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+2 votes
1 lesson
In 4-6 by Petar Mares Guru (5.9k)  

Sound is a longitudinal mechanical wave. Mechanical wave means it needs physical medium to travel (air, water, some particles of matter), longitudinal means that unlike water waves the oscilations move in the direction of the wave, whilst with water as mentioned the water surfaces oscilates up and down thus perpendiclar to the direction of the wave.
A slinky can demostrate this rather well.

Image taken from: https://www.researchgate.net/figure/Illustration-of-a-transverse-wave-and-a-longitudinal-wave_fig6_327447483

Check out the video for demonstration

The frequency of oscilations determines the high or low pitch of the tone. The sound thus travels through air all the way into our ears where it transfers the oscilations onto our eardrums that then oscilate back and forth just like the bass speakers oscilate back and forth when they produce sound. The sound is than transfered through our hearing bones to the cochlea, a snail like organ in field with fluid in which we have stereocilia, hearing hairs that swing in the rythm of vibration of sound. Different stereocilia pick of different frequencies and transfer them into the hearing part of the brain.

Check out the video for more interesting information:

Sound can be recorded mechanicaly (cylinders, vinly records, cd-s), or magnetically (8-tracks, cassets, tapes, hard disks etc.)


+2 votes
1 lesson
In 4-6 by Petar Mares Guru (5.9k)  

Video about electricity, a bit advanced.

Thanks to Crash Course

+2 votes
1 lesson
In 4-6 by Petar Mares Guru (5.9k)  

Informative video about high and low pressure, a bit focused around Korea

Thanks to EBS Docs

+2 votes
1 lesson
In 4-6 by Petar Mares Guru (5.9k)  

Water can be liquid in room temperatures. If we put it in freezer, water will freeze, become solid and turn to ice. If we boil water for our tea or coffee we will notice water vapor. If we boil water long enough we will turn all of our liquid water into water vapor.

This is a great examples of three states of matter: SOLID , LIQUID and GASEOUS.

Find out more at https://thebeakerlife.com/homework-helper-states-of-matter-a721b953c14c

Image from BEAKERLIFE, find ot more on their website

Water will freeze on 0 ºC, zero degree Celsius and below, and turn from liquid into solid. If we warm it back up it will melt it again to liquid water, and if we warm it even further to 100 ºC it will start boiling and eventually turn into gas.

So by increasing the temperature, we can turn water into gas and by decreasing it we can turn it into its solid form or ice.

But this goes not just for water, any substance can have solid, liquid or gaseous state. However some materials like metal are solid already at room temperature and require very high temperatures to be turned into liquid or gas, while some other substance like nitrogen (one of the gases that make air that we breed) require very low temperatures to be turned into liquid (−195.79 ºC) and even lower to be turned into solid.

The reason this happens lies in the structure of each state. In solid state, particles of given substance are connected by strong bonds, thus making it solid. Temperature will make the particles vibrate until they vibrate so hard they finally brake the bonds and the substance changes state from solid to liquid. In liquid state particles will still be connected by loose bonds and if we continue to heat up the given substance even more we will finally brake all the bonds and turn it to gas.

Check out this interesting video to learn more.

+2 votes
2 lessons
In 4-6 by Juhani Katajamäki Guru (6.1k)  

First let's see a very nice way how to practically prove that triangles always have 180° sum of angles.
Check out this video:

Cool right? You can try this yourself with any triangle you care to cut out.
Try and see if you can make one whose angles don't add up to 180.

Image source: Omnicalculator.com

This means that at all times we can calculate the third angle if we know the other two in any triangle.

So let's try this out!


Let's say we have a triangle just like one in the image above and let's say it's known angles are α=25°, β=75° (this doesn't necessarly have to be true for the image above, we use triangle images often more as a sketch than an actual drawing). The third angle, angle γ is unknown and we need to find it. Therefore we write:

α=25° β=75° γ=?

α + β + γ = 180°

γ = 180°- (α + β)

α + β = 25° + 75° = 100°

γ = 180°- 100°
γ = 80°

So we calculated the third angle by substracting the sum of first two from 180°.

+2 votes
2 lessons
In 4-6 by Makaela Anderson Guru (7.6k)  


Storytelling is an excellent way to practice all four learning skills: reading, writing, listening, and speaking.  Review the storytelling verbs, say, tell, speak, and talk, then grab 2 or more friends and play the Circle Storytelling game.

How to play Circle Storytelling:

  1. Everyone sits in a circle together.
  2. The first person to speak begins to tell a story by saying the first 3 sentences.
  3. Going counterclockwise (or anti-clockwise), the next person makes up the next three sentences of the story.
  4. Go around the circle and give each person a chance to create 3 sentences to add to the story.
  5. Keep going around the circle as many times as needed (at least 3 times) until the story finished.

The story can be of any genre, adventure, mystery, drama, comedy, etc.  With so many storytellers, it will surely be a fun and unique story!

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