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30 Cards in this Set
- Front
- Back
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the bigger the vibrations when an object or substance vibrates, the ___ |
the greater the amplitude and louder the sound |
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what can detect reflected ultrasound waves |
a detector |
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why are some ultrasound waves partly reflected back |
when they reach a boundary between two substances with different densities |
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what does a detector do |
it measures the time between an ultrasound wave after leaving the source to reach the detector |
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what can ultrasound be used for |
in industry for quality control procedures to check manufactured objects like railway tracks for damage or defects in pre-natal scannings sonar |
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how do computers create detailed images in ultrasounds |
by combining many ultrasound reflection readings |
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how is ultrasound used in sonar |
a pulse of ultrasound is sent out from the ship. it bounces off the seabed or shoal of fish and the echo is detected. the time taken for the wave to travel indicated the depth of the sea bed or fish |
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how is infrasound detected |
using a microphone |
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how do scientists track herds in dense forests |
they use microphones which helps with the protection of the animals |
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what else can infrasound detect |
volcanic eruptions and the passage of meteors |
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why is gel used in ultrasounds |
the gel is applied as a contact medium between the tissue (skin) and the ultrasound head. it conveys the sound waves from the ultrasound head to the tissue without passing through the air at any point. this is because the reflection is less when crossing from a gel to body tissues than air to body tissues |
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what is the earths crust like |
thin and rocky |
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what is the earths mantle like |
properties of a solid but can flow very slowly |
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what is the earths outer core lkke |
made from liquid nickel and iron |
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what is the earths inner core lkke |
made from solid nickel and iron |
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what are the tectonics plates made from |
the earths crust and upper part of the mantle |
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what is continental drift |
the plates move a few centre metres each year. over millions of years the movement lows the whole continents to shift thousands of km apart |
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why do the plates move |
because of convection currents in the earths mantle. these r driven by the heat produced by the decay of radioactive elements and heat left over from the formation of the earth |
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how do earth quakes occur |
An earthquake is the shaking and vibration of the Earth's crust due to movement of the plate tectonics. Earthquakes occur when tension is released from inside the crust. Plates do not always move smoothly alongside each other and sometimes get stuck. When this happens pressure builds up. When this pressure is released in a sudden jerk the earth quake occurs |
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why is it difficult to predict when an earth quake may happen |
because it is not possible to measure the forces trying to move plates or friction between them so you don't know when the sudden movement will happen |
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what is the focus |
the place inside the earth where rock suddenly moves |
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what is directly above the focus |
the epicentre |
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what instrument detects seismic waves |
seismometer |
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how do tsunamis occur |
if the earth quake happens under the sea the movement of the sea floor may cause a huge wave called a tsunami |
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how are tsunamis detected |
tsunami warning systems include pressure sensors that detect them |
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properties of P waves |
travel through solids and liquids longitudinal travel faster than S waves |
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properties of S waves |
travel through solids slower than P waves transverse |
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when can the path of a seismic wave have a kink |
when the properties change suddenly, the wave speed changes abruptly and the path had a kink |
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why do seismic waves change speed |
as the properties of the mantle and core change- the change in speed causes the waves to change direction which is refraction |
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how to detect earthquakes |
by using info from three seismometers you can calculate the epicentre which is where all three distanced meet which is triangulation. u calculate the time difference between the arrival of the S waves and P waves |
