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Name: Jason
Status: student
Grade: 3-5
Location: NJ
Country: USA
Date: Summer 2012

My question involves the inertia and gravity of comets and asteroids. I am going to ask in layman terms since it has been a while since I graduated college. My son is 8 and he has been asking me very good questions that I cannot answer nor can his 3rd grade teacher. Here it goes: How do comets and or asteroids get knocked out of the Oort cloud, Keiper Belt or asteroid belt? When the force is exerted onto them and gives them a push, and then they start falling into our solar system at the sun, how is it that they actually go around the sun and head back away from the sun, only to make the turn again to become in orbit with the sun? Are all of the comets and asteroids that orbit the sun, doomed to fall into the sun at some point eventually? Is the sun's gravity so strong that it would actually pull the comet or asteroid right into it? I know I asked a bunch of questions in one, but they all have to do with the orbits of them. I do not know how to explain this to my son, and I want to know as well. What initiates the space rocks first orbital path, and how does it miss the sun?

Hi Jason, It might help if your son discovers the answers through play. Try this simple simulation:

It shows how the interplay of mass, inertia (or momentum, or velocity), play on the effects of gravitational forces.

We can use Newton's first law (an object that is in motion will stay in that motion until a force acts on it) to explain object trajectories. So an object that is in motion is affected by the gravitational force of the Sun (and other massive objects in the system), and these combination of forces can either make the object crash into others, form stable orbits, or get ejected out of the system.

Greg (Roberto Gregorius) Canisius College

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