Science week 3 - Investigating the viscosity of liquids. 

The flow of a liquid is described as its viscosity. Some liquids are very runny and so are not very viscous, however others are very gloopy and thick. These liquids are said to be very viscous.

In the lesson we are going to investigate the order some liquids according to their viscosity.

When we plan an investigation, the first thing to think about is the variable which we will change. In this experiment we are comparing the viscosity of a number of liquids, so the liquid itself is what we are changing. We call this the independent variable. In the experiment below they test water, lamp oil, milk, rubbing alcohol, vegetable oil, maple syrup, washing up liquid, olive oil, corn syrup, and honey. Which one do you think is most viscous? Make a prediction now and write it down.

The next consideration when we plan our experiment is what do we need to measure to work out the answer to our question? We call this the dependent variable. Today we are going to measure the time a liquid takes to flow down a tray in seconds.

Finally the next stage when planning our investigation is to make sure all the other parts of the experiment stay the same for each liquid to make it fair. These are the control variables. In today's investigation it is important to use the same volume of liquid each time, to have the slope of the tray the same and also the same start and finish points.

Below is a video of the experiment. If you would like to do your own versions at home after you have watched this video you can but please check with an adult at home first to get permission.

Now that you have all the measurements for the experiment please write up the experiment under the following headings.

What are we trying to find out?

What is our independent variable?

What is our dependent variable?

What are our control variables?

How to do the experiment:

Results: The times each liquid took to go down the slope. Write these in a table please.

Conclusion (What we found out): In sentences explain which liquids were the most and least viscous and use their data to explain how you know this.

Please send your write up to me as a task.

Here is an example if you are stuck.

Homework: When we do an experiment, we sometimes take repeated measurements to check that they are correct. We then work out the average by adding all the measurements and dividing the answer by the number of measurements we added.           e.g. Find the average of 6.7, 8.7 and 9.4.                                                                                                     6.7 + 8.7 + 9.4 = 24.8                                                                                                                                             24.8 divide by 3 = 8.27 This is the average.                                                                                                 Your homework is to calculate the average of the numbers on each line and write the answer in the final column. If you notice a number which doesn't seem to fit the others in the row, circle it. We call this an anomaly. There is only 1 on this worksheet.

Please bring your homework sheet to next week's lesson.