Liquid Friction.

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Nick Earnshaw

Bedford School

Candidate 3440

AS Coursework – Making Sense of Data

“Liquid Friction”

Apparatus

Not in diagram:

  • Stopwatch
  • Top pan balance (accurate to nearest 0.1g)
  • Micrometer screw gauge
  • Several different size ball bearings.
  • Small magnet
  • Long ruler

Method

The apparatus was setup as on the previous page, a ruler was used to mark the depths of 0.2m and 0.7m. The glycerol was left to settle.

The mass of each steel ball bearing was measured using a top pan balance and the diameter was measured using a micrometer screw gauge. The results from this were recorded and each measuring device was reset to zero each time.

Each steel ball bearing was coated in glycerol and then released from just below the surface of the glycerol, using tweezers.

The time taken for each steel ball bearing to drop from a depth of 0.2m and 0.7m was timed using a stopwatch and then recorded. This step was repeated a further two times for each steel ball bearing.

The steel ball bearings were retrieved after each attempt, using a small magnet.

Results

I have formatted a table with the data attained from the experiment described above, each row of data relates to a different steel ball bearing.

The density of glycerol used was 1262 kg/m3.

* This mass could not be accurately recorded using the top balance.

Strategy and Approach

The above text is descriptive, it does not analyse the physics involved. My role within the investigation is to analyse results given to me. To effectively approach this target, I need to do some planning.

When the experiment was shown to me I took some notes, these are on a separate A4 lined sheet.

The initial ideas that I had whilst and shortly after the experiment was shown were:

  • Calculate the unknown mass
  • Identify and quantify the forces acting on the ball bearing
  • Look at the friction of liquid
  • Identify problems and try to realise solutions

These ideas allowed me to research things in more detail. Viscosity seams an ideal area to look into, and with the experimental data I have it seems possible to work out a value for its coefficient.

Whilst watching the experiment I noticed quite a few problems, I took notes which will help me later on in my analysis and more so in my evaluation of the investigation.

Method Notes

Where as the method previously described was completely descriptive of what happened. I am going to look into it with slightly more detail.

The tweezers were used to ensure that no finger grease got onto each ball, this is to create a fair test situation where each ball is treated in the same way.

Similarly, each ball is coated in glycerol. I presume this is to stop air bubbles forming; this would have a significant effect on the experiment.

Each ball was dropped from roughly the same place, but this was not measured.

The data collected was:

Time taken to move 0.7m – can be used to calculate speed

Diameter – used to show relationship between other things later in analysis

Mass – helpful to calculate forces

Other Notes

I converted the following, for later use in the analysis:

mass -> kg

radius -> m

velocity -> ms

All data is attached at the end of this investigation, in a separate data sheet – extracts of which are used in the investigation text.

In tables b represents ball bearing. Calculation values are shown up to 4dp or 2dp when expressed in standard form.

Calculating the unknown mass

This seemed to be the first logical step of my investigation, knowing the unknown mass may or may not be useful in other analysis. My approach is outlined below.

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mass = density x volume

volume of a sphere =

We have the diameter of the low mass ball.

radius =

We now have the volume of the low mass ball, to calculate its mass we need to find an average density of the steel used.

density =

The density for each ball is calculated excluding the unknown mass and the average is calculated. We can now use the first equation to give an estimate of the unknown mass.

From my calculations, the unknown mass is 0.0161kg

This ...

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