Scenario Presentation 2

We had the rest of the scenario presentations. There were 3 groups left. The first group had this scenario: In a production line, 10000 small screws are to be sorted into packs of 50 each. Manual counting would be too tedious. Suggest ways in which the sorting may be done.

This problem seems quite tricky. However, if you think hard about it, the solution is actually pretty simple.


The group had two solutions. 1. Use an electromagnet. Adjust the resistance of the electromagnet such that it attracts 50 screws each time. However, Mr. Lim said that this solution was not very relevant as the electromagnet would be likely to attract either all the screws or none at all. Hence, this solution was not likely to work.


2. Use a weighing scale. Count the first 50 screws and weigh them. Subsequently, grab a handful of screws and weigh them. Compare the reading to the first reading of 50 screw and adjust the number of screws accordingly. This solution is both practical and feasible. It is based on how shopkeepers weigh biscuits or ham using the weighing scale and add more or take out some based on the weight of the products.


The next group had a relatively more common scenario, but explaining it was more difficult. This was their problem: A spring balance will give a different reading on the Moon than from that on Earth. A beam balance, however, will give the same reading. Explain why.


The group's answer is as follows: A spring balance measures weight, which is dependant on gravity. The Moon has less gravity than the Earth, hence the reading differs. However, a beam balance measures mass, which is constant no matter what. Short and sweet, but very clear.


The final group had a very interesting topic. How do submarines float and sink at will?


In my opinion, this group had the most detailed presentation. They explained how air is pumped into the ballast tanks to force water out so that the submarine would float. On top of that, they included a lot of other information such as diagrams, and information on the Kursk Russian submarine disaster. They talked about how a faulty Dummy torpedo had allowed flammable liquid to leak through and explode the front of the submarine, letting water in and causing the submarine to sink.

At the end of the presentation, they gave us question to think about: If a submarine sinks to the seabed, why is it no longer available to move off? The answer is that there is no water under the submarine to create a lift force, hence the submarine is stuck there until rescue workers drop a rope down to haul it back up. I enjoyed this group's presentation the most.

I enjoy thought-provoking lessons and topics like the ones Mr. Lim gave us. I hope we'll be able to have more of such lessons in the future.

Scenario Presentation Part 1

We had to present our work to the class. Li Shan's group went first. They were supposed to measure the approximate amount of water in Mac Ritchie Reservoir based on the map and the fact that the reservoir was 5 m deep.

They certainly thought through their scenario very well. The group gave two possible solutions. The first was to use the scale to calcuate the length and width of the reservoir, then multiply it by the depth for the final answer. The second was to draw the shape of a cylinder on the map. The cylider covered most of the reservoir. After that, they used a formula to calculate the volume of the cylinder and used the scale to convert it to live size. I found the presentation clear, concise, well-thought and interesting.

It was our turn next. I think we did okay. At least no one seemed confused when we explained our method.

We were supposed to finish off all the group presentations, but we were running late again.

Physics Scenario Slides

Scenario solving

Okay, this post is rather late but I didn't have much time to set up the blog earlier on. Anyway, Mr. Lim gave us these scenarios to solve. We were supposed to come up with solutions to our assigned scenario in groups. I was in the same group as Jasley and Abigail. Our scenario was as follows:

You are given a length of copper wire with a small diameter. The only measuring instrument available to you is the meter ruler. Explain how you would measure the diameter of the wire with an acceptable degree of accuracy.

At first, we were stumped as it seemed impossible. Then, Mr. Lim told us we could have a pencil to use as part of the materials. After that, everything just snapped into place. We came up with a simple but effective solution:

To find out the diameter of the copper wire, first we have to twirl the wire round the pencil. Then, measure the length of the pencil. Then, find out how many twirls it takes to make the circumference of the pencil and divide it for the diameter of the copper wire.

Pretty neat, isn't it?