STEM Activity: Batty for Sound

Have you ever wondered how bats find insects to eat as they move through the night sky? They use echolocation! As they hunt, bats send sound waves out into the air. When the sound waves bounce back, bats use the information from the echoes to sense nearby objects.

With this STEM activity, you can turn on your batlike senses as you experiment with different materials and observe which ones are best for bouncing sound waves.

Materials Needed

• Bouncy ball
• Box or container (e.g., shoe box or aluminum steam pan)
• Crafting supplies (e.g., construction paper, fabric, foam sheets, rubber bands, yarn)
• Recyclable items (e.g., aluminum foil, bubble wrap, cardboard, plastic bottles)
• Tape

Step-by-Step Instructions

1. Find a bouncy ball and imagine that it represents a sound wave.
    
2. Grab your box or container and roll the ball toward the side of it, observing how it ricochets, or bounces. Listen to the sound it makes.
    
3. Next, tape different crafting supplies or recyclable materials to the inside of the box. Roll the ball toward each of these materials and observe what happens.
    
4. Think about the following questions:
   • Which materials stopped the ball from bouncing?
   • Which materials softened the bounce, but didn’t stop it completely?
   • Which materials increased the ricochet?
   • Did the sound of the ball’s movement inside the box change with the different materials? How so?
      
5. Try to turn your box into the ultimate ricochet machine that will allow the ball to bounce off each of its sides. Experiment with which materials, or combinations of materials, allow for the most ricochet action.

What Are We Discovering?

Echolocation is the ability to locate objects by making sounds and listening to how the sound waves bounce back off of objects. Moths, which bats prey on, use a very erratic flight pattern to interfere with the bat's echolocating ability.

Radar and sonar technologies were developed in part by studying how bats and other animals use sound waves to locate objects and navigate. Radar, which uses radio waves, and sonar, which uses sound waves, are very useful for detecting objects in locations or conditions that make the objects hard to see. Like echolocation, the radio waves and sound waves that bounce off of objects provide a lot of valuable information about that object, like the type of material and its size, shape and density.

Hard surfaces like tabletops, concrete and wood floors do a good job of sending sound waves back into the air to bounce around more and help us to hear them. Soft surfaces absorb, or collect, some of the energy in the sound waves and do not send all of them back into the air. That is why softer objects tend to block sounds, making them quieter, and hard objects help the sound bounce around and stay louder.

National Inventors Hall of Fame^® Inductee Wallace Sabine, a physicist, created the field of architectural acoustics. Acoustics is the study of the science of sound. Sabine completed experiments to determine how the size of a room and the types of surfaces within it affected a room’s acoustics. Using what he discovered, he incorporated sound-absorbing materials throughout large spaces. This helped increase a room’s acoustics by cutting down the reverberation time, reducing the “echo effect.”

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