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Work Done by Forces

What can you remember from P3 in year 11? Definition Formula Derived Units Actual units. Work Done by Forces. Learning Objectives :. Work Done. To understand how to calculate the work done by a force. To understand how WD can be extended from GCSE to AS. Book Reference : Pages 148-150.

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Work Done by Forces

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  1. What can you remember from P3 in year 11? • Definition • Formula • Derived Units • Actual units Work Done by Forces

  2. Learning Objectives : Work Done • To understand how to calculate the work done by a force. • To understand how WD can be extended from GCSE to AS Book Reference : Pages 148-150

  3. Definition : Work is done on an object when a force acting on it makes it move Formula : Work done = force x distance moved in the direction of the force Units: Derived : N x m = Nm called Joules (capital J) Work Done

  4. 1 Joule is the amount of work done when a force of 1N moves an object through 1m This is the amount of work required to lift a typical apple, (which weighs 1N) through 1 metre! Work Done

  5. Joule is the unit associated with energy.... We’ve seen from year 7, 9 and beyond that energy can never be created or destroyed only converted/transferred If we do 1J of work raising our apple against gravity where has this one Joule of work gone? We cannot simply lose 1J of energy! Work Done

  6. Since we have raised the height of the apple, we have raised the gravitational potential energy of the apple by 1J (PE = mgh) Many work done problems involve lifting masses.... A common mistake is forgetting to convert the mass to a weight since we need a force not a mass (Weight = mg) Work Done

  7. How can we further complicate WD to take it beyond GCSE to AS? Look back at the exact definition of “distance” in the WD formula... “distance moved in the direction of the force” We can make things more interesting by having the force at an angle to the resulting motion.... Work Done

  8. A suitable example would be a yacht being moved by a wind which blows at an angle to the direction of motion. We can use our new resolving skills to work out, (via trigonometry) to how much of the force is “moved in the direction of the force” Work Done

  9. The second way in which WD can be extended for AS is to apply it to Hooke’s Law.... (Stretching a spring in a uniform fashion without damaging it) We’ll revisit this when we tackle the “materials” part of unit 2 Work Done

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