Which celestial body has the most influence on the Earth? (Universal Law of Gravity)

This activity can be done as a two part activity. Part 1 explores the universal law of gravity equation. Part 2 examines which celestial body in our solar system has the largest pull on the Earth.

Background

It took a little while, but humans eventually  figured out that the Earth does revolve around the Sun.  The Sun is so massive (literally meaning full of mass) that it doesn’t only hold the Earth in its orbit, but even small celestial objects like Pluto, hanging out an average of 3 billion miles away are kept in orbit.  

Below, check out how gravitational pull varies within our solar system from object to object (note: the theoretical ball “dropping” is all the same mass and the same distance away, to create a true comparison).

Click play below watch the video:

In this activity, you will be looking at mass and distance of five celestial objects.  What is a bit mind blowing is that even though the moon is discussed as being “close”, the distance between the Earth and moon is still large enough to fit every other planet between:

Use the following data set to explore how forces change as we manipulate different variables.

Dataset

This data set was gathered from https://nssdc.gsfc.nasa.gov/planetary/factsheet/ and https://www.theplanetstoday.com/gravitational_forces_of_the_planets.html

Variables

Mass (10^24 kg) - this numerical variable describes the amount of mass contained in the object.  Measured in 10^24 kilograms.

Distance to Earth (AU) - this numerical variable describes the distance between the object and Earth. Measured in Astronomical Units.

Force (10^15 N) - this numerical variable measures the gravitational force between the object and the Earth.  Measured in 10^15 Newtons.

Planet / Moon - this categorical variable names which celestial object is being discussed.

Activity

1. Make a prediction!  Below, the planets are shown in order of size, as well as distance to the earth:

Which planet or body do you think pulls on the Earth the most (remember, we are excluding the sun)?  Does distance or mass hold the most influence?

 2. Let’s explore some data.  Use the Make a Graph tool to create a bar graph for  Planet / Moon vs. Mass graph by showing Planet / Moon on X axis, and Mass on Y axis.  Screenshot your graph below:

Extension A:  While Venus, Earth, and the Moon look like they have similar values, their values are actually different.  By using a log transformation, we can more easily see the differences in these values all at the same time. Turn mass into a log scale and screenshot your new graph below:

(Question for both #2 and extension): What do you notice about the object with the most mass vs. the least? Is it a large difference?  What is the value of the mass of the smallest object?  (Hint: Float your mouse above Venus, Earth, or Moon to see their mass values).

3. Use the Make a Graph tool to create a bar graph for  Planet / Moon vs. Distance to Earth graph by showing Planet / Moon on X axis, and Distance to Earth on Y axis.  Screenshot your graph below:

Which object is the furthest and which is closest? Are the distance differences large? (Hint: Float your mouse above Venus, Earth, or Moon to see their distance values)

4. Lastly, make a graph of Planet / Moon vs. Force by showing Planet / Moon on the x-axis and Force on the y-axis.   Screenshot the graph below:

What surprises you about this graph? Discuss the value of the moon, but also look at the force of Jupiter and Venus on Earth as well.

5. Which variable, mass or distance, has the largest effect on gravitational force? Use the data from your graphs (#2, #4, #6) as evidence.

6. Relate your evidence you listed in #5 to the Universal law of Gravity equation.  How is your evidence further confirmed by this equation?

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