## Exploring our world: How does sound travel?

How does sound travel? Does sound travel differently than light? The Michigan State University Extension science team’s goal is to increase science literacy across Michigan. One way we increase interest in science is to provide information and ideas for engaging youth in the exploration of their world. Adults can help youth increase their science literacy by encouraging them to ask questions and discover answers. Exploring sound is just one way to engage youth in STEM (Science, Technology, Engineering and Mathematics).

Ask youth how they think sound travels. Does it travel the same way light does? Why or why not? Provide youth with a piece of rope and challenge them to make a wave by moving one end of the rope while the other end is stationary by being tied to a nail or doorknob. Youth should shake one end of the rope making an “S”-shaped wave that travels the length of the rope. Ask youth if the wave travels in the same direction as the movement used to make it.

Tie a colored ribbon at one point in the rope. Notice how the ribbon moves up and down, but not forward and backward on the rope. As they watch the wave, youth should realize that while they are shaking the rope up and down, the wave they create is traveling away, perpendicular to their motion—not up or down. This is a transverse wave; a wave that undulates perpendicular to the direction of propagation. Light waves are transverse waves.

Next, give youth a large spring, like a slinky, and have them stretch it out along a table. Ask them to make a wave without shaking it like they did the rope. Youth should discover they can make a wave in a spring by compressing, or pinching, a couple of the coils together then releasing them. Ask youth if the wave travels in the same direction as the movement used to make it. As they watch the wave, they should realize the wave they are making is traveling in the same direction as the motion they used to make it. This is a compression wave; longitudinal or compression waves undulate in the direction of propagation. Sound waves are compression waves.

While sound and light travel in similar ways as waves, do they travel similarly through the same types of matter? Ask youth to brainstorm and make a list of things sound can travel through. Help ensure they think about the three states of matter: solid, liquid and gas. Next, ask them to decide which of the items listed light can travel through. For more information about how sound travels through different materials read, Can you hear better underwater?

What about in outer space? Do you think light travels through outer space? Why or why not? Do you think sound travels through outer space? Why or why not? Youth should discover that sound waves can travel through more materials than light waves. Light waves or transverse waves can travel through the vacuum of space while sound waves or compression waves require a medium in which to travel.

Ask youth what they think travels faster: sound or light. Why do they think one is faster than the other? Can they recall evidence, something they’ve seen or heard, that makes them think the way they do? Allow time for youth to discuss their ideas and evidence.

Give one youth a metal cookie sheet and stick. Have them take the sheet and stick across a field or down a long driveway, about 100 yards away. Ask the youth with the cookie sheet to hold their arms straight out from their sides, cookie sheet in one hand and stick in the other. Next, bring their hands together over their head, strike the cookie sheet and bring their arms down again. Did the youth see the arms come back down before they heard the sound?

MSU Extension and the Michigan 4-H Youth Development program help to create a community excited about STEM (Science, Technology, Engineering, and Mathematics). 4-H STEM programming seeks to increase science literacy, introducing youth to the experiential learning process that helps them to build problem-solving, critical-thinking and decision-making skills. Youth who participate in 4-H STEM are better equipped with critical life skills necessary for future success.

To learn more about the positive impact of Michigan 4-H youth in STEM literacy programs, read our 2016 Impact Report: “Building Science Literacy and Future STEM Professionals.”

To learn more about MSU Extension, visit the MSU Extension website. To learn more about 4-H and Extension opportunities in Alcona County, stop by our Harrisville office at 320 S. State St. Harrisville, MI 48740, or visit us online at our Alcona County MSU Extension Facebook page or Alcona County Extension office page.