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# Download Chapter 4 – Work and Machines

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Chapter 8 – Work and Energy 8. 1 Work pp. 188-192 TERMS TO LEARN Work – the action that results when a force causes an object to move in the direction of the force being applied Joule – the SI unit of work JAMES PRESCOTT JOULE An English physicist The SI unit of work (the joule) is named after him 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. WORK The scientific meaning of work is that work is done on an object: only when a force makes an object move in the direction of the force AND only when the force is being applied to the object. CALCULATING WORK The equation you use to calculate work is: work = force × distance W=F×d The SI unit of work is the joule (J) 1 J=1N·m 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 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. 8.1 Work Complete Skill Sheet 8.1 Work