Transcript P3 1.7 Planetary orbits

P3 1.7 Planetary orbits
Learning objectives
Be able to explain that;
1. The force of gravity provides the centripetal force
that keeps planets and satellites moving in their orbits.
2. To stay at a particular distance, a planet must move
at a particular speed around the sun.
3. The larger the orbit the slower the speed and the longer it takes.
If the Earth’s orbit were more elliptical, how would we be affected?
P3 1.7 Planetary orbits
Speed = dist
time
R
T
Radius
Time for each
orbit
(AU)
(years)
Mercury
0.39
0.24
Venus
Earth
Mars
0.72
1.00
1.52
0.61
1.00
1.88
Jupiter
Saturn
5.20
9.53
11.9
29.5
Important:
The orbits on this slide are not
shown to scale!
What does this data show?
P3 1.7 Planetary orbits
To stay at a particular distance, a planet must move
at a particular speed around the sun.
Velocity of planet
Earth R = 1 AU
T = 1 Yr
sun
Force of gravity
on planet
P3 1.7 Planetary orbits
To stay at a particular distance, a planet must move
at a particular speed around the sun.
Velocity of planet
Earth R = 1 AU
T = 1 Yr
sun
Force of gravity
on planet
If its speed is too slow, it will spiral into the sun
If its speed is too high, it will move away from the sun
P3 1.7 Planetary orbits
To stay at a particular distance, a planet must move
at a particular speed around the sun.
Velocity of planet
Earth R = 1 AU
T = 1 Yr
sun
Force of gravity
on planet
speed =
dist (2πR)
time (T)
speed = 2 π1
1
If its speed is too slow, it will spiral into the sun
If its speed is too high, it will move away from the sun
AU/yr
P3 1.7 Planetary orbits
The larger the orbit the slower the speed and the longer it takes
Velocity of planet
sun
Force of gravity
on planet
Saturn R = 9.53 AU
T = 29.5 yr
P3 1.7 Planetary orbits
The larger the orbit the slower the speed and the longer it takes
Velocity of planet
Saturn R = 9.53 AU
T = 29.5 yr
sun
Force of gravity
on planet
The speed is less because gravity is weaker when further away.
P3 1.7 Planetary orbits
The larger the orbit the slower the speed and the longer it takes
Orbit time is longer because
the planet has further to go
and it is moving slower.
Velocity of planet
sun
Force of gravity
on planet
Saturn R = 9.53 AU
T = 29.5 yr
P3 1.7 Planetary orbits
The larger the orbit the slower the speed and the longer it takes
Orbit time is longer because
the planet has further to go
and it is moving slower.
Velocity of planet
Saturn R = 9.53 AU
T = 29.5 yr
sun
Force of gravity
on planet
speed =
dist
time
P3 1.7 Planetary orbits
The larger the orbit the slower the speed and the longer it takes
Orbit time is longer because
the planet has further to go
and it is moving slower.
Velocity of planet
Saturn R = 9.53 AU
T = 29.5 yr
sun
Force of gravity
on planet
speed =
dist
time
speed = 2 π 9.59
29.5
speed = 0.65 π
AU/yr
P3 1.7 Planetary orbits
Elliptical orbits:
The squashed circle orbit
has two ‘foci’ F1 & F2
Distances
OF1 + OF2 = constant
The sun is at one focus
of the ellipse
P3 1.7 Planetary orbits
Q
P3 1.7 Planetary orbits
Learning objectives
Be able to explain that;
1. The force of gravity provides the centripetal force
that keeps planets and satellites moving in their orbits.
2. To stay at a particular distance, a planet must move
at a particular speed around the sun.
3. The larger the orbit the slower the speed and the longer it takes.