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?

Time for each orbit

Radius

Earth 1.00 1.00

Mars 1.52 1.88

Jupiter 5.20 11.9

Saturn 9.53 29.5

Important:The orbits on this slide are not shown to scale!

(AU) (years)

0.240.39Mercury

Venus 0.72 0.61

P3 1.7 Planetary orbits

What does this data show?

Speed = dist R time T

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

Force of gravity on planet

sun

Earth R = 1 AU T = 1 Yr

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

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

sun

Earth R = 1 AU T = 1 Yr

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

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

sun

speed = dist (2πR) time (T)

speed = 2 π1 1

AU/yr

Earth R = 1 AU T = 1 Yr

P3 1.7 Planetary orbits

The larger the orbit the slower the speed and the longer it takes

Velocity of planet

Force of gravity on planet

sun

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

Force of gravity on planet

sun

The speed is less because gravity is weaker when further away.

Saturn R = 9.53 AU T = 29.5 yr

P3 1.7 Planetary orbits

Velocity of planet

Force of gravity on planet

sun

Orbit time is longer because the planet has further to go and it is moving slower.

The larger the orbit the slower the speed and the longer it takes

Saturn R = 9.53 AU T = 29.5 yr

P3 1.7 Planetary orbits

Velocity of planet

Force of gravity on planet

sun

Orbit time is longer because the planet has further to go and it is moving slower.

The larger the orbit the slower the speed and the longer it takes

speed = dist time

Saturn R = 9.53 AU T = 29.5 yr

P3 1.7 Planetary orbits

Velocity of planet

Force of gravity on planet

sun

Orbit time is longer because the planet has further to go and it is moving slower.

The larger the orbit the slower the speed and the longer it takes

speed = 2 π 9.59 29.5

speed = dist time

speed = 0.65 π

AU/yr

Saturn R = 9.53 AU T = 29.5 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.