Practicals 6 to 10

Measuring Lengths- The instruments!
The Science Lesson
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The Vernier Caliper

The Micrometer Screw Gauge

The Metre Rule

You guessed it, this Science lesson was about the different tools used to measure varying lengths!
  Upon seeing the instruments, I was fascinated. I had not known about most of this equipment before, and was itching for the opportunity to use one.
  Firstly, we started off with the basics. A metre rule (I'm sure most of you are familiar with this object) was to be examined and after doing so, we discovered that its smallest reading (i.e. one division on the ruler) was 0.1cm. We then proceeded to measure the heights of our seats from 4 different positions. Unsurprisingly, the results showed little variation and the average height was easy to find.
  Following this, it was time to use the vernier caliper! Its unique appearance intrigued me and after inspecting it, I realised that it was effectively 10 times more accurate than a metre rule- that is, it could measure lengths up to 0.01cm accuracy. Here, we were introduced to a new term: Zero error. Zero error occurs when the zero marking on the vernier scale is either to the left (negative) or right (positive) of the main scale. Zero error can be rectified by either adding (for negative zero error) or subtracting (for positive zero error) the zero error value to the reading. Afterwards, we used the vernier calipers to measure the internal and external diameters of a beaker. This was achieved by utilising the two jaws of the vernier caliper (the sliding and the fixed jaws).
(Use your imagination to replace coin with beaker)
  Last but not least, the micrometer screw gauge was given to us to examine. I discovered that it was even more accurate than a vernier caliper, capable of measuring lengths up to 0.001cm accuracy! Be warned though, zero error has the potential to occur for this instrument as well! We used the micrometer screw gauge to measure the diameters of a wire and a ball, and I was impressed by the accuracy of the results.
Micrometer screw gauge in action!
  I found this lesson very fulfilling in two aspects: I had satisfied my natural curiosity and learnt how to use two new instruments with the ability to measure lengths with much greater accuracy than a standard ruler. I anticipate the next lesson!


  This Science lesson revolved around an apparatus known as the pendulum. Having seen this in the Tintin series, I was curious to know what purpose it served. Let's start off with a diagram of a typical pendulum:
For this case, l =100cm
  After giving the pendulum bob a slight displacement, we set the pendulum into oscillation (1 oscillation -> from A to C then back to A or vice versa). We timed 10 oscillations using a stopwatch, recording the time as t1. We repeated the timing for another 10 oscillations and recorded the time as t2We calculated the average timing and named it <t>. To find the period, we simply divided <t> by 10, recording the result as T
  We then shortened the string, thus decreasing the value of l. We repeated the above steps but using varying values of ranging from 50.0cm to 90.0cm. Our task was to tabulate the values of l, t1, t2, <t> and T. In addition, we had to plot a graph of against l. Judging from the graph, I concluded that the shorter the length of the pendulum (l) , the shorter the period (T). 
  As with all scientific equipment, precautions must be taken to reduce the chances of an error occurring. Here are some tips to increase the accuracy and reliability of one's readings while using a pendulum:

  1. The angle of the swing must be less than 10 degrees.
  2. The pendulum must be swung in a plane.
  3. To prevent human reaction time error, start timing the pendulum only after a few oscillations.
This concludes the summary of what we learnt for this practical. Look for more updates soon!


Density of regular objects

  Density. I had heard of the term before, but at best my comprehension of it was shallow. Thus, I anticipated this lesson as it would let me gain a deeper insight into the definition of this term.
  First off, we were assigned a simple task: Weigh an empty plastic bottle and 5 marbles together. We then weighed only the plastic bottle, after which we subtracted the plastic bottle's mass from the total mass to get the mass of the 5 marbles.
  Following that, we divided the mass of the 5 marbles to find the mass of a single marble. Utilising a micrometer screw gauge, the diameter of a marble was measured. The volume of each marble was calculated using this formula:
(where π is 3.14)

  Finally, we determined the density (which means mass per unit volume) of a marble 
via this formula:
Note: This formula can be altered to find the mass and the volume as well 
(e.g. volume= mass divided by density)

We did a few exercises associated with density to ensure that we understood the concept 

This lesson was an enriching experience and I hope the following lessons will be the same. 

Keep your eyes peeled for updates soon! :)


Density of irregular objects

In the previous practical, the techniques to calculating the density of a regular object. For this lesson, we would be learning how to do the same for an irregular object.
  The first step in the procedure was a relatively simple one. In fact, most of us had done the same in our respective primary schools during experiments. We weighed a glass stopper and recorded the mass as M, then filled a measuring cylinder to approximately one-third of its depth with water, taking note of the volume, which was named V1.

The volume of liquid without anything in it

 After tying the glass stopper using a piece of string, we gently lowered it into the water until it was fully submerged. We then measured the current volume and noted it as V2.
Volume of liquid with glass stopper inside
 Finally, we subtracted V1 from V2 to obtain the volume of the glass stopper. We then proceeded to repeat the above mentioned steps twice to increase the consistency and reliability of the results.
  We utilised a familiar formula to calculate the density of the glass stopper. To refresh your memory, here's a large illustration:
  Here are some things to watch out for when taking readings with a measuring cylinder:

  • Avoid parallax error when taking readings
  • Reading must be taken on a flat surface
  • For accuracy of results, take readings from bottom of meniscus (the curve in the liquid)
I will be updating the ePortfolio with the next Practicals soon, don't forget to check for new posts! :)

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Brownian Motion
  Hi everyone! After more than a week, I'm finally back- this time with a practical on Brownian Motion!
  So, what is it? Well, fundamentally, Brownian Motion is the constant and erratic movement of particles suspended in a liquid or gas. Yes, it's essentially random, and could possibly look like this:
(Drawn hastily using paint)
That's just one example. Varying diagrams show differing movement of particles, but it does not really matter because the movement is not based on a pattern.
  Is that it? Are we simply going to accept that without verifying it? Of course not! We proceeded to carry out an experiment to confirm this theory.
  Firstly, we filled a smoke cell with smoke from smouldering paper and covered it with a glass slip. Then, we illuminated the particles of smoke with a bright source of light. Last but not least, we examined this with a low powered microscope placed at a 90 degree angle to the direction of the light and recorded our observations.
  We noticed that bright spots of light were in continuous random motion against a dark background. These bright spots were identified as smoke particles which had reflected the light from the source. Following which, we selected a specific spot and sketched its progress, which was quite entertaining.
  The reason behind the smoke particle moving in the manner mentioned above was because of the fact that air particles bombarded the smoke particle unevenly on all sides. To make comprehension easier, visualise a large ball being hit by numerous smaller balls which are constantly moving which causes the larger ball to "bounce" around randomly. Here's an apt animation:
Small balls: WHACK THE BIG ONE!
Big ball: Ouch ouch ouch!
  From this practical, we also learnt that the higher the temperature, the more kinetic energy the particles have and thus the faster their movement. Also, larger particles, possessing more inertia (i.e. the resistance of an object to a change in its state of movement or rest) will move slower than smaller particles, thus allowing one to differentiate between the two.
  This practical was a very fascinating one and I enjoyed the hands-on activity. Look out for the next one :)

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