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Transcript

WORK 8.1 Chapter Eight: Work 8.1 Work 8.2 Efficiency and Power Chapter 8.1 Learning Goals Tell what it means to “do work” in a scientific sense. Apply an equation to determine the amount of work done by a force. Infer that work requires energy. Investigation 8A Manipulating Forces Key Question: How do simple machines work? 8.1 Work In science, work is a form of energy you either use or get when a force is applied over a distance. You do 1 joule of work if you push with a force of 1 newton for a distance of 1 meter. 8.1 Work When thinking about work, remember that work is done by forces that cause movement. If nothing moves (distance is zero), then no work is done. 8.1 Work Force (N) Work (joules) W=Fxd Distance (m) 8.1 Work and energy Doing work always means transferring energy. The energy may be transferred to the object you apply the force to, or it may go somewhere else. 8.1 Work and energy You can do work to increase an object’s potential energy. Then the potential energy can be converted to kinetic energy. 8.1 Work A raised object’s potential energy equals the amount of work it can do as it moves down. The amount of kinetic energy an object has equals the amount of work the object can do by exerting force as it stops. 8.1 Work If force is equivalent to the weight of the object in newtons, and height (h) is equivalent to distance (d), Then multiplying the weight by height gives you the amount of work the object can accomplish as it moves down (as well as its potential energy). 8.1 Work Force A does no work because it does not cause the block to move. Force B is applied at an angle to the direction of motion, so only part of force B does work. The most effective force to move the block is force C. Solving Problems How much work is done by a person who pulls a cart with a force of 50 newtons if the cart moves 20 meters in the direction of the force? Solving Problems 1. Looking for: …work done by person 2. Given: …force = 50 N (forward); …distance = 20 m 3. Relationships: Work = force x distance 4. Solution 50 N × 20 m = 1,000 joules.