BIOLOGICAL APPLICATION A gravity board is a convenient and quick way to determine the location of the center of gravity of a person. It consists of a horizontal board supported by a fulcrum at one end and a scale at the other end. To demonstrate this in class, your physics professor calls on you to lie horizontally on the board with the top of your head directly above the fulcrum point as shown in Figure 12-33. The fulcrum is 2.00 m from the scale. In preparation for this experiment, you had accurately weighed yourself and determined your mass to be 70.0 kg. When you are at rest on the gravity board, the scale advances 250 N beyond its reading when the board is there by itself. Use this data to determine the location of your center of gravity relative to your feet. SSM
Physics Week 8 Chapter 26: Direct Current Circuits Kirchhoff’s Law 1 (Voltage Law) In a closed conducting path, the sum of potential differences is zero ΣV = 0 Ɛ = V 1 V + 2 3 - Ɛ + V 1 V + 2 = 0 3 Kirchhoff’s Law 2 (Current Law) Sum of currents entering is equal to the sum of currents leaving in a circuit junction ΣI = 0 Resistors in Series R eqR + 1 + R 2 3 I is the same through each resistor V is different for each resistor I Req IR + 1R + IR2 3 Ɛ = V 1 V + 2 3 Resistors in Parallel 1/ R eq1/R + 1/R + 1/2 3 I is different through each resistor V is the same for each resistor I = I1+ I 2 I 3 Ɛ / Req Ɛ /R + 1 /R + Ɛ2/R 3 Open Switch – t /RC q = c Ɛ (1-e ) – t /RC I = Ɛ/R e Closed Switch
