Year 12 Uniform Circular Motion prac force vs period 2014

# Year 12 Uniform Circular Motion prac force vs period 2014 -...

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SACE STAGE 2 PHYSICS PRACTICAL INVESTIGATING CENTRIPETAL FORCE AND PERIOD Centripetal Force A force applied to an object in the direction of it's motion will change the speed of the object but not the direction of it's motion. A force applied to an object perpendicular to the direction of it's motion will change it's direction, but not it's speed. In both cases, the velocity is changed. In either case, the rate of change in velocity of the object is the acceleration of the object. Suppose we attach an object to the end of a string and swing it in a horizontal circle. The cord constantly pulls the object radially toward the centre of the circle. Since the pull of the cord is at all times perpendicular to the velocity of the object, the force applied to the object by the string continuously changes the direction of the motion, but not its speed. A force acting in this way, causing an object to move in a circle at constant speed is called a centripetal force . The acceleration produced by a centripetal force is called centripetal acceleration . If the cord is released, there is no more centripetal force and therefore no more centripetal acceleration and the object no longer travels in a circle but continues its motion in a straight line at a tangent to the circle at the point where the object was when the force was discontinued. Producing Centripetal Acceleration. Pass about 1.5 m of fishing line through a glass tube approximately 15 cm long. Fasten a non dangerous object such as a rubber stopper to one end of the line. Put a paper clip on the string about 1 m from the object. Hang standard masses from the free end of the string to put the string under tension and then swing the stopper around just fast enough to keep the mark on the string at the top of the tube. The weight of the slotted masses provide the centripetal force. Determine the period (time for one revolution) by a suitable method and measure the radius of the orbit. You will notice that the weight of the stopper causes the orbit to be in a plane slightly below the top of the tube; the radius of the orbit is therefore less than the length of the string. However the weight of the stopper also increases the tension in the string, and these two effects just cancel each other out. Therefore, no error is introduced by assuming that the tension in the string is equal to the suspended weight and that the radius of the orbit is equal to the length of the string.

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