Topic 3 Flashcards
What’s gravitational potential energy
By a body due to its height above the Earth
Depends on the mass of the body
The gravitational field strength
The height the body is raised
Gpe equation
Mass x gravitational field strength x change in height
Change in gpe = m x g x change in H
What’s kinetic energy
Stored in moving objects
How do you work out ke
1/2 x m x speed^2
What’s KE proportional to
Directly proportional to the mass of the moving object
Doubling the mass doubles the KE of moving object
Directly proportional to the square of the speed so doubling the speed means the KE increases by a factor of four
What do waves do?
Transfer energy and information without transferring matter
Evidence for this is water wave can be seen when a ball dropped into a pond bobs up and down but the wave energy travels outwards as ripples across the surface of the pond
What can waves be described by?
Frequency
Speed
Wavelength
Amplitude
Period
Examples of longitudinal waves
Sound waves and seismic P waves
How do particles move in longitudinal waves
In the material the sound is travelling through move back and forth along the same direction that the sound is travelling
Which way do they move in longitudinal waves
Move along the same direction of the wave
Examples of transverse waves
Waves on a water surface
Electromagnetic
Seismic S
How do the particles move in transverse waves
Move in a direction at right angles to the direction the wave is travelling
Move across the direction the wave is travelling
Both equations for speed
Speed = d/t
Speed = frequency x wavelength
What are the names of the two methods of calculating the speed of sound in air
Using an echo
Using two microphones and an oscilloscope
How do you use an echo
Measure distance from sound and reflecting surface (wall)
Measure time interval between sound and echo
Use speed = distance/time
How do you use a microphone and an oscilloscope
Set up microphone one in front of the other at different distances in a straight line from a loudspeaker
Set the frequency of the sound from the loudspeaker to a known audible value
Display the two waveforms on the oscilloscope measure the distance between the microphones
Move the microphones apart so that the wave forms move apart by 1 wavelength
Wavespeed = frequency x wavelength
What do u need to work out the speed of ripples on the surface of water
A ripple tank and a strobe
How do u use a ripple tank
Set power supply to vibrate the paddle at a known frequency the image of waves are on screen use a strobe light to freeze the water waves so that you can measure the wavelength
When a sound/light/water wave reaches the boundary between two materials it can be :
Reflected
Refracted
Transmitted
Absorbed
The amount of reflection that happens at a boundary depends on
The densities of the materials
Greater the differences in density the more sound energy will be reflected
When is sound transmitted through a material
Similar densities
When is sound absorbed by materials
Depends on the material and the wavelength of sound - amount of absorption
When is sound reflected
Big difference in densities of the materials at an interface for example between air and concrete
What can refraction result in
Change of both speed and direction
When does the direction not change in refraction
When the wavefront is perpendicular to the normal
When do sound waves travel slower
In cooler denser air
When do water waves travel faster
In deep water
What’s refraction in its special case
When light sound or water waves move from one material into another their direction does not change if they are moving along the normal
What’s the process used by the ear to detect sound
Waves producing vibrations in solids
Vibration and waves
When objects vibrate
Sound waves produces
Sound waves are a series of oscillations that transfer energy from the source to the ear
What range can human ear detect frequencies
20Hz-20kHz
Energy transfer is
When air molecules are forced to vibrate by the source of the vibration energy travels via a longitudinal wave until it reaches the ear
How does the ear detect sound
Sound waves are channeled down the ear canal and cause the eardrum to vibrate
These vibrations pass through the ear as further vibrations are then converted to N electrical signal and carried to the brain
Why can humans only hear sound in the range 20Hz to20kHz
Sound waves are travelling from air into a solid ate converted to vibrations and travel through the solid as a series of vibrations this conversion of sound waves to vibrations in solids only works over a limited frequency range
What’s ultrasound
Sound waves with a frequency above 20kHz
What’s infrasound
Sound waves with a frequency lower than 20Hz
Exploring the earths core
Infrasound is believed to travel through the earth as shockwaves from tsunami volcanoes or earthquakes
Infrasound is also produced when meteors enter the earths atmosphere
Scientists can detect this infrasound and track the path the meteor will take
Infrasound waves can be detected from explosions under the ground. The infrasound waves can also help to determine the structure of rocks beneath the earths crust
Pre-natal scans
Ultrasound waves make inside body images
Not harmful
Safe on foetuses
Ultrasound waves sent into woman’s body and some of sound is reflected each time it meets a layer of tissue with a different density to the one it has just passed through.
Scanner detects echoes and a computer used information to make a picture
Sonar
Sonar uses impulses of ultrasound to find the depth of water beneath a ship the sonar equipment measure the time between sending the sound and detecting its echo
What happens when a sound wave moves from one material to another
The wave speed or velocity may change
Wavelength may change
Frequency will not change
Wave speed = frequency x wavelength
Wavelength is directly proportional to
Wave speed
Density and speed of sound and n steel
7.86
5940
Density and speed of sound in water
1
1496
Densityband speed of sound in fat
0.94 and 1450
Density and speed of sound in muscle
1.06 and 1580
Density and speed of sound in air
0.00139
331
Speed of sound info
Speed of sound in a material usually depends on the density of the material
More dense more speed since wave can be passed more easily from particle to particle
