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HAPPY MONDAY! •You do NOT need your folders. •If you finished Chapter 4 notes, have them on your desk. •Copy down tonight’s homework. Today, we will… •Preview week •Finish talking about energy •Talk about the concept of WORK Monday In class: Lecture notes on energy and work HW: Finish Notes Chapter 4 Tuesday In class: Lecture notes on work and machines HW: Notes on Chapter 5 due on Thursday Wednesday In class: Lab stations on simple machines HW: Finish Notes Chapter 5 Thursday In class: Lecture notes on bridges HW: Review earth science content in Grade 6 Jeopardy game Friday In class: Play Grade 6 Jeopardy HW: Review life science content in Grade 7 Jeopardy game 2/23 States of Energy • Energy can be in either of two states: – Potential – Kinetic Kinetic Energy • The energy of motion is called kinetic energy. KE = ½ mv2 • Kinetic energy depends on both mass and velocity. • The faster an object moves, the more kinetic energy it has. • So, if an object is not moving, it has NO kinetic energy. • The greater the mass of a moving object, the more kinetic energy it has. Potential Energy • Energy that is stored is called potential energy. Potential Energy ELASTIC POTENTIAL ENERGY (EPE) – energy stored in compressed springs, stretched rubber bands CHEMICAL POTENTIAL ENERGY (CPE) - energy stored in batteries, food, fuel Gravitational potential energy Gravitational Potential Energy • Energy that is stored when an object is above the ground and could fall is gravitational potential energy (GPE) • GPE depends on the weight of the object and how high it is off the ground. • Heavier objects have more GPE than light ones. • The higher an object is, the more GPE is has. Kinetic-Potential Energy Conversion Roller coasters work because of the gravitational potential energy that is built up when the cars are pulled mechanically up the tallest hill. From that point, the conversion between potential and kinetic energy powers the cars throughout the entire ride. Kinetic vs. Potential Energy At the point of maximum potential energy, the car has minimum kinetic energy, and vice versa. As one increases, the other decreases. Kinetic-Potential Energy Conversions • As the basketball is thrown into the air and gravity brings it back down, what energy conversions occur? Ball speeds up Ball slows down KE is increasing KE is decreasing PE is decreasing PE is increasing Law of Conservation of Energy: Energy cannot be created or destroyed, but it can be changed from one form to another. This means that, if you see a form of energy that wasn’t there before, it must have come from a form of energy that was already there. Like this! WORK… What is it, and why do we have to keep doing it???? To a scientist, work is the transfer of ENERGY that occurs when a force makes an object move. Work is done on an object only when a FORCE is being applied to the object and the object moves in the same direction as the force. ___ Mr. Fischer pushes the coffee cart down the hall. ___ Mr. Ranft lifts his new book about Godzilla up onto his bookshelf. ___ While holding a University of Wisconsin “Bucky Badger” statue, Ms. Pearce walks across the room. ___ Although she pushes as hard as she can, Mrs. Stolle can’t move the snack machine by the cafeteria. ___ Mrs. Hanecak stays up all night to grade some English essays. Formula for calculating work: work = force distance The SI unit for work is the JOULE (which is also the SI unit for energy) because work is the transfer of ENERGY. A person used 500 N of force to move a full wheelbarrow 30 meters. How much work was done on the wheelbarrow? A weightlifter lifts a 1,250 N barbell 2 meters. How much work was done on the barbell? A construction worker holding a 50 N brick walks 10 meters. How much work was done on the brick? Before you leave… •How does a scientist define work? •What has to be true about the motion of an object for work to be accomplished? •Give an example in which force is exerted on an object, but no work is done.