How Light Makes Shadows Change Size and Direction

ShowIn the sunny courtyard, have students stand still and point to their own shadows. Ask, “Which side of your body is bright? Which side is dark?” Then ask them to notice whether the shadow is beside them, in front, or behind them. Students can point, gesture, or say their observations.

ConnectSay, “You found the dark place made when your body blocks light. The shadow is not stuck to your body. It is a place where light cannot reach. When the light comes from a different place, the blocked place changes too.”

ModelPlace the block between the flashlight and the wall. Say, “The block is the object. The flashlight stands for the Sun. The dark shape on the wall is the shadow.” Shine the flashlight from the left. Think aloud: “The light comes from the left, so the block stops light on its left-to-right path. The shadow appears on the opposite side, toward the right.” Move the flashlight to the right and show the shadow move left. Emphasize that the object stayed still, but the light source moved.

Worked exampleHold the flashlight high and shine it at the block. Point out the short shadow. Lower the flashlight while keeping the block in place. Point out the longer shadow. Say, “A low light makes a long shadow. A high light makes a shorter shadow. During the day, the Sun’s position in the sky changes, so a shadow can change size and direction.”

ConfrontAsk students to commit with a hand signal: “Will the shadow stay in the same place because it is stuck to the block, or will it move when I move the light?” Move the flashlight and have them check their prediction. Ask, “What moved, the block or the light?” Expected response: “The light moved, so the shadow moved.”

Check for understandingBefore moving the flashlight, ask students to point to where the shadow will go when the light moves from the left to the right. Ask one student to explain using, “The shadow moves because .”

TransitionIn pairs, one student holds the block at the marked spot while the other holds the flashlight. Partners switch roles after each test. The block represents an object outside, and the flashlight represents the Sun. Students make one change at a time and observe the shadow on the wall.

Have studentsFirst shine the flashlight from the left, then from the right. Next hold it high, then low. Each pair points to the shadow and tells a partner whether it became longer or shorter and which direction it moved.

ScaffoldKeep the two marked flashlight spots visible. Model the sentence frames orally: “The light came from .” “The shadow went .” “The low light made a shadow.” Students may answer by pointing, gesturing, or drawing a quick line with chalk rather than writing.

Look forStudents should say what they observed before explaining why. Listen for the misconception that the shadow is attached to the block. Ask, “Did the shadow move when the block moved, or when the light moved?”

ExtensionChallenge pairs to place the block closer to the flashlight and then farther away while keeping the wall in the same place. Ask them to compare the shadow sizes and explain how the object’s position also affects the shadow.

DiscussInvite two pairs to demonstrate one observation. Have the class complete the oral claim: “A shadow changes direction when , and it changes size when .” Expected response: “The light source changes position” and “the light is higher or lower, or the object changes position.”