ml Roller Coaster (link on website) How can we reach the top of the first hill? Must somehow add total mechanical energy to the system. We do this in the form of “work.” Why do roller coasters eventually stop? Must transfer mechanical energy from the coaster to the track… …usually friction transforms mechanical energy to thermal energy. …the coaster transfers energy to the track….the track heats up…and the coaster slows down… Today’s Activity: Small Group Presentations of PE KE explorecrete.com (Bungee.gr) Freshpowder.com Squaw Valley Olympic Photos geewocka Let’s look at an example… • Draw a picture • Make charts of KE, PE, and total ME for 45 locations on picture • Present to class describing changes in KE, PE, and ME • Watch video and provide commentary… Roller Coaster – Draw a Picture (on larger whiteboard) Draw KE, PE, and ME Charts (use small whiteboards) Watch video and provide commentary Your turn to consider other examples where energy transforms between kinetic energy and potential energy. Bridge swinging The Skatepark Bungee jumping (giant spring) Ski-jumping Linerider See class website for a link to this game…where you can create your own roller coaster.. Also on website…link to Phet physics animations… Phun – also on website