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Nuffield Free-Standing Mathematics Activity Investigating friction

Nuffield Free-Standing Mathematics Activity Investigating friction. Investigating friction. Why doesn’t the climber slide down the rock? What forces could be helping to keep her in this position?. Push. Investigating friction. Heavy package. Think about:.

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Nuffield Free-Standing Mathematics Activity Investigating friction

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  1. Nuffield Free-Standing Mathematics ActivityInvestigating friction

  2. Investigating friction Why doesn’t the climber slide down the rock? What forces could be helping to keep her in this position?

  3. Push Investigating friction Heavy package Think about: Why will a very small push not move the object? What happens as the force of the push is increased? What factors do you think influence a friction force?

  4. Observe Define problem The modelling cycle Real world Mathematics Set up a model Analyse Validate Interpret Predict

  5. hanger and masses pulley and clamp wooden block(s) or elastoscale Investigating friction You need: books Investigate your ideas

  6. Horizontal pull, P Think about:How do you think the friction force, F, varies with an increasing pulling force, P? F Sketch a graph Think about: How does the shape of the graph alter as the mass of the book is increased? 0 P

  7. This practical apparatus may help your investigation … or use an elastoscale … Mass M Investigate how the maximum friction force, FMAX,varies with the normal contact force, N Vary N by using different masses M

  8. Plot a graph showing how limiting friction, FMAX varies with normal contact force, N. FMAX 0 N Think about: Is FMAX = constant Na good model for friction?

  9. N P F mg P Modelling friction – Summary F ≤ mN whereFis the friction,Nis the normal contact force andmis a constant called the coefficient of friction Pis gradually increased until sliding occurs Force diagram • Facts tangentially along the two surfaces • Facts in a direction to oppose motion maintains equilibrium • Before slidingF = P • There is a maximum friction force,FMAX • Psliding= FMAX • When sliding is taking placeP FMAX

  10. F FMAX N 0 P F P mg Modelling friction – Summary Graph of F against P no sliding sliding - dynamic - static When the bodies are not moving F ≤ mN When the bodies are moving F = mN Psliding

  11. Reflect on your work Think about how friction is used in everyday life. For example, could you walk if there were no friction force? Would your shoelaces stay tied up? Could you carry something on a tray if there were no friction? Can you suggest how friction could be increased or decreased in any of the examples? If you had graphs of FMAX plotted against N for different pairs of materials in contact, how could you tell which combination of materials had the highest coefficient of friction?

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