Feynman on kinetic model

This week I am doing work and energy with my Y3 students. We started with the concept of work and went on to the activity bouncing ball activity shown below.

Bouncing Ball Activity

Explain:

• Describe the conversion of energies during the motion from point of release to just before hitting the surface 
• Explain why the returned height after each bounce is less

Students' explanation on why the ball has a lower height after each bounce

It is a rather common for learners to associate any lost in mechanical energy as "being converted to heat". It is probably because of the fact that they have experienced the warmness due to phenomena such as rubbing their palms, hitting a nail, etc.

Qualitative understanding of the energy exchange during the bounce

What really happens requires the understanding of the following concepts:

• Temperature is a macroscopic observable/measurable of the average kinetic energy of random molecular motion
• The contact between the ball and the floor increases the random molecular motion at the expense of the ordered mechanical energy. This causes the temperature of the ball and floor to rise or we say that the internal energy of the system increases.
• Assuming that the ball and floor is at thermal equilibrium to the surrounding, the increase in their temperatures result in a net transfer of heat to the surrounding, i.e. the warmness we feel if we are to touch them (the temperature difference is likely to be less than what we can perceive in reality).

In addition, we can also apply the same thinking to conclude that the movement of the ball through the air also increases the internal energy of both the ball and the surrounding air.

Feynman's explanation below (from about 1min45sec to 3min15sec) really sums it for learners and most importantly encourages them to enjoy thinking about science.

Gowth Mindset

Fostering a growth mindset in learners (children, adults) may be one of the key to improve learner's motivation to learn, ownership of learning, perseverance, etc.  As teachers, we may not have been tackling the root cause of these learning characteristics.

Learners will benefit greatly from a changed mindset about learning.

The benefits of a Growth Mindset - Carol Dweck

 The Power of Belief - Mindset and Success: Eduardo Briceno at TEDxManhattanBeach

Physics of Haze

I couldn't help it but to apply what I know in Physics to explain the white/gray haze as a result of the smoke particles from the Sumatran fires.

To begin, let's try to understand how we see the colours of the buildings and the trees. We "see" the colour of the light that is scattered off the surface of the building, leaves, etc, as shown.

Scattering of light from surface (e.g. green wavelength em waves from the leaves) causes us to "see" the objects' colour

Light is also scattered by the air molecules (~ nanometer in diameter) along the path from the sun to the object by a process known as Rayleigh Scattering (refer to my previous post) towards the observer. However intensity from this scattering is low compare to the intensity of light reaching the objects and scattering to the observer. Generally our eyes cannot sense this low intensity in the presence of the light from the objects.

Effect of Rayleigh Scattering is small and hence don't produce the white haze 

With the dust particles, diameter in the region of microns (0.000001 m), suspended in the air, Mie scattering dominates. The scattering intensity by this process is larger than Rayleigh Scattering. The larger intensity of white light scattered from these particles (consisting of all visible wavelengths) is now more obvious to us.

Mie Scattering off the dust particles produces the white haze seen the above photo

The additional scattering also explain why the sky and the sun appears red around 6 pm, something we usually observe around 7pm when the sun is close to the horizon.

Red sky and sun around 6pm

For more information on the different type of scattering, you may want to refer to this.

Using Tracker to study solar spectrum (with absorption lines) for the topic of Quantum Physics

Line Spectral with Tracker
Created this instructional video on "using Tracker for spectroscopy". Youtube link is here.


Lessons that took place before this activity Students could have

• observed the emission spectrum of elements such as sodium, neon, mercury, kryption, etc. although they do not have hands-on experience of setting up and adjusting the apparatus.
• gone through the theory and tutorial on the section of spectral lines.

Resources
Below is the worksheet that students will attempt.

Analysing solar spectrum from Lee Tat Leong

Pictures of the solar spectrum and the emission spectrum of different elements (derived from the picture here and here).

• Hydrogen (H)
• Helium (He)
• Sodium (Na)
• Magnesium (Mg)
• Solar spectrum

Disadvantages of hands-on approach

• Experiments on spectral lines are time consuming due to the difficulty in setting up and calibrating the spectrometer.
• The other big challenge is the availability of a suitably dark room to observe the emission spectrum of discharge tubes.
• The availability of sufficient apparatus for experiments.

Advantages of using Tracker

• Cheap.
• Easy to deploy.
• Easy to operate to obtain quality results for comparison and analysis because students  can now focus on the actual physics rather than on the setting up of the experiment.

What is a Field?

This is the Physicists' way of looking at the field concept. Kind of difficult for layman like us to understand. Enjoy :-)

From Scientific American