I will be taking part in an experiment where I will be investigating the time taken for a pendulum to complete 20 swings while altering the length of the string.PlanningSafetyWhen taking parts in experiments like these there are a number of things that can go wrong and be harmful to personal safety, therefore, I will state and explain all of the safety precautions you should take when carrying out this type of experiment. This is a physical experiment not a chemical experiment so in theory there shouldn’t be much that can go wrong. I would suggest the only safety hazard would be if the apparatus was left on the side of a bench, therefore to overcome this I will make sure that all of my equipment is set up in the centre of the bench so that nothing gets knocked over which could ruin the experiment or even more importantly hurt yourself.Fair TestIt is important to make an experiment like this as fair as possible. It will never be possible in the environment we are given with to make this completely fair however we can try to make it as fair as possible. In order to do this the following will have to be done,* The weight of the pendulum must not be altered at all because the idea of this experiment is to see if the length of the string affects the total time, not the weight.
If the weight of the ball on the end of the string changed at any point during the experiment it would be an unfair test meaning that the results would not be accurate.* Somebody will have to monitor how many swings have been done and another person will have to be in charge of a stop clock to time the event. It is very important that some one monitors the swings closely so that they can tell the person in charge of the stop clock exactly when to stop.* The experiment must be taken place in a controlled environment, by this I mean it must be done in the same room once started. It cannot be done outside or where there is a draft otherwise the swing time and environment becomes unreliable making it an unfair test.ApparatusFor this experiment a number of apparatus will be used, these are,* String – This will be used as the main variable of the experiment, this is what will determine the outcome of my conclusion* Pendulum Ball – This will be made from plaster scene and regularly checked for weight as it’s a changeable product.
* Clamp Rod – This will be used to attach the string from so that the pendulum can swing with ease.* Stop Clock – This will be used to time the experiment, the clock will start as soon as the pendulum is released and as soon as the pendulum reaches 20 swings.* Ruler – This will be used to make sure that the pendulum has completed a full swing so that the test can be as fair as possible.I intend to carry out this experiment 3 times but on each length of string.
I will be using 10 different lengths of string; this is so that I can gain a predicted and accurate result table. I predict that the length of the string will affect the time taken for 20 swings, this is because:h0 = maximum heightv0 = maximum speedGravitational Potential Energy (GPE)GPE = mghm = mass of object (kg)g = gravitational field strength (10 N/kg)h = vertical height of object (m)GPE (J)Kinetic Energy (KE)KE = 1/2mv2v = speed of object (m/s)KE (J)At the top of the swing the potential energy is a maximum and the kinetic energy is zero. At the bottom of the swing the potential energy is zero and the kinetic energy is a maximum. So, all the potential energy is transferred to kinetic energy by the time the bob has reached the bottom of the swing. This follows from the Law of Conservation of Energy which states that energy can not be created or destroyed, only transferred from one type to another.
ObtainingHere are my results:Length Of String (cm)Mass (g)1st2nd3rdAverageTime (s)1096.5g14.1214.2214.3314.220.712095.5g19.
7842.6542.0042.012.10As you can see from my results my prediction was correct. The longer the string, the more time it will take for the pendulum to complete 20 swings, however, to confirm this I will now analyse my results.
AnalysisAnalysing results in different formats is very different because it is more reliable and shows clearly what has happened. I have made a Bar Chart and a Line Graph to show these results.As you can see easily from this bar chart the length of the string affects the time taken for 20 complete swings. Here is a line graph to show the same thing.Once again as you can see from this graph it clearly shows that the time taken increases when the string length increases. My prediction was correct and through recording these results and analysing them it has been confirmed. I will now evaluate this coursework.
ConclusionI have been able to prove that the longer the string gets, the more time it will take to complete the desired amount of swings. It seems likely that the same trend would continue if the string was made longer. Shorter lengths look like they would also follow the same pattern although it gets more difficult to take the measurements as the time gets shorter. For very short lengths the trend may not continue and would be very difficult to measure. It is not possible to try lengths shorter than the diameter of the bob, for instance.
A much smaller bob on a very fine and lightweight filament could be made and tested.EvaluationReliabilityNo significant problems or difficulties were encountered when carrying out this investigation. The accuracy and reliability of the results and conclusions are very good.ImprovementsThe procedure used was simple and straightforward and no difficulties were encountered. A small improvement could be made to measuring the length of the pendulum.
A longer ruler, or piece of wood, could be placed level with the point of suspension, and a set square could be placed along the flat side and just touching the bottom of the pendulum. This distance could then be measured more accurately than trying to guess where the middle of the bob is. The thread used was quite stretchy. If the investigation was repeated I would replace it with something more rigid, such as extra strong piece of string.
More repeats could be taken but I don’t think this would add much to the accuracy of the conclusions. Overall this has been a fun and educational experiment; I would quite enjoy doing it again,