Topic 7- Astronomy Flashcards
Why does the weight of objects change on different planets? e.g the Earth and the moon
- As F =G(mass1 x mass2)/Distance ^2
- G is a constant 6.674
- Meaning an object with LESS MASS (the moon) will have a SMALLER GRAVITATIONAL force (than the earth)
- As Weight= Gravitational field strength x mass
- An object on the moon (with the same mass) will weigh less
What is the gravitational field strength of the moon?
- 1.6 N
What is the gravitational field strength of the Earth?
- 9.8 N
- 10N
What is the (our) solar system made of?
- The sun
- Eight planets
-Dwarf planets - Natural sateleits (moons, asteroid, comets)
What are the names of the planets in order?
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
- (Pluto, dwarf)
How have ideas surrounding the solar system changed over time?
Geocentric- idea that the Earth was the centre of the solar system, and the sun, moon and planets orbited
Heliocentric- Idea that the sun is at the centre of the solar system, that the planets orbit it, and moons orbit the planets
What did the geocentric model not prove?
- Why planets changed brightness ( because they are not always the same distance from Earth)
- Jupiter and mars appeared to move backwards sometimes
- Why moons seemed to orbit planets (not everything orbited the Earth)
What in our solar system have a circular orbit/ slightly elliptical?
- Moon
- Planets
- Asteroid
What in our solar system have a highly elliptical orbit?
- Comets
Low Earth orbits: Height, speed, time to orbit, use
- 160 Km -> 2000km above Earth’s surface
- 7780 m/s
- 1.5/2 hours to orbit
- ISS (international space station)
- Communications
Polar Orbit: Height, speed, time to orbit, use
- About 160- 2000km above Earth’s surface
- 7500 m/s
- 1.5 hours
- Goes over poles
- Monitors weather, used for spying/image taking
Geo-stationary: Height, speed, time to orbit, use
- 35,900 km above Earth’s surface
- 3000 metres/s
- 24 hours
- Communications, television, weather
Elliptical: Height, speed, time to orbit, use
- Faster closer to the Earth
- Communications
How does a circular orbit due to gravity mean change in velocity but not speed?
- Gravity acts as the CENTRIPETAL force keeping the object in a circular orbit (changes linear direction)
- Velocity is a VECTOR quantity and changes as DIRECTION CHANGES
- Speed is a scalar quantity
What is the equation for the (centripetal) force in a circular motion?
F= mv^2/ radius
Explain how, for a stable orbit, the radius must change if
orbital speed changes (qualitative only)
What happens when the radius changes in a stable orbit (same centripetal force)?
- As f=mv^2/r
- If the velocity changes, but the mass and force remain constant
- Radius must change to keep the constant
- If speed increases, radius must increase
- If speed decreases, radius must decrease.
What happens when the speed of a satellite decreases?
- Falls out of orbit, towards the centre (Earth) by gravity
- Gains speed when accelerating towards the Earth
- Stabilises as speed begins to increases and radius decrease for the F and M to be constant (F=mv^2/r)
Do objects in a lower orbit feel more gravity?
- Yes
- Lower radius means the object feels more gravity and therefore has to move faster
What happens if a satellite is moving too fast?
- Force of gravity cannot keep it in circular motion as it is too fast
- Moves off into space
- 11,200 metres/sec
Why are v and r always inversely proportional?
not for centripetal force
- Force felt= g(m1xm2)/r^2
- Force= mv^2/r
simplified
v^2= g(m1, the larger body’s mass)/ r
Therefore if v is to increase, r has to decrease as gravity (6.67) and mass are constant
What in the equation F=mv^2/r changes when radius increases?
for centripetal force
- V and R are directly proportional ( v^2= g(6.67) x m1/ radius
- When Velocity increases radius has to increase
- meaning force felt is NOT CONSTANT
- F also DECREASES.
Steady state: How the world began, Expansion, Density
- Always existed
- New matter is created by expansion
- Density remains the same as new matter (mass) is being created at the same rate of expansion (volume)
Big bang: How the world began, Expansion, Density
- All universe (abt 14 billion years ago) was a very small and dense region which exploded
- Explosion caused rapid continuous
expansion - Density decreases as no new matter (m) is created but the universe (v) is expanding
