Transcript Review - ND
Circular Motion • Explain what causes and object to move in uniform circular motion. An object’s inertia makes it try to move in a straight line. An unbalanced force towards the center of the circle forces it to move in a circular path. What is the other name given to the centripetal force shown in the diagram at left? Tension What will happen if the boy turns the ball through the circle at an extremely high rate? The required centripetal force will exceed the tension that the string can provide, and the string will break. Circular motion A 30.0 g ball is connected to the roof, and then sent into uniform circular motion. a) Draw a free body diagram of the forces FT FG b) If the ball is moving at 10 m/s in a circle which has a 45 cm radius, what is the centripetal force? Fcent sin 6.667 FT = sin 25 FT = 15.8 N c) What is the tension in the rope if Q = 250 F = T FT FG Fcent sin = Fcent FT Fcent Fcent Fcent mv 2 = r (0.030)(10) 2 = 0.45 = 6.67 N Centripetal force – ratio comparisons Fcent mv 2 = r If the speed of an object is tripled, how much more centripetal force will be required to keep it moving in circular motion? 9 times as much centripetal force If the mass of the object is tripled, and the radius of the curve is twice as great what will happened to the required centripetal force? 1.5 times as great The mass and velocity of the object are both tripled, and the radius of the circle is decreased to 1/3 of what it was, how will the new required centripetal force compare to the old one? 81 times as great Kepler’s Laws • A comet that was last seen in 1978 has an average mean distance of 5.57 times the earth’s distance from the sun. When will the comet be seen next? rA3 TA2 = 2 3 rB TB Tcomet = Tcomet = 3 2 rcomet Tearth 3 rearth 1978 + 13.1 x 3 = 2017 The comet will be next seen in 2017 Return to day 8 (5.57R E )3 (1) 2 R E3 Tcomet = (5.57)3 Tcomet = 13.1 a