Exploring Sound Waves: Vibrations and Propagation

Sound Waves

• Vibrations create sounds.
• To vibrate means to move backwards and forwards very quickly.
• When drums vibrate, they produce sound.
• Hitting a drum with more force causes it to vibrate more, resulting in a louder sound.
• Vocal cords vibrate to produce sound when speaking.
• Loudspeakers create sounds from devices like TVs and radios. Small objects placed in a loudspeaker's paper cone will bounce due to the cone's vibration.
• Sounds vary in loudness and pitch.
• Thunder has a low pitch, while a baby's cry has a high pitch.

Sound Waves Explained

• Sound travels via vibrations to our ears in the form of sound waves
• When an object vibrates, it moves backwards and forwards.
• Each time an object moves forward, the air in front of it is pushed, causing air particles to vibrate back and forth.
• When air particles vibrate, they cause other particles in front of them to vibrate, creating a sound wave.
• Sound waves travel at approximately 343 meters per second in the air.
• A vibrating cone in a loudspeaker demonstrates how sound waves are produced.

Effects of Sound Waves

• Very loud sounds can damage the ears due to the intensity of air particle vibrations.
• A certain pitch can cause damaging vibrations, even at low volumes.
• Sound waves transfer energy.
• Vibrating particles in the air transfer vibration to other objects, causing them to vibrate.
• The glass can break from the vibration of a high-pitched sound.
• Very quiet sounds are too small for the ears to detect.

Sound Waves on the Move

• Sound waves travel by making particles vibrate, sound travels through gases, liquids, or solids.

Mediums and Sound

• Dolphins and whales use sound to communicate.
• The substance that a sound wave moves through is called the medium.
• Solids, liquids, and gases can all serve as a medium for sound.

Sound in a Vacuum

• To hear sound, there must be vibrations and a medium containing particles for sound waves to travel through.
• Vacuum is a space with no particles, so sound cannot travel in a vacuum as it has nothing to vibrate.
• If sound waves could travel through space, we would hear the Sun, which scientists think would sound like a high-pitched hum.

Reflections

• Sound waves, like all waves, can be reflected from surfaces.
• Sound waves bounce off a wall, similar to a ball.
• Smooth, flat, and large surfaces give good reflections of sound. Glass, tiles, flat metal, and smooth concrete are examples of surfaces that gives good reflections of sound.
• An effect on a sound means the sound is changed. When sound waves clap in an empty room, it is a strange effect on the sound.
• The clap sound seems to be longer, then fade away. Clapping creates a a sound wave that moves away in all directions and when the sound hits a wall, it is reflected back

Echos

• The reflection of a sound wave is called an echo.
• Bats use echoes to locate food; they emit a sound that reflects off insects, allowing the bat to determine the insect's location and direction by judging the time it takes for the echo to return.
• Boats use the same technique to measure water depth by sending a sound wave to the sea bed. The time taken for the echo from the seabed to return is used to calculate the water depth.
• Echoes can be used to create images from inside the body, such as in ultrasound imaging during pregnancy.
• Be aware that the distance travelled by sound is double the object making the sound of the reflecting surface

Unwanted Echos

• Unwanted echoes can alter sound, affecting things like music recordings, and therefore should be avoided.
• Large flat walls produce many echoes.
• Theatres are designed to stop echos as an audience needs a clear voice from the speakers.

Earth's Structure

• The Earth is about 4,500 million years old.
• The Earth's structure includes a crust of solid rock, a mantle of molten rock, and a core containing molten and solid metal.
• The rocks in the crust contain metals and non-metals.
• The most common elements in the Earth's crust include oxygen, silicon, aluminium, and iron.
• Alfred Wegener suggested that all land was one continent millions of years ago, drifting apart over millions of years, called continental drift.
• Geological change most frequently happens at plate boundaries because tectonic plates are always moving, this area is know as the Pacific Ring of Fire.
• Earth's crust is made up of tectonic plates, either oceanic or continental, that move slowly on the liquid rock, magma, resulting in continental drift.
• Oceanic plates are under oceans while continental plates form continents.
• The plates only move about 4 cm each year, about the same speed your finger nails grow.

Earth Changes

• Plate boundaries are where tectonic plates meet.
• Geological change happens most frequently at plate boundaries due to constant tectonic plate movement.
• This change can be slow, occurring over millions of years, or sudden and violent
• The area around the Pacific Ocean's plate boundaries, with many geological events like volcanic eruptions and earthquakes, is called the Pacific Ring of Fire.
• Plates moving together cause "subduction," where one plate slides beneath another, melting into the mantle.
• Moving apart cause "volcanos," and the plates crack erupting lava and hardening for form new rocks/crust.
• "Earthquakes" are caused by plates sliding past each other with a huge amount of friction in the plates makes them stick together. Pressure builds and then violent movements, earthquakes, happen.
• The size/magnitude of an earthquake depends on the plate boundaries size and how far the rocks move.
• Fold mountains are caused by rocks folding together from plates moving together.
• New fold mountains are between 10 and 25 million year olds while old ones are over 200 million years old.
• Volcanos are formed at the plate boundaries when magma rises through cracks in the Earth's crust and erupts to lava and ash.
• Magma is liquified rock underwater while lava is on the surface.
• If magma contains dissolved gas, the eruption is extremely violent.
• Active volcanos may erupt at any time while inactive are called dormant. Extinct volcanos cannot erupt again.

Shadows

• "Opaque is an object that that will not allow light to pass through. When an opaque object passes in front of a source of light then a shadow will form.
• Light travels in striaght lines called rays.

Eclipses

• A "solar eclipse" happens when the moon comes between the sun and earth.
• A "lunar eclipse" happens when the earth comes between the sun and moon.
• The moon orbits the earth in 27 days and is not exactly in the same plane and the orbit of the earth tilting it slightly.