6.5 hsw what lies beneath
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Transcript of 6.5 hsw what lies beneath
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6.5 HSW: What lies beneath?28 January 2015
What is the difference between mass and
weight?
Quantity Symbol Unit Unit symbol Description
Mass
Weight
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Quantity Symbol Unit Unit symbol Description
Mass m kilogram kg Amount of stuff
Weight W newton N Gravitational pull on amount of stuff
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Quantity Symbol Unit Unit symbol Description
Mass
Weight
Quantity Symbol Unit Unit symbol Description
Mass
Weight
Quantity Symbol Unit Unit symbol Description
Mass
Weight
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Gravity map
• You may think that the force of gravity of the Earth is the same all over the Earth but it isn’t
• At the Earth’s surface, the Earth pulls object towards its centre with a force of 9.8 N on every kilogram of mass (9.8 N/kg)
• Another way is saying that one kilogram will accelerate by 9.8 m/s every second (9.8 m/s2)
• This value can change depending on where you are standing and what you are standing on
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Gravity surveys
• Rocks are made from different materials.
• Some are made of sand while others contain denser material like iron
• A dense materials is one which is heavy for its size
• Think of a block of iron compared with a block of polystyrene. When you stand on the rock with iron you are pulled down more strongly than where you are standing on rock made of sand
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Gravity surveys
• Geologists carry out gravity surveys to investigate these differences in gravitational attraction
• They use a spring with a mass on the end to measure the gravitational attraction in each place
• This is called a gravimeter
• The stronger the force, the more the spring stretches
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Hidden secrets
• Gravity surveys help us work out what is below the surface without having to dig or drill
• They can reveal underground springs, rivers and volcanic bases as well as evidence that the Antarctic ice sheet is losing ice
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Examples
• Geophysicists:
– Look for underground rock movements that might show an earthquake is about to occur
• Oceanographers
– Look for changes in ocean currents and climate
• Archaeologists:
– Look are remains of walls and buildings to help inform them of where to investigate
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The view from space
• Satellites can now measure gravity variation from Space to produce gravity maps like the one of the Earth
• The red parts are areas of high gravity
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Experiment: Determine the value of g graphically?
• You have a number of different masses
• Weigh the masses using a newton meter
• Draw a table for your results
• When you have collected all the data (including repeats) construct a graph
• Determine g
Mass / kg Weight / N0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
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0
1
2
3
4
5
6
7
8
9
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
We
igh
t /
N
Mass / kg
A graph to determine value of g
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0
1
2
3
4
5
6
7
8
9
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
We
igh
t /
N
Mass / kg
A graph to determine value of g
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0
1
2
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9
10
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
We
igh
t /
N
Mass / kg
A graph to determine value of g on Earth
kgNg
kg
Nm
mass
weightm
massmweight
mxy
cmxy
10
1
10
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Questions
• A block of iron and a block of polystyrene are the same size
– Which block has more mass?
– Which provides a greater force of gravitational attraction?
(4)
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Questions
• The force on a 1 kg block at the Earth’s surface is on average 9.8 N
– What is the force on a 50 kg pupil?
– What are the weights of the block and the pupil?
(5)
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Question
• Suggest why scientists use colours rather than numbers on the map to represent changes in gravity. (qualitatively)
• What is the advantage of presenting the data numerically? (quantitatively)
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Questions
• Create a key to go with the gravity map of Antarctica
• Suggest which colours should represent medium, low and very low gravity areas.
(7)
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Question
• As well as showing areas of high density, gravity maps also show the locations of mountains and valleys. Why would a mountain appear different to a valley?
(8)