1. What is sound (1).pptx

SOUND WAVES Know how sound is created Be able to explain how sound travels in terms of particles What is sound? When something vibrates, it passes the vibrations into it’s surroundings (air) These vibrations create regions of space where the air particles are more bunched up an...

SOUND WAVES Know how sound is created Be able to explain how sound travels in terms of particles What is sound? When something vibrates, it passes the vibrations into it’s surroundings (air) These vibrations create regions of space where the air particles are more bunched up and others where they are more spread out. Vibrations cause the air particles to push together creating a compression (more dense) The particles then spread out causing a rarefaction Sound waves require air particles to transfer the energy so sound cannot travel through a vacuum  What is sound? Sound is produced when something vibrates, moving back and forth very quickly. But how does the sound reach our ears? Air molecules 1) An object 3) These makes a sound by 2) The vibrations pass through vibrations are vibrating air by making air molecules picked up by the vibrate ear What vibrates? What vibrates? What vibrates? What vibrates? What vibrates? What vibrates? What vibrates? Sound waves Sound travels in waves (waves made of vibrating air particles) These waves are the movement of alternating compressions and rarefactions. Sound waves travel away from the source of sound – like ripples of water that move outwards when a stone is dropped into a pond. Sound needs particles to travel – sound can pass through solids, liquids and gases. Sound waves are longitudinal Sound waves are longitudinal waves. In longitudinal waves, the particles move back and forth, so the direction of their movement parallel to the direction of the wave. What do longitudinal waves look like? A Slinky can be used to model longitudinal waves, by moving one end of the Slinky left and right. source moves coils vibrate left and right left and right direction of wave The wave travels away from the source. The direction of the wave is parallel to the movement of the source. In a longitudinal wave, the coils do not travel horizontally, each coil of the Slinky just vibrates left and right. What are the parts of a longitudinal wave? Certain parts of a longitudinal wave have special names. Sections that are pushed together are called compressions and that are stretched out are called rarefactions. compression rarefaction Sound waves are longitudinal waves. When someone speaks, the air particles vibrate as a longitudinal wave and so compressions and rarefactions are formed in the air. P waves, the primary waves produced by earthquakes, are also longitudinal waves, which push and pull the Earth. Simulation of a longitudinal wave Detecting sound When a sound wave strikes an object, it can cause the object to vibrate. The main way you detect or sense sounds is through your ears. The sound waves vibrate your ear drum, which goes to the inner ear and is changed to nerve signals you can sense. There are mechanical devices that detect sounds, such as the microphone. The sound vibrates a membrane, which creates an electric signal that is amplified and recorded. Sound does not travel in a vacuum because it requires particles in a medium to vibrate.  The speed of sound The speed of sound in air is 343 meters per second at one atmosphere of pressure and room temperature (21°C). An object is subsonic when it is moving slower than sound. Thunder and lightning, is an example that shows that sound travels slower than light. In air sound travels at: 343 metres per second. However light travels at: 300,000,000 metres per second. What happens when sound travels through other materials? Sounds cause particles to vibrate, this causes the sound to travel. Do you think a sound travels quicker in a solid, liquid or a gas? Think of reasons for your opinion and be ready to share. Copy and complete the sentences: Sound can travel at different ………………. depending on the …………………… it is travelling through. Sound travels faster in a ……………… than it does in a ………………. or ……………….. This is because the particles in a solid are …………………… together than they are in a gas. CLOSER SPEEDS LIQUID GAS MEDIUM SOLID  The speed of sound We use the term supersonic to describe motion at speeds faster than the speed of sound. A shock wave forms where the wave fronts pile up. The pressure change across the shock wave is what causes a very loud sound known as a sonic boom.  The Doppler effect The shift in frequency caused by motion is called the Doppler effect. It occurs when a sound source is moving at speeds less than the speed of sound. What do you know about the word: Ultrasound Help: what could the word mean? Try breaking it into two separate words. What is it used for? What do you know about the word: Ultrasound From the Latin: ultra. Meaning ‘beyond’. What do you know about the word: Ultrasound From the Latin: ultra. Noun. A thing that can Meaning ‘beyond’. be heard.  Ultrasound Frequency is measured in hertz (Hz). One hertz is when one thing happens in a second, but how does this relate to sound waves?  Ultrasound The frequency of a wave tells us how many waves pass a certain point in one second. Imagine a wave moving past a start point. Star End t  Ultrasound We can count how many waves there are between the start and the end to let us know how many moved in one second. In the space of 1 Star second, 11 End t completed waves have passed the start point, the sound wave has a frequency of 11  Ultrasound Humans cannot hear all sounds, we can only hear sounds that have a frequency between 20 hertz and 20,000 hertz.  Ultrasound Anything below 20 Hz is too low pitch for us to hear, and is known as infrasound. Anything above 20,000 Hz is too high pitch for us to hear, and is known as ultrasound. low frequency high frequency low pitch high pitch infrasound ultrasound  Ultrasound Not all animals have the same hearing range. Dogs can hear from 40 Hz to 40,000 Hz, a much higher range than humans. This means dogs can hear very high pitch noises from whistles.  Ultrasound As mentioned, different animals have different hearing ranges, some are shown below. 10 Hz 100 Hz 1 kHz 10 kHz 100 kHz 1 MHz Human 31 Hz to 19 kHz Dog 64 Hz to 44 kHz Cat 55 Hz to 77 kHz Mouse 900 Hz to 79 kHz Bat 10 kHz to 115 kHz Porpoise 75 Hz to 150 kHz Bats: Navigating with ultrasound Bats make high-pitched chirps which are too high for humans to hear. This is called ultrasound Like normal sound, ultrasound echoes off objects The bat hears the echoes and works out what caused them They navigate and find food using ultrasound Dolphins also navigate with ultrasound This is called echolocation Submarines use a similar method called sonar We can also use ultrasound to look inside things.  Ultrasound: Echolocation The boats use SONAR (Sound Navigation and Ranging). The boat sends out a pulse of ultrasound and detects the return wave. By knowing how fast sound travels and how long the wave takes to travel, we can calculate the distance from the boat to the sea bed.  Ultrasound: Echolocation The boats use SONAR (Sound Navigation and Ranging). The boat sends out a pulse of ultrasound and detects the return wave. If there are fish in the way then the time taken for the wave to return will be reduced.  Ultrasound: Echolocation The principle assumes the speed of sound to be 1500 ms-1, and the time taken is divided by two to get the distance to the sea bed. The sound wave takes 3 seconds to return to the boat. That means it took only 1.5 seconds to reach the sea bed (divide by two).  Ultrasound: Medical Uses A very important use of ultrasound is in medicine. It can be used to safely image the inside of the body, a safe alternative to x-rays.  Ultrasound: Medical Uses The image below shows the inside of the human heart with valves moving using ultrasound. It is a safe and easy way to look at whether there is a problem, and avoids unnecessary operations.  Ultrasound: Medical Uses The ultrasound waves can travel through soft tissues, but are reflected by more dense materials. This helps build up an image of the baby, using several reflections of ultrasound. Learning check What is ultrasound? Why cant humans hear ultrasound and what animals can? Why do we use ultrasound (name three uses)? Why is it advantageous to use ultrasound to check for underground pipes? Stile: 3.1 Lesson: Soundwaves