Earthed

Why do planets that are closest to the sun orbit faster than the planets furthest away?

I am helping my daughter with a science project and would like to know specifically why planets that are closest to the sun orbit faster than further planets? I am having difficulty finding a specific explaination. Serious answers only. Thank you!

Public Comments

1. because they have to.. they would fail to be in orbit at a different speed
   
   
   
   to be in orbit requires that the grav force and the force required to keep a thing on a circular path is the same, too fast and it would fly off, too slow and it would spiral into oblivion. the closer they are together, the greater the gravitational pull, so it has to go faster to compensate
   
   
   
   GmM/r^2 = mw^2 r
   
   
   
   w is the angular frequency of the orbit (=2pi / planet year length in seconds), m and M are the 2 masses, r is distance between them and G is a constant (that i cant remember)
   
   the LHS bit is newtons law of gravitation, and the right hand side is the circular motion
   
   
   
   T = (4pi^2 GM/r^3)^-1/2
   
   
   
   T is year length. so if you assume that nothing changes but r, you can see that T is proportional to r^-3/2
   
   so T decreases as r increases
   
   i suppose the answer is that they have to
   
   the rest just shows why they have to from what we know about the things involved
2. Well the planet Mercury is closest to the sun, so they it has a shorter revolution around the sun. But Jupiter is way out in space as you know so it has a larger space revolutionize around the sun. Sorry never was that much into astronomy!!!
3. There are a combination of factors. One is that gravity is stronger closer to the sun. It's strength drops off with the square of the distance away from the source, so close in gravity is a LOT stronger than farther away.
   
   
   
   Also, planets near the sun have orbits that are smaller circles than those farther away. I takes longer to go around a longer path.
   
   
   
   I could go into the technical details of how Newton's laws of motion and gravitation give rise to Kepler's laws of planetary motion but I'll stop here for now.
4. There is more gravity pulling them in. Hopefully this helps.
   
   
   
   
   
   
   
   Thanx
   
   cc
5. since the planets closer to the sun are mostly little and there closer, they can travel way faster. mercury is the nearest so it travels the fastest orbit around the sun. as it the next planet behind has a bigger porbit because it further away.
   
   
   
   A TIP: pluto sometimes doesnt have the biggest orbit. neptune does. pluto's orbit is a ovel not round. it goes into neptunes orbit so NEPTUNE IS THE FURTHEST PLANET sometimes
6. If M is the mass of the Sun, m the mass of the planet and r the radius of its orbit then:
   
   
   
   GMm/r^2 = mv^2/r
   
   
   
   So v = sqrt(GM/r)
   
   
   
   and hence the further out a planet of the same mass is the lower speed it needs to stay in orbit.
7. Think of a Tether ball. The shorter the rope (closer the orbit), the faster it spins (to maintain it's orbit).