Making Waves with a Slinky

Grade Level: 4th-8th grade
Time Required: 30-50 Minutes
NDT Focus Area: Ultrasonic Testing (UT)

Students will understand the difference between different waveforms using a slinky as a model.

Download Handout

Learning Objectives

By the end of this activity, students will be able to: 

  • Demonstrate transverse, longitudinal, rotational, circular, Rayleigh, and torsional waves with a slinky.

  • Relate mechanical wave motion to sound waves and NDT applications.  

Key Concepts 

  • When a wave is present in a medium (that is, when there is a disturbance moving through a medium), the individual particles of the medium are only temporarily displaced from their rest position.

  • There is always a force acting upon the particles that restores them to their original position.

  • Different types of sound waves are better suited to inspect different materials, or to find specific types of discontinuities.

  • The time it takes for an echo to return to the technician shows the technician where the discontinuity is, and the amplitude of the returning wave shows them the size of the discontinuity.

Vocabulary

Here are some key terms you will need to know to support your understanding during the experiment.

Transverse wave

Motion perpendicular to direction of travel.

Longitudinal wave

Motion parallel to direction of travel (compression wave).

Rayleigh wave

Seismic surface wave with elliptical particle motion.

Torsional wave

A twisting wave motion.

Restoring force

A force that brings a displaced particle back to its equilibrium position.

Discontinuity

A flaw or irregularity in a material.

Materials Needed

Before you start, collect the following items for the experiment.

Slinky

Partner

(or fixed object like a chair)

Electronic device to access video

View Wave Models Video

Experiment Procedure

Follow these steps one at a time to carry out the experiment. Read carefully and take your time to make sure you complete each part safely and correctly.

Stretch the slinky 6 feet or more between two people, or tie one end to a fixed object.

Pull the slinky upwards (towards your face) and then push it down.

  • Observe a wave traveling along it.

  • The up–down motion creates a transverse wave.

Two people stretching a large slinky in an office, an up and down arrow indicating motion of the slinky..

Move your hand side to side while the slinky rests on a table to model horizontal polarized waves.

A hand holding a slinky stretched across a white table, with a blue arrow pointing showing the sideways motion put on the slinky.

Move your hand forward and backward while the slinky rests on a table to create a longitudinal (compression) wave.

Person demonstrating wave motion with a slinky on a white table, showing a blue arrow indicating direction.

Combine forward/backward and up/down motions to create circular motion waves (like ocean or Love waves).

Two people demonstrating a Slinky toy's movement across a room with blue arrows showing the circular motion on the slinky..

Rotate your wrist to send a torsional wave (like twisting in a violin string).

A person demonstrating a spring's motion on a white table, with blue arrows indicating rotational movement.

Expected Observations 

Transverse waves move perpendicular to the slinky length.

Longitudinal waves compress and expand along the slinky.

Circular and rotational waves combine motions.

Rayleigh waves demonstrate elliptical motion, possible only in solids.

Torsional waves twist along the slinky.

Real-World Connection:
NDT & Ultrasonic Testing

NDT technicians use ultrasonic waves to detect discontinuities in things like pipelines, airplane parts, welds, and train tracks. The time it takes for an echo to return indicates location of a flaw, while the amplitude indicates its size. Different types of waves travel differently through materials, making some better suited for certain inspections.

Learn More About Ultrasonic Testing
A technician performing an ultrasonic testing inspection on a large welded pipe. The technician is using a handheld transducer connected to a portable ultrasonic testing device with a screen displaying data. The setting appears to be outdoors, with industrial structures visible in the blurred background.

Apply What You've Learned

  • Draw diagrams of the waves demonstrated with the slinky.

  • Relate how ultrasonic testing uses waves to find flaws in materials.

Explore Where NDT Can Take You

You’ve seen nondestructive testing principles in action. Now discover the people, careers, and industries that make NDT an essential and exciting field.

Webpage

Applications Across Industries

Learn how NDT is applied in aviation, energy, construction, and other critical industries that keep our world moving safely.

Read More
Webpage

Explore Career Pathways

Learn about the different career routes available in NDT, from entry-level opportunities to advanced specializations.

Read More
Webpage

Jobs of Tomorrow Docuseries

Explore how NDT is transforming industries and creating opportunities.

Read More
Chat Window Trigger