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PHYSIC PRACTICAL

STPM 2017

ABSTACT In this experiment, we examined that the length of the string radius is directly  proportional to the period of the motion, mean that the longer the t he length of the string radius, the longer the period of the motion. To measure the period of the motion, we fixed the rotation to completed 20 oscillation. We tabulated the recorded data and illustrated the results in the form of table. We are using different length of the string radius which are 30cm, 40cm, 50cm and 60cm which to investigate the period of the motion . The graphic analysis that we use are plotting the graph to make results more visual. Graphical analysis lead to less precise result but the result commonly accepted  by the theory which the relationship between radius and period is R α T.

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PHYSIC PRACTICAL

STPM 2017

INTRODUCTION 1.1 Theory

Earlier we defined acceleration as being the change in velocity with time. Until now we have only talked about changes in the magnitude of the acceleration: the speeding up or slowing down of objects. However, since velocity is a vector, it has  both a magnitude and a direction; so another way that velocity can change is by changing its direction even while its speed remains constant. This is the type of acceleration that will be explored in this chapter. A very important case of changing direction while maintaining constant speed is called uniform circular motion. In that case, the object’s speed remains constant, hence “uniform”, while its direction is constantly changing, this is necessary to keep it moving in a circle. If there were no acceleration it would travel in a straight line. This type of motion occurs in a number of instances: important examples being the motion of the planets around the sun or the moon around the earth.

1.2 Literature review:

Uniform circular motion can be described as the motion of an object in a circle at a constant speed. As an object moves in a circle, it is constantly changing its direction. At all instances, the object is moving tangent to the circle. Since the direction of the velocity vector is the same as the direction of the object's motion, the velocity vector is directed tangent to the circle as well. The animation at the right depicts this by means of a vector arrow. An object moving in a circle is accelerating. Accelerating objects are objects which are changing their velocity - either the speed (i.e., magnitude of the velocity vector) or the direction. An object undergoing uniform circular motion is moving with a constant speed. Nonetheless, it is accelerating due to its change in direction. The direction of the acceleration is inwards. The animation at the right depicts this by means of a vector arrow. The final motion characteristic for an object undergoing uniform circular motion is the net force. The net force acting upon such an object is directed towards the center of the circle. The net force is said to be an inward or centripetal force. Without such an inward force, an object would continue in a s traight line, never deviating from its direction. Yet, with the inward net force directed perpendicular to the velocity vector, the object is always changing its direction and undergoing an inward acceleration.

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PHYSIC PRACTICAL

STPM 2017

1.3 Problem Statements

When we increase the length of the string radius, the period of the motion is different?

1.4 Objective

To study how the centripetal force which affected by the length of the string radius.

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PHYSIC PRACTICAL

STPM 2017

METHODOLOGY Manipulated variable, controlled variables and responding variable are considered in order to ensure the accuracy of the experiment. The manipulated variable for this experiment is the length of the string radius. The experiment was started by using 15cm of string and the length was then increased to 30cm, 40cm, 50cm and 60cm. There are few controlled variables in this experiment. These include the mass of the load and the mass of the rubber stopper. The responding variable of the experiment is the period of the motion. The results are recorded, tabulated and then calculated to obtain then mean of the period of the motion.

2.1 Apparatus and Materials

A few apparatus and materials were prepared for carrying up the experiment. A meter ruler, a paper clip, a rubber stopper, a stopwatch, a plastic tube, a load and also the string with length 30cm, 40cm, 50cm and 60cm.

2.2 Procedure

Diagram 1

The apparatus were set-up in diagram 1. The length of string radius was measured and cut in 30cm. The string was inserted into a plastic tube and one end of the string was connected to the load with mass 70g while another end connected to the rubber stopper with mass 30g. The paper clip was put between the end of the plastic tube and load. The stopwatch was started once the rubber stopper was rotated. The stopwatch was stopped until 20 oscillation was completed. This step was repeated 2 times to get the best result. The results was recorded and tabulated. The period of the motion was calculated. The experiment was repeated with different length of the string radius which is 40cm, 50cm and 60cm. The experiment was carrying out in no air resistance condition to ensure the accuracy of the results. The graph of T a gainst R was plotted.

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PHYSIC PRACTICAL

STPM 2017

OBSERVATION, RESULTS AND DISCUSSIONS 3.1 Observation and measurement

The period of the motion was calculated and tabulated in table below. The period of the motion was calculated by the formula, time taken to complete 20 oscillation . 20 oscillation

Length of the string radius (cm)

Time taken to completed 20 oscillation (s)

Period of the motion (s)

1

2

1

2

mean

30

14.67

14.60

0.7335

0.7300

0.7318

40

16.12

16.20

0.8060

0.8100

0.8080

50

17.94

17.83

0.8970

0.8915

0.8943

60

19.39

19.45

0.9695

0.9725

0.9710

Table 1

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PHYSIC PRACTICAL

STPM 2017

Period of Motion (s) 1.2 0.971 1

0.8943 0.808

0.8

0.7138

0.6 0.4 0.2 0 30

40

50

60 LENGTH OF THE STRING RADIUS (CM)

Graph 1 : Period of the motion against length of the string radius

3.2 Interpretation and Discussion

After the experiment has been done, the results refer to Graph 1 show that the period of the motion is getting higher by increase the length of the string radius. Thus, the longer the length of the string radius, the higher the period of the motion.

Besides that, the results we recorded in this experiment are less precise because due to the error occurred during experiment such as systematic error which is cannot  be avoided, random error which is human mistakes. It is overcome by perform repeating the experiments to obtain the secondary data in order to take the average from 2 readings, this shown to be increase the accuracy of the results and it is make sure to be consistency.

During the experiment, the fan and all the windows must be switched off to ensure the period of the motion does not affected by air resistance since the motion of oscillation quite sensitive to the surrounding condition.

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PHYSIC PRACTICAL

STPM 2017

CONCLUSION

From the results that obtained from the table and graphs, we know that the the longer the length of the string radius, the higher the period of the motion.

The value of the period of motion found in the experiments can be revised by using high standard equipment, proper setup and use digital measuring equipment in observation and measurement which will increase the accuracy of results and the obtained value will be more precise compare to theoretical value.

From this experiment, the techniques that applied are analyses equation from theory and identified the period of the motion by obtains the result from the graph. Lastly, the objective had been achieved.

This experiment helped us in better understanding the uniform circular motion in which we tried to test centripetal force and the length of the string radius affecting it.

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PHYSIC PRACTICAL

STPM 2017

REFERENCE

1) ACEAHEAD PHYSICS THIRD TERM(2013). PUBLISHED BY OXFORD FAJAR SDN.BHD

2) https://www.scribd.com/document/74409136/403-Lab-Report-Circular-Motion

3) http://www.physicsclassroom.com/mmedia/circmot/ucm.cfm

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