echoes

• Echoes are created when sound waves reflect off surfaces
• Time delay between making a sound and hearing an echo is due to sound waves taking time to travel
• Speed of sound in air is 340 m/s
• Echoes can be used to measure distance by calculating the time it takes for sound to travel and reflect back
• Reverberation is when lots of echoes join together to produce a longer sound
• Ultrasound is sound above the frequency that humans can hear (>20,000 Hz)
• Ultrasound echoes are used in hospitals to make images of unborn babies, tumours, and injuries
• Sonar is a system for using echoes to detect underwater objects
• Force is measured in Newtons (N)
• Frequency is measured in hertz (Hz) or kilohertz (kHz)
• Loudness is measured in decibels (dB)
• Incident wave is the wave that is initially produced
• Reflection of a sound wave is when the wave bounces off an object
• Reflected wave is the wave that returns after reflecting off an object
• Soft walls and carpets can reduce reverberation (echoes)
• Most cinemas have carpets and soft coverings on walls to reduce echoes
• Ultrasound scans can be used to look at unborn babies, tumours, and internal injuries
• The speed of sound is 340 m/s, meaning sound travels 340 meters in one second
• Sound waves take time to travel, so there is a time delay between making a sound and hearing an echo
• Sound travels 1,500 m through water in one second
• Sound travels 3,400 m through air in 10 seconds
• Sound travels 180,000 m through water in 2 minutes
• It takes 2 seconds for sound to travel 10 km through a solid
• To hear an echo from a wall 1020 m away, it takes 3 seconds
• To hear an echo from a wall 2 km away, it takes 11.8 seconds
• A ship sends an ultrasound pulse to the seabed, and the echo is detected 3 seconds later, indicating the water depth
• If a ship's sonar detects an echo 1.5 seconds after sending the pulse, the water depth is 2250 m
• Ultrasound is sound with a frequency above 20,000 Hz
• Humans cannot hear ultrasound, although some animals can
• Goldfish use ultrasound to hunt
• Doctors can use ultrasound to make an image of an unborn baby (fetus) and check whether the baby is healthy
• Ultrasound waves pass through the woman and reflect off of the fetus
• The machine detects the echo
• It uses the time taken for the echo to be detected to calculate the distance to the baby’s features and with this information it can build up a picture
• Ultrasound scans can also be used to look for viruses in the body and to look at injuries
• Sound waves cause the eardrum to vibrate
• Ultrasound has a higher frequency than living things can detect
• The diaphragm on a microphone is a flexible plate which works in a similar way to the eardrum
• Loud sounds can damage your hearing
• Reverberation is where lots of echoes join together to produce a longer sound