## Measuring Difference in Drop Time Using PhyPhox

In a recent class on Kinematics, I prepared a string of 4 pendulum balls, each separated about 20 cm apart and dropped them from a height. Before that, I got students to predict whether the intervals in time between drops will be constant, increasing or decreasing.

Most students are able to predict rightly that the intervals will be decreasing and explain their reasoning.

What challenged me was this: previously, we had to listen to the intervals of sound to verify the answer. I had tried using laptop software such as Audacity to record the sound before. However, I wanted students to be involved in this verification process. PhyPhox enabled that.

With each student being able to download the mobile app into their phones, all I needed to do was to ensure everyone uses the correct setting: the Audio Scope setting and to change their range to the maximum duration (500 ms). They then had to be familiar with the play and pause button so they can stop the measurement in time to see the waveform.

I then did a countdown before dropping the balls. This is an example of the graph obtained.

Through this graph, you can see that:

1. the time interval between drops decreases as the balls dropping over a larger height had gained more velocity by the time they reach the table.
2. the amplitude of sound increases as the balls drop with increasing velocity, therefore hitting the table with larger force.

## Template for Creating GeoGebra Animations

In an introductory sharing for the use of GeoGebra to my colleagues, I have prepared a simple template for them to try their hands at animations of points and other elements.

You can try the same too. Create a moving point by typing into the Input field (5,5*sin(time)) so that you get a point at x = 5 that oscillates between 5 and -5 in the vertical direction.

## Relationship between displacement-time and velocity-time graphs

Through this GeoGebra app, students can observe how the gradient of the displacement-time graph gives the instantaneous velocity and how the area under the velocity-time graph gives the change in displacement.

In the GeoGebra app below, you will see a displacement-time graph on the left and its corresponding velocity-time graph on the right. These graphs will be referring to the same motion occuring in a straight line. Instructions

1. Click “Play” and observe the values of displacement and velocity change in each graph over time.
2. Note the relationship between the gradient in the displacement-time graph and the value of velocity.
3. Note the relationship between the area under the velocity-time graph and the value of displacement.

## Instantaneous vs Average Velocity

This GeoGebra app allows students to observe the difference between instantaneous and average velocity from a graphical perspective.

## Work Done Simulation

This GeoGebra app allows users to change the magnitude and direction of the force acting on an object, as well as the initial velocity.

The change in kinetic energy is calculated along with the work done in the direction of the force.

This demonstrates a very important concept in Physics known as the Work-Energy Theorem, where the net work done on a particle equals to its change in kinetic energy.

## Review of Sci-sational Christmas at Science Centre Singapore

In a nutshell, Sci-sational Christmas offers value-for-money interactive family festive fun.

Open from 1 to 25 Dec 2019 at the Annexe of Science Centre Singapore, visitors will enter 3 main activity zones:

## Zone 1: Hot vs Cold Experiments

Watch as two “elves” try to outdo each other by performing scientific demonstrations based on opposing ends of the temperature range – under very carefully controlled conditions of course.

The number of asterisks show the loudness of the explosion. The heat experiments in the “Fuel Efficiency Department” are:

1. Lighting of a hydrogen balloon (**),
2. Lycopodium powder combustion (*), and
3. Ethanol-powered propulsion (***)

Over at the “Alternative Energy Department”, the elf tried to impress us with:

1. Boiling of liquid nitrogen, increasing gas pressure to burst a balloon (***),
2. Liquid nitrogen propelled plastic bottle rocket (*), and
3. Liquid nitrogen cloud formation with hot water

To me as a science teacher, these experiments would have made the tickets worth the money already. After all, demonstrations like these are usually the highlight of science museums all over the world. But there are more…

## Zone 2: Scented Candle Making

After exiting the first workshop, visitors are brought to the candle making workshop. We were each given a rubber mould, some melted soy wax, colouring and a few drops of liquid scents to make our own Christmas tree candles.

Do take care not to add too much colouring or the tree may not freeze evenly and hence, break easily. On hindsight, I should have used mainly non-coloured wax with a little green colouring for the base of the candle (to pour in last) to get a snow-covered Christmas tree.

## Zone 3: Escape Room

The escape room offers plenty of fun for the kids in the group. There are clues planted all over Santa’s office and the session is facilitated by an “elf”. The aim is to unlock a number lock under the fireplace in the office for the kids to crawl out from.

There is a secret door for the grown-ups, though, so we need not worry about our outfit or painful knees.

The only downside is that visitors are placed in groups of 15-20, most of whom are strangers – unless you register as a big group of friends. However, most kids would often get quite involved and interactive despite not knowing one another.

I highly recommend this activity for families with kids aged 5-12. At a price of \$15 that includes general admission to the Science Centre, it is far more worthwhile than a conventional escape room experience in Singapore and is something my own kids find meaningful and exciting.

I have a feeling that the Science Centre might organise more escape-room styled activities in future as they are quite the craze nowadays.

Visitors might want to note that the 3 zones would last a total of about 50 min. The entry timings are: 11AM, 12NOON, 1:30PM, 2PM, 2:30PM, 3PM, 3:30PM, 4PM and 4.30PM. You will need to indicate your preferred timing when purchasing the ticket and show up on time at the entrance, which is near the fire tornado exhibit.

## Uniform vertical circular motion

The following GeoGebra app simulates the force vectors on an object in uniform vertical circular motion.

A real world example of this would be the forces acting on a cabin in a ferris wheel.

<iframe scrolling="no" title="Vertical Uniform Circular Motion " src="https://www.geogebra.org/material/iframe/id/t5jstqsm/width/640/height/480/border/888888/sfsb/true/smb/false/stb/false/stbh/false/ai/false/asb/false/sri/true/rc/false/ld/false/sdz/false/ctl/false" width="640px" height="480px" style="border:0px;"> </iframe>

## Vertical Non-Uniform Circular Motion

This is a simulation that shows the vectors of forces acting on an object rolling in a vertical loop, assuming negligible friction.

To complete the loop, the initial velocity must be sufficiently high so that contact between the object and the track is maintained. When the contact force between the object and its looping track no longer exists, the object will drop from the loop.

The following code is for embedding in SLS.

<iframe scrolling="no" title="Vertical non-uniform circular motion" src="https://www.geogebra.org/material/iframe/id/ny3jhhsp/width/640/height/480/border/888888/sfsb/true/smb/false/stb/false/stbh/false/ai/false/asb/false/sri/true/rc/false/ld/false/sdz/false/ctl/false" width="640px" height="480px" style="border:0px;"> </iframe>

## Aircraft Turning in a Circle: a 3-D Visualisation with GeoGebra

This GeoGebra app is a 3-D visualisation tool of the force vectors acting on an aircraft turning with uniform circular motion in a horizontal plane.

I prepared this in advance as I will be lecturing on this JC1 topic next year.

## Does Hydrostatic Pressure Depend on Container Shape?

The following GeoGebra app simulates a pressure sensor that measures hydrostatic pressure, calibrated to eliminate the value of atmospheric pressure.

The purpose of this simulation is to address certain misconceptions by students such as the assumption that the shape of a container affects the pressure such that the pressure differs in different containers when measured at the same depth.

Drag the dot around to compare the pressure values at the same height between both containers.

The following codes can be used to embed this into SLS.

<iframe scrolling="no" title="Hydrostatic Pressure" src="https://www.geogebra.org/material/iframe/id/wbjduxt7/width/640/height/480/border/888888/sfsb/true/smb/false/stb/false/stbh/false/ai/false/asb/false/sri/true/rc/false/ld/false/sdz/false/ctl/false" width="640px" height="480px" style="border:0px;"> </iframe>