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# Discovering Gravity – An Apple or an Airplane?

This post was written by Lesley Anderson, 2021-2022 Albert Einstein Distinguished Educator Fellow at the Library of Congress.

Newton’s Laws are one of the most important topics covered in a physics class. Newton’s Law of Universal Gravitation is typically introduced through a hands-on demonstration by dropping a ball or by discussing students’ past experiences with gravitational forces. This primary source offers an alternative way to introduce or reinforce this concept through a historical perspective.

First, ask students to list what they know or believe to be true about how Newton discovered gravity. Then, show students this image, and allow plenty of time for them to look closely. Encourage them to write down all of the details they see, any thoughts they have about the image, and anything they are wondering. Organize them to share their thoughts with a partner.

Prompt them to consider:

• Who are the men in the cartoon?
• Whose plane is in the tree?

Ask students to draft questions they have about the picture that relate to Newton’s Law of Universal Gravitation.

Encourage students to read the text at the bottom of the image, “It was an airship, and not an apple as popularly supposed, that gave Sir Isaac Newton his clue.” Allow time for them to consider what the text adds to their understanding. Next, support students in using context clues to identify Sir Isaac Newton, a 17th century natural philosopher, in the foreground of the cartoon. In a physics classroom, this is a great opportunity to introduce Newton’s Law of Gravitation.

Students may use context clues from the image, like the date of publication, to deduce that the plane in the tree is the Wright brothers’. They may learn more about the Wright brothers by exploring this blog post, this narrative of First Flight, or this primary source set.

What is the cartoonist implying about the connection between these two historic events? Facilitate a class discussion to uncover the overlaps between Sir Isaac Newton and the Wright brothers. Direct students to read in their textbook or other resources to learn more about Newton’s Law of Gravitation and how it applies to aerodynamics.

After you try this new historical introduction to Newton’s Law of Gravitation and how it was perceived in the early 20th century, you might extend the activity by bringing the Wright brothers together with another one of Newton’s Laws. Give students a picture of the Wright brothers’ plane and ask them to draw a free body diagram using arrows indicating the forces of Newton’s Third Law applied to aerodynamics, which indicates that for every action there is an equal and opposite reaction. Encourage students to indicate drag, lift, weight, and thrust on their diagram and be prepared to engage in a group discussion about which forces need to be increased in order for an aircraft to become airborne.

What can your students discover by bringing these innovators together across the centuries? Let us know in the comments.