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Presentation On Circular Motion, Turning Effects Of Forces And Centre Of Gravity

Home > PowerPoint Slides > Presentation On Circular Motion, Turning Effects Of Forces And Centre Of Gravity
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This PPT is suitable for the IGCSE and O Level Physics students. It only provides theoretical background of the topic. The practice questions, worksheets and topical questions will be discussed during the tutoring sessions

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  1. Circular Motion, Turning Effects of Forces and Centre of Gravity Physics (IGCSE / O-Level)
  2. What will you learn in this lesson? • Motion in circular path due to force • Relation of the force with speed, radius and mass of the circular path • Moment of a force as a measure of its turning effect with everyday examples • Apply the principle of moments to situations with one force each side of the pivot or more than one force each side of the pivot • Equilibrium • Centre of gravity • Determine the position of the centre of gravity of an irregularly shaped plane lamina • The effect of the position of the centre of gravity on the stability of simple objects
  3. Circular Motion path ot apple when string breaks lift gravity pull ot gravity For an object following a circular path, the object is acted on by a force at right angles to its velocity. The force that keeps an object moving in a circle always acts towards the center of the circle. If the force disappears, the object will move off at a tangent to the circle; it will not fly outwards, away from the center.
  4. Circular Motion (contd.) The resultant force will act towards the center of circle because of acceleration. It also depends on the object's mass, speed and radius of motion A bigger force is needed, if: 1. The object's mass is bigger (speed and radius are constant) 2. The object's speed is bigger (mass and radius are constant) 3. The object's radius of motion is smaller (speed and mass are constant) Speed is constant but velocity is changing due to change in direction
  5. Turning Effect Turning effect causes an object to rotate or turn when the force is applied First of all, look for the pivot — the fixed point about which the object will turn. Now push with as big a force as possible, and as far as possible from the pivot — at the other edge. To have a big turning effect, the object must be pushed hard at right angles to the surface. Pushing at a different angle gives a smaller turning effect. Turning effect of a force about its pivot is called moment
  6. Equilibrium Equilibrium always means that two or more things are balanced. If an object is in equilibrium: • the forces on it must be balanced (no resultant force) • the turning effects of the forces on it must also be balanced (no resultant turning effect)
  7. Moment • The moment of a force is bigger if the force is bigger. • The moment of a force is bigger if it acts further from the pivot. • The moment of a force is greatest if it acts at 900 to the object it acts on. weight of girl father's push A see-saw is an example ot a beam, a long, rigid object that is pivoted at a point The girl's weight is making the beam tip one way. The father's push is making it tip the other way. It the beam is to be balanced, the moments ot the two forces must cancel each other out.
  8. Calculating Moment moment of a force = force x perpendicular distance from the Pivot beam pivot moment of force 40 N x 2.0 m = 80 N m The unit of moment is Nm. If distances are given in cm, the unit of moment will be N cm. Take care not to mix these different units (N m and N cm) in a single calculation.
  9. Principle of Moments The we'ght of the girl will cause anti-clockwise moment The force applied by father will cause clockwise moment When an object is balanced, the sum of anti-clockwise moments about any point is equal to the sum of clockwise moments about that same point total clockwise moment = total anticlockwise moment antiClockwise moment = 500x20= 1000 N m clockwisemoments — (300x2.0) + (400 x 1.0) = 600Nm+400 N m — IOOONm
  10. Principle of Moments (contd.) The beams are balanced, find the forces F osm osm 20 N 1.0m ION
  11. In Equilibrium Lets take an example of see-saw. If weights of the kids and weight of the see-saw (200 N) were the only forces acting, they would make the see-saw accelerate downwards. Another force acts to prevent this from happening. There is an upward contact force where the see-saw sits on the pivot. = 1400K Contact force = (500 + 200 + 400 + 300) N = 1400 N Now we have satisfied the two conditions that must be met if an object is to be in equilibrium: there must be no resultant force acting on it total clockwise moment = total anticlockwise moment.
  12. Centre of mass The arrows in above images show all of their masses (or weights) are concentrated at this point, known as the centre of mass. The centre of mass is in the middle of the body, roughly level with the navel. A ball is much more symmetrical, and its centre of mass is at its centre. For an object to be stable, it should have a low centre of mass and a wide base. Pyramid is an example of this
  13. Centre of Mass and Stability An object will topple-over if its center of gravity passes outside its base very (b) Figure 5
  14. Centre of Mass and Stability (contd.) Explain how the high-wire artists remain stable on the rope? Why a tall glass is unstable? Where will the centre of mass lie?
  15. Centre of Mass and Stability (contd.) How to find the centre of mass of an irregular surface? Video: https://www.voutube.com/watch?v=piK 3RuiCXk 090 o

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