Pendulum Investigation Noadswood Science, 2013

Pendulum Investigation Your task is to investigate different pendulums, finding out which factors affect the way they swing As you complete this experiment you need to think how you can make this test a fair one, how you can be accurate and precise, and how you can ensure the results are reliable Sunday, January 31, 2016

Initial Questions Initially you need to brainstorm what affects how a pendulum swings? What parts make up a pendulum What scientific processes take place when it swings Why does a pendulum swing What determines how fast the pendulum swings, and at what trajectory the pendulum follows Draw a basic diagram of the pendulum, listing all the apparatus needed for it A pendulum consists of a mass (or bob) attached to a pivot, from which it can swing freely

Initial Questions Every moving object has kinetic energy - the more mass an object has and the faster it is moving, the more kinetic energy it has A pendulum is a simple machine for transferring gravitational potential energy into kinetic energy, and back again… A pendulum’s swing speed and trajectory are determined by how the pendulum is set up – this is what you are investigating!

Demo Look at the demo of the pendulum Consider what variables affect the pendulum Determine which factor(s) you could test for - what is your independent variable (what you change), and what is your dependent variable (changed by the experiment) What control variables will you have to monitor?

Introduction Initially write you introduction for the pendulum investigation Note your aim (what we are doing); why we are doing it and what tests which will carry out and why What affects the swing of a pendulum: – Mass of bob? Length of string? Surface area / shape of bob? Angle of release? Atmospheric conditions (temperature / pressure / wind etc…)?

Method Once you have decided what factors you think affect the swing of a pendulum you need to identify how you can measure these effects For example you could set up your pendulum and measure the time taken for 10 swings to take place / how many swings there are in 1 minute etc… You could then change your variable, and record the new time Length of string (cm) Number of swings in 10 seconds 5123Average 10 Etc…

Measurements You need to measure the length of the string from the pivot to the middle of the bob Length of string from pivot to middle of bob

Measurements When you add a greater mass to the bob of the pendulum (with plasticine) ensure you try and keep the shape of this bob the same Ensure the bob is always the same shape

Results - Mass Mass of bob (g) Number of swings in 30 seconds 1123Average etc…

Results - Length Length of string (cm) Number of swings in 30 seconds 1123Average etc…

Experiment You have this lesson to complete your experiments Remember to be as accurate and precise as possible, repeating an appropriate amount of times and recording your results You will also need to calculate all the averages this lesson for your results

Conclusions Your task is to graph your results – one graph for the mass and one for the length changes A scatter graph is most suitable – mass of bob / length of string on the x axis, and number of swings in 30 seconds on the y axis Remember to add a title; units etc… Once you have drawn your graphs you need to complete an analysis – what do the results show you / why do you think this is?

Graph Hopefully you have found that the mass of the pendulum does not affect the number of swings it will make in a given time

Graph Hopefully you have found that the length of the string affects the pendulum swings – the greater the length the less swings the pendulum will make in a given time

Pendulums The pendulum is a simple machine for transferring gravitational potential energy to kinetic energy, and back again… T = 1 ÷ f T = time in seconds and f = frequency in hertz

Pendulums When the bob is at the highest point of its swing it has no kinetic energy, but its gravitational potential energy is at a maximum - as the bob swings downwards, gravitational potential energy is transferred to kinetic energy and the bob accelerates At the bottom of its swing, the bob’s kinetic energy is at a maximum and its gravitational potential energy is at a minimum As the bob swings upwards, its kinetic energy is transferred to gravitational potential energy again - at the top of its swing, it once again has no kinetic energy, but its gravitational potential energy is at a maximum The bob’s swing will become lower with each swing, because some energy is also transferred as heat to the surroundings

Big Ben The mass of the bob does not affect the swing of the pendulum Why is it then that Big Ben’s timing is kept in check by adding or removing a penny? The idiom of putting a penny on, with the meaning of slowing down, sprang from the method of fine-tuning the clock's pendulum Adding or subtracting coins has the effect of minutely altering the position of the bob's centre of mass, the effective length of the pendulum rod and hence the rate at which the pendulum swings Adding or removing a penny will change the clock's speed by 2/5 th of one second per day

Big Ben – Conceptual Explanation Big Ben with its standard pendulum swing If Big Ben is running slow then a penny can be taken from the bottom, changing the centre of mass, effectively shortening the length so the pendulum swings quicker If Big Ben is running fast then a penny can be added to the bottom, changing the centre of mass, effectively increasing the length so the pendulum swings slower pivot

Big Ben Big Ben pennies – their additional slightly changes the centre of mass, so slightly affecting the timings of the pendulum swing (1 penny changes the swing by 2/5 th of 1 second per day)!