Tham khảo tài liệu 'sat ii physics (gary graff) episode 1 part 5', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | NEWTON S LAWS OF MOTION wt The diagram above shows a block sliding down a raised plane at a constant rate. The force parallel F is the applied force the weight wt of the object acts directly toward the earth the normal force Fn acts directly out of the surface and the frictional force F opposes the motion of the block. The Fn is the result of a part of the weight being directed down the plane. FN wt sin 30 . The FN is also called the perpendicular force F and is directed from the plane into the block. Fn F wt cos 30 . The block slides down the plane at a constant rate meaning no acceleration thus no unbalanced forces are in operation down the plane. Under these conditions the force of friction equals the force parallel Fu Ff . The coefficient of friction is Al wt sin 0 sin 0 tan 0 F wt cos 0 cos 0 Peterson s CHAPTER 2 WORK AND Work ENERGY Work is defined as the product of a displacement and a force in the direction of the displacement. This translates to Work F s cos 9 When the direction of the force applied is the same as the displacement and is in the same direction as the proposed work the cos9 is cos 90 which is 1 and may be dropped from the equation. The force unit is the Newton N and displacement is in meters m . The unit of work is N m or Joule J . Work is not a vector quantity. Work is done by carrying pushing or pulling an object some distance or it may be done in lifting an object to a height against gravity. In these cases work is accomplished and is a positive quantity. Should the applied force not move the object in question no work is done or worse negative work is done imagine pushing forward against a car that is rolling backwards . The act of holding an object does not constitute the performance of work. A displacement is always required for work to be done. When a moving automobile skids along a road the road does frictional work against the tires. That is what brings the car to a stop. Work is usually mentioned with energy .
