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GCSE Physics double award notes

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- 1. Hooke’s Law and Moments GCSE Physics
- 2. Hooke’s Law <ul><li>Page 45 </li></ul>
- 3. Learning Intentions <ul><li>By the end of the lesson we will be able to… </li></ul><ul><li>Understand the meaning of elastic and plastic behaviour </li></ul><ul><li>Investigate the relationship between force applied and the resulting extension </li></ul><ul><li>State and use Hooke’s Law to solve problems </li></ul>
- 4. Effective Forces <ul><li>Force on an object can have the following effects- </li></ul>BENDING TENSION TORSION COMPRESSION What happens to the balloon after the force is no longer applied?
- 5. Tacoma Narrows Bridge <ul><li>7 Nov 1940 Washington </li></ul>
- 6. Balloon Stretch
- 7. Elasticity and Plasticity <ul><li>All materials will behave elastically or plastically- </li></ul><ul><li>For elastic behaviour – when a force is applied the change in length is proportional to the force. The object will return to its original shape when the force is taken away. </li></ul><ul><li>For plastic behaviour – the force and the change of length are not linked. A permanent deformation occurs when the force is taken away. </li></ul>
- 8. Terminology <ul><li>Extension - change in length </li></ul><ul><li>Extended length- total length with load applied </li></ul>Force Applied Natural length Extended length Extension
- 9. Elasticity and Plasticity Elastic Limit 1. 2. Force Extension <ul><li>Elastic region (any force applied below the elastic limit) </li></ul><ul><li>Plastic region (any force applied above the elastic limit) </li></ul>
- 10. Fill out the table for the springs 4 cm 4 cm 4 cm 10 cm 2 N 4 N 6 N 10 14 18 22 0 2 4 6 0 4 8 12 Extension of spring (cm) Extended Length of spring (cm) Force Applied (N)
- 15. Hooke’s Law <ul><li>The extension of the object’s length will be proportional to the load causing that extension provided the elastic limit is not exceeded </li></ul><ul><li>E.g. if the force is doubled, the extension is doubled </li></ul>
- 16. Hooke’s Law <ul><li>If a material is loaded beyond its elastic limit then Hooke’s Law no longer applies. </li></ul><ul><li>Pg 46 </li></ul><ul><li>Q 24 - 27 </li></ul>
- 17. Learning Intentions <ul><li>By the end of the lesson we will be able to… </li></ul><ul><li>Recognise the turning effect caused by a force </li></ul><ul><li>Recall the meaning of the term ‘moment of a force’ and the moment equation </li></ul><ul><li>Use the moment equation to solve simple problems </li></ul>
- 18. Turning Effect of a Force (pg 46) <ul><li>The turning effect of a force is called a MOMENT </li></ul><ul><li>It depends on two factors- </li></ul><ul><li>1. Size of the force acting on the object </li></ul><ul><li>2. The distance the force acts from the pivot </li></ul><ul><li>The PIVOT is the point at which the rotation or turning effect occurs around (eg. The hinge of a door) </li></ul>
- 19. Turning Effect of a Force <ul><li>The greater the distance from the pivot that the force acts, the greater the turning effect </li></ul>
- 20. Levers <ul><li>Levers are any objects which experience a turning effect or MOMENT </li></ul><ul><li>There are three basic parts to the lever- </li></ul><ul><li>Fulcrum/Pivot </li></ul><ul><li>Load </li></ul><ul><li>Effort </li></ul>Pivot Effort Load Lever Moment
- 22. Turning Effect of a Force <ul><li>Draw a diagram to represent the object and mark on the pivot, the forces applied ‘load and effort’ and the distance (between the pivot and the force) </li></ul><ul><li>Wheelbarrow </li></ul><ul><li>Scissors </li></ul><ul><li>Tweezers </li></ul><ul><li>Wrench </li></ul>
- 23. Learning Intentions <ul><li>By the end of the lesson we will be able to… </li></ul><ul><li>Recognise the turning effect caused by a force </li></ul><ul><li>Recall the meaning of the term ‘moment of a force’ and the moment equation </li></ul><ul><li>Use the moment equation to solve simple problems </li></ul>
- 27. Moment Equation <ul><li>The size of the turning effect due to a force can be calculated from the formula- </li></ul><ul><li>Moment = Force x Distance (from force to pivot) </li></ul><ul><li>M = F x d </li></ul><ul><li>Nm = N x m </li></ul>Effort or Load Units A moment is a vector quantity. It has both magnitude and direction . A moment can act either in a clockwise direction or an anti-clockwise direction.
- 28. Levers can be used to… <ul><li>produce large forces from smaller ones (opening a tin of paint with a screwdriver) </li></ul>Moment = Force x (perpendicular) distance = 5 N x 0.3 m = 1.5 Nm 30cm 5N (Effort) (Clockwise Direction)
- 29. See-saw
- 30. Principle of Moments <ul><li>For a lever to be balanced… </li></ul><ul><li>the clockwise turning effect M must equal the anti-clockwise turning effect M </li></ul><ul><li>OR </li></ul><ul><li>there must be no resultant moment </li></ul><ul><li>Written as an equation- </li></ul><ul><li>M = M </li></ul><ul><li>F A x d A = F B x d B </li></ul>
- 31. Principle of Moments <ul><li>Word Equation </li></ul><ul><li>Force A x Distance A = Force B x Distance B </li></ul>d B F B F A d A
- 32. <ul><li>Practice Question </li></ul><ul><li>What force would be needed to balance the beam shown below? </li></ul><ul><li>Force A x Distance A = Force B x Distance B </li></ul><ul><li>F x 2 = 600 x 3 </li></ul><ul><li>F = 1800 / 2 </li></ul><ul><li>F = 900 N </li></ul>3m 600N F A 2m

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