Get in your groups, you guys will teach each other your concepts, review ! Work, Power and Energy Jigsaw Activity Video Clips on Work, Power and Energy df89eb/work-energy-power df89eb/work-energy-power Work The product of displacement and the force in the direction of displacement Only force component along the displacement contributes to the work being done W = F( x) Sample Problem A warehouse worker is moving a large box with an area of 10 m2. If the woman pushes on the box with 120 N of force and is able to move the box 3 meters towards the right, how much work is being done? If she was to then load the crate on a pellet-mover and pull the crate with the same force holding a handle at 39 o, how much work did she do now if she moved it the same distance? Energy (Joule) Many forms of energy exist. Can you name some? You may associate energy with motion. Is this an accurate assumption? Law of Conservation of Energy. Say what? There is a relationship between work and energy. What is the relationship? If you perform work on an object, you can increase its kinetic energy! Water moving a turbine in a dam! Kinetic Energy Energy of objects in motion Equals one-half the mass of the object times the square of its speed. What would increase the kinetic energy of an object? With kinetic energy, only the magnitude of the velocity matters. Not direction. Work-Kinetic Energy Theorem Stationary objects will remain stationary unless work is done. Once the object is in motion, it has kinetic energy! Thus, the change in its energy must equal the work done on the system! Net work equals the change in kinetic energy! Positive work on an object increases its Kinetic Energy. When, then, would negative work occur? Sample Problem You are a soccer player on the field of a really important game! The soccer ball is regulation at a mass of 420 g. If you apply a small force of 240 N with the side of your foot to pass the ball to your partner next to you and move the ball 0.2 m, how fast should the ball move? Power Rate of work Work divided by time Rate of which energy is consumed/output One reason we care about power is because more power means we can accomplish work faster ! Would you rather have a car that goes from 0 to 60 in 2 seconds or two minutes? Units of Power Unit for Work? Unit for Time? Sometimes, power is expressed in terms of horsepower. Old standard How much work a horse could do in a certain amount of time Why would they do this? What other equations do we have for power? Sample Problem Applying a force of 200,000 N, a tugboat pulls an oceanliner from the docks out to port in 22 minutes. What is the tugboats average power (assuming it pulled the oceanliner in a perfectly straight line)? Potential Energy Energy related to the positions of and forces between the objects that make up a system Energy of no motion Gravitational potential energy; increases with height of object to ground What factors would impact gravitational potential energy? Sample Problem A window-washer is 25 meters in the air cleaning windows on a skyscraper. If he has a weight of 750 N, how much potential energy does he have stored? If the cable snapped, and he came crashing to earth, what kinetic energy would he possess upon hitting the ground? Relationship between PE and KE Law of Conservation of Energy Total energy = PE + KE What does this mean?