Question

activity c: planetary periods
get the gizmo ready: • click reset. • zoom out as far as possible. • set the speed to fast.
introduction: keplers third law describes the relationship between a planets orbital radius, or its mean distance from the sun, and the planets period, or amount of time to complete an orbit.
question: how does a planets orbital radius relate to its period?

1. predict: how do you think the period of a planet will change as its distance from the sun increases?
2. observe: click play, and observe the orbits of all the planets. what is the relationship between the speed of planets and their distance from the sun?
3. measure: click reset and zoom in as far as possible. click play, and then pause when earth is aligned with either the grids x - axis or y - axis. note the starting time below. then click play, and then click pause again when earth is in exactly the same position. note the ending time below.

starting time month: __ day: year: __
ending time month: __ day: year: __

1. calculate: what is earths period?

earth takes 12 months to complete an orbit, so earths period is 12 months, or one year.

1. measure: the distance units shown are the grid are called astronomical units (au). at earths orbit. how far is earth from the sun in au?

as you can see, one astronomical unit is equal to the mean earth - sun distance, which is approximately 150,000,000 kilometers.
(activity c continued on next page)

Explanation:

Step1: Based on Kepler's laws

As distance from the Sun increases, period increases.

Step2: Orbital - speed principle

Planets farther from the Sun have weaker gravitational pull, move slower.

Step3: Measurement - based task

Requires using the Gizmo tool for data collection.

Step4: Known fact

Earth takes 12 months to orbit the Sun.

Step5: Definition of AU

1 AU is the mean Earth - Sun distance.

Answer:

1. I think the period of a planet will increase as its distance from the Sun increases.
2. Planets farther from the Sun move more slowly.
3. This requires actual observation and measurement in the Gizmo, so no specific answer can be provided here.
4. 12 months or 1 year
5. 1 AU