If you wish to reduce the stress (which is related to centripetal force) on high-speed tires, would you use large- or smalldiameter tires? Explain.

PHYS 242 BLOCK 4 NOTES Sections 27.1 to 27.7, 27.9 Consider a freely-pivoted compass needle(or a bar magnet) in the earth’s magnetic field. The magnetized object’s north pole (N-pole) points geographically north and itssouth pole (S-pole) points geographicallysouth (neither exactly so). Consideringthe earth as a magnet,currently its south magneticpole is located near its north geographic pole and vice versa (see Fig.27.3). F = q E defines the electricfield E and F = qυ × B defines the magnetic field B . This vector 0 0 equation tells us that anynon-zeroF is perpendicular toboth υ and B . Also, F is in the same direction as υ → → → × B for positive charge and oppositeυ × B for negative charge (Fig. 27.8). → The magnitude of the magnetic force F is F ⊥ |q|υB⊥s. Thus F is zero if the charged object moves paφ = 0) or antiparalle( = 180˚) to the external magnetic field (seeFig. 27.6a) and F is greatest when the object mov( = 90˚) to the external magnetic field (see Fig. 27.6c). → F is the magnetic force (in N) on the object andq is the object’s charge (in C, where 1 C≡ 1 A·s). → m → N υ is the object’s selocity (in ) and B is the external magnetA·m).eld (in T = tesla, where 1 T = 1 Cover up the solution and carefully work Example 27.1. Magnetic field lines: 1. They are used to visualize the magnetic field. 2. B is tangent to a magnetic field line at