How long can a bubble last? You have recently been placed in a research team to help provide information for your company about their soap product. A customer has complained – she says that the liquid produces bubbles that burst instantaneously.
Your task Your team’s task is to carry out experimental procedures and discover the conditions needed to produce long lasting bubbles.
Safety This is a fairly low risk lab You will be using a glass dropper which will cut you if you break it Don’t let the soap solution get into your mouth Remember: Tell the teacher about any spills or breakage
Equipment checklist Find the equipment checklist in your box Make sure you have all of the equipment You will have to check everything on the list back in at the end of class so make sure it’s not missing before you start
Set up your notebook Write a title – center it, underline it, make it look like a title. Call it “Investigating factors effecting bubble lifetime.”
Objectives You will: Investigate the effect of soap concentration on the lifetime of bubbles Design an experiment to test the effect of bubble size on lifetime Plot graphs of your data to help you interpret it Report your findings to the company
Practice blowing bubbles For these experiments, you will need to be able to blow bubbles that are consistent - the same every time. Before starting, follow the following instructions and get some practice.
First make your “Blower” Make sure your whiteboard is clean of dust. Insert one end of the straw into glass dropper (that doesn’t have a rubber bulb on it) Then tape around the join.
Set up the soap solution Using the other dropper, put 1ml (20 drops) of soap solution in the center of the circle.
Blow the bubble Insert the sharp end of your “Blower” into the pool of soap solution and blow gently until the bubble fills the circle. Then Stop. If more than one bubble forms, wipe the whiteboard and start again
Take some data Write a heading in your notebook and copy this table.
Taking data Now blow a bubble Stop as soon as they reach the size of the circle and start your stopwatch Stop the watch when they pop Write the time in table Repeat four times
Analysis Why do we need to do it more than once? Write the answer in your notebook as a full sentence: “We timed four bubbles because…”
Experiment One:The effect of concentration A Concentrated soap solution has more soap in the same amount of water than a Dilute solution. Concentrated Dilute
Your task You are going to investigate what happens to the lifetime of a bubble as the concentration of the soap solution increases and becomes more concentrated.
Hypothesis Scientists start an investigation with a hypothesis – a prediction. The hypothesis does not have to be correct and often are found to be wrong. Not a problem – it all adds to scientific knowledge. What do you expect to happen to the lifetime of the bubbles as concentration increases? Do you think they will last longer with a concentrated, strong soap solution or a weaker, dilute solution?
Write a hypothesis Write a title “Hypothesis” in your lab book and write what you think – include enough words so that it’s clear to anyone who picks up your book. Start it like this: “If the concentration of the soap solution increases, then bubble lifetime will ……”
Procedure Your Sample will be 4 bubbles. 3 different concentrations of soap solution are provided: 4ml soap per 100ml 6ml soap per 100ml 10ml soap per 100ml Which is most concentrated? Check your answer with a teacher. For each concentration of soap solution, you will blow an 8cm bubble and measure its lifetime.
Collect data Draw this table in your lab book and collect your data:
Analysis What is your Independent Variable ? This will go on your X axis. (HINT: Which variable are YOU changing?) What is your Dependent Variable? (HINT: Which are you measuring?) Write a note in your notebook: Independent variable: _________________ Dependent variable: ___________________
Graphing You need to draw a graph of your data. What kind will you draw? Remember that you use: a bar chart you are measuring a series of unconnected data; a line graph if you are analyzing data that changes continually; or a pie chart if you are comparing fractions or percentages of a whole.
Graphing (cont.) Draw your graph on graph paper and stick it into your notebook . Remember to label the graph and label each axis.
Analysis (cont.) What happened to the lifetime of the bubble as you increased the concentration? Was your prediction correct? Whether you predicted the correct result or not does not matter – now you know the answer. Write your answers in your notebook
Experiment 2: The effect of Size Will larger bubbles last longer than small ones? You must find out. Investigate the lifetimes of bubbles with diameters between 3 and 8cm. Diameter
Hypothesis What do you think will happen to the lifetime of bubbles as you increase the diameter? Add a new heading to your notebook for this experiment and write a hypothesis. HINT: look at your last hypothesis for ideas…
Variables What will your Independent Variable be? What will your Dependent Variable be? What will you keep constant? Write a list in your notebook: Independent variable = ___________________ Dependent variable = ____________________ Constants = _____________________________
Procedure Now you know: What you are changing What you are measuring What stays the same Write a Procedureto check your hypothesis Use numbered steps so that anyone would understand it and know what to do
Data Before you start, draw a data table in your notebooks. Ask a teacher to check it and your procedure before you go any further.
Analysis Plot your data on a graph – use graph paper. Remember: The independent variable goes on the x axis The dependent variable goes on the y axis What kind of graph are you going to use? According to your graph, what happens to bubble lifetime as bubbles get bigger? Was your prediction correct?
Report Now write a short Memo to your boss explaining what you have discovered. Do the bubbles burst instantaneously like the customer complained? What should your boss tell the customer to do if they want their bubbles to last longer? Write the report in the style of a “Memo”. That is how people write to eachother inside a company. The next slide shows you how to format the memo.
Memo From: Your name To: Your boss’s name Date: Today’s date Blah, blah, blah…
Cleanup Congratulations – you have finished the assignment Now wipe off your whiteboard Throw away the straw that you used in your “Blower” Put everything back into your lab box and check the equipment list as you do so. Call a teacher to check that everything is in the box before you put it away.