Introduction to light and sound

Light and sound both travel in waves. In this unit we will jump back and forth when investigating light and sound but the following section compares the speed of light and sound.

Play the looking game, 'I spy'.

Play the hearing game, 'Heads down, thumbs up'.

The speed of light and the speed of sound

The speed of light is the fastest thing that we know of in the universe. According to Einstein's theory of special relativity, no matter or information can travel faster than this, as doing so would require infinite energy. The speed of sound is also very fast but nowhere near as fast as light. You might have seen examples of this during a thunderstorm as we see the lighting before we hear the thunder. The speed of sound is around 343 metres per second (m/s) but the speed of light is around 299,792,458 m/s. How can we make sense of such big numbers? Here is a comparison which might help:

Q: If you measure how far light travels in a single second, how long would it take sound to travel the same distance?

A: It would take around 10 days!

Does the amount of water in a bottle make the sound higher or lower?

The following video (2:14) investigates this question but to sure to let your students try this out for themselves before you show them the video.

A good explanation of this phenomena can be found at https://www.scienceworld.ca/resource/musical-bottles/.

Angles

The following video (6:25) is an introduction to angles.

Reflection

Light travels in straight lines which can create some interesting results when reflective surfaces are involved.

Building a periscope

In this video (4:25) you will see how a periscope can be made to see around corners.

Colour wheels

A colour wheel can be attached to a pencil and spun to create the visual effect of merging all of the colours into white.

https://www.pngegg.com/en/png-oykqp

Refraction

Refraction is the bending of light (or other waves like sound and water) as it passes obliquely from one transparent medium to another, such as from air into water or glass. This phenomenon is caused by a change in the wave's speed, which alters its direction. It is responsible for effects like magnified images, rainbows, and making submerged objects appear shifted.

(Image source K.Venkataramana CC BY-SA 4.0 Wikimedia Commons)

The Doppler effect

The Doppler effect describes how moving objects which emit waves affect the perceived frequency of those waves to observers. This phenomenon is named after the physicist Christian Doppler, who described it in 1842. The following video (3:02) explains this phenomenon in the common form of sound but also looks at light and stars as another example of the Doppler effect.

Sonic booms

This short video (0:45) explains the physics behind sonic booms.

Cracking a whip is another way to create a sonic boom. The following video (0:06) shows Brendan Jacobs, Chief investigator of The SILO Project, cracking a whip for the first time in his life before purchasing one from a vendor at the Tamworth Country Music Festival.

Making and/or using whips is an engaging activity for children but care should be taken that the students are well clear of cracking whips to ensure their safety. Click on the risk assessment icon for additional information.

The following video (0:51) shows this supersonic phenomenon in slow motion.

Moderated self-assessment

Discussions with students around the key components of conceptual topics and how they fit together can generate insights into student achievement.

We welcome your feedback and suggestions

The chief investigator for The SILO Project is Associate Professor Brendan Jacobs, Head of Department STEM Education, University of New England. The SILO Project thrives on incremental improvement so constructive feedback is greatly appreciated. Please contact Brendan via email at bjacobs7@une.edu.au to share your thoughts and recommendations.

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