Gravity and Space

Question 1

gravity

Answer 1

• An attractive force between 2 objects

- Acceleration due to gravity: 9.81 m/s^2

Question 2

strength of gravity depends on

Answer 2

• gravitational constant
• size of masses involved (density and volume)
• distance between masses (r)

Question 3

Changes in gravity: imagine a satellite circling a planet that is a uniform sphere

Answer 3

some gravitational force at the same distance from center of mass

Question 4

Changes in gravity: imagine a satellite circling a planet that is uniform material, but not perfect sphere

Answer 4

force of gravity is lower over large depressions and higher over high elevations

Question 5

Changes in gravity: imagine a satellite circling a planet that is a spherical planet, but not uniform material

Answer 5

• higher density materials = stronger force of gravity

- Ex. Mafic igneous rocks have higher density -> higher force of gravity

Question 6

Changes in gravity: imagine a satellite circling a planet that is a non-uniform body

Answer 6

have to divide it into pieces, calculate gravity from each piece, then add them up

Question 7

force of gravity at centre of earth

Answer 7

zero!

Question 8

why are gravity and topography somewhat related?

Answer 8

Elevation that could cause higher gravity is offset by isostasy

Question 9

isostasy

Answer 9

• Balancing act that prevents huge gravity anomalies on Earth
• Large masses won’t have huge positive gravity anomaly as the dense mantle below will be displaced on either side
• • Ex. Causes blocks of same mass but different densities to sink into mantle at same depth
• • Ex. Causes blocks of same density but different masses to sink at different depths

Question 10

isostatic equilibrium

Answer 10

• Mountains come into isostatic equilibrium through erosion -> roots of mountain rise as overlying rock is eroded
• Not all areas are in isostatic equilibrium yet (ie. Himalayas)

Question 11

isostatic equilibrium: oceanic vs. continental plate

Answer 11

Low density of continental lithosphere compensates for elevation -> same gravitational force on both blocks

Question 12

isostatic equilibrium: within a continental plate

Answer 12

“root” compensates for elevated continental crust (ie. Mountains)

Question 13

isostatic rebound

Answer 13

negative anomaly due to removal of ice sheet that once covered the area -> crust is still bouncing back (ie. Hudson’s Bay area)

Question 14

isostatic compensation (oceanic vs. continental)

Answer 14

Continental crust tends to be more elevated and thicker than oceanic crust in order to account for its smaller density

Question 15

measuring gravity

Answer 15

• Pendulums
• Weight vs. Spring
• Satellite orbital patterns (Mars, Venus, Earth)
• When reading gravity measurements, remember to check where the black line is -> our measurements can’t go any deeper than that line

Question 16

measuring anomalies

Answer 16

• GRACE (Gravity Recovery And Climate Experiment): 2 identical orbiting satellites, part of their job is to observe isostasy
• Wordon gravimeter: used to measure smaller anomalies, like variations over UBC’s underground library -> applications: indicate buried dense material, groundwater, etc.

Question 17

evidence for gravity and solar system formation

Answer 17

• Planets orbit in same direction (counter-clockwise)
• Orbits of planets are approximately in same plane
• Density of planets decreases away from the sun
• Terrestrial/rocky planets close to sun, Jovian/gassy planets farther away

Question 18

solar nebula hypothesis

Answer 18

• Cloud of dust and debris from supernova starts to contract and rotate
• Temperature in centre of cloud starts to increase and glow
• Gravity attracts particles together in surrounding disk (accretion)
• Accreted matter starts to form larger bodies (protoplanets)
• Pressures/temperatures increase, initating nuclear fusion -> our sun is born!
• Radiation from sun pushed lighter elements away -> only denser material is close to sun

Question 19

planetary formation

Answer 19

• Division between terrestrial and Jovian due to where they formed
• Close to the sun, lighter gases blown away -> gases condense beyond “snow line” to form Jovians

Question 20

formation of earth

Answer 20

• Following accretion – earth heats and differentiates
• Heavier elements sink to centre -> iron core (gravity)
• Initially a magma ocean

Question 21

All planets have ____ and all physical bodies _______

Answer 21

• gravity

- attract each other