Sound – Part 1 Year 7 Science

What is sound Sound is a form of energy caused by vibrations. Put your hand on your throat and say something now! Feel the vocal cords in your throat vibrate as you make a sound. When sound travels through air the air particles are vibrating. This travelling vibration is called a sound wave. Therefore when you hear sounds vibrations are happening. In this case your eardrum is vibrating.

Sound needs something to travel in Since sound is a form of energy produced by vibrations it needs something to travel in that has particles that can vibrate. In air sound travels as the air particles vibrate. Sound can also travel in water. Next time you are at the swimming pool ‘shout’ to a friend while you are both under water. In this case the water particles are vibrating. Can sound travel through solid materials like glass and steel?

Sound in gases, liquids and solids, Yes, sound can travel through gases, liquids and solids. Particle Theory tells us that all these materials have particles and hence vibrations can happen. Can sound travel in a vacuum?

NO Sound cannot travel in a vacuum. Class, tell me why ??? And, what is the speed of sound…

Speed of sound The speed of sound in air at sea level altitude and at a temperature of 15 degrees Celsius is.. Speed of sound in air is 340 metres in a second or 1225 km per hour. Do you think the speed of sound is different for solids, liquids and gases? If so, why? Which is fastest?

Speed of Sound

Pitch The highness or lowness of a sound is called its pitch. The more quickly an object vibrates the higher the pitch. A short string vibrates more quickly that a long one and hence has a higher pitch. Pluck a string on a guitar! When you blow across the top of a pan pipe the air inside it vibrates. The shorter the pipe the faster the air vibrates and the higher the pitch (teacher demonstrates). We will do some fun experiments on pitch this week

So what is Frequency ?? We sometimes hear the term frequency. What does frequency mean??? Frequency means how often something happens. For things that happen very quickly, frequency is measured in hertz. If you blink your eyes very quickly say 5 times a second, the frequency of your eyes blinking is 5 hertz.

So how does frequency relate to pitch? With sound, changes in frequency change the pitch of the sound. Low-frequency deep sounds like trucks rumbling along a road or the rumble of thunder have a low pitch sound. High-frequency sounds like a dentists drill or a whistle have a high pitch sound.

Range of frequencies we hear Our range of hearing is from approximately 25 hertz to 20,000 hertz. It varies from person to person and how old you are. Sounds that have a frequency below 25 hertz are often just ‘felt’ rather than heard. Like the rumble of thunder. Sounds above 20,000 hertz are often not heard at all. But dogs can hear these sounds – like when you blow a dog whistle. And bats can make sounds as high in frequency as 150,000 hertz !!!

A Sound Spectrum

Homework: Due 15 th August 2006: Read Experiments 9.7and 9.8 on page 184 of Core Science 1 text and write an Aim, Equipment List and Method for each experiment. Due 18 th August 2006: Write an explanation of your results and conclusions for both experiments 9.7 and 9.8 that you performed on Tuesday 15 th August. Read pages of Core Science 1 text and answer all Remember and Think Activities on page 185. OPTIONAL HOME EXPERIMENT TO CONDUCT Home experiment: Conduct the “straw clarinet” experiment shown in the handout and write a brief explanation of your findings.