What are waves?
A wave is a disturbance that moves energy from one place to another.
The material a wave travels through, like water or air, only moves back and forth; it doesn’t travel with the wave.
How Waves Are Formed
Waves are created by a disturbance in a medium. A disturbance is just a shake or movement that provides energy.
The medium is the material the wave travels through, like a rope, a spring, or water.
The disturbance makes the medium’s particles move, which then pass the energy to their neighbors, creating a wave that travels outward. The medium itself does not travel with the wave.
Here are three ways to create waves, as discussed in the text:
Using a Rope: Creating Waves with a Rope
How to Make Waves: To create waves, we need two things:
- Attach one end of a rope firmly to a wall
- Hold the other end and move it up and down repeatedly
What Happens: When you move your end of the rope up and down, you create a pattern called oscillations or vibrations. These movements travel along the rope toward the wall like ripples moving across water.
Important Observation: Here’s the key point that might seem surprising at first:
- The waves move horizontally along the rope (from your hand toward the wall)
- But the rope itself only moves vertically (up and down)
- The rope doesn’t actually travel anywhere – it stays in the same place while the wave pattern moves through it
Understanding the Medium: The rope serves as the “medium” – this means it’s the material that carries the wave from one place to another. Think of it like a messenger that passes along information without leaving its post.
Using a Slinky Spring
A slinky spring is a pre-compressed helical (spiral-shaped) or coiled spring. Think of it as a metal spring that has been wound up into tight coils, as shown in the diagrams.
Laboratory Experiments with a Slinky
We can perform several experiments in the laboratory using a slinky to better understand how wave motion works.
Basic Setup
Step 1: Preparation
- Attach one end of the slinky spring firmly to a wall
- This creates a fixed point that won’t move
Step 2: Positioning
- Place the slinky horizontally on a table
- Hold the free end in your hand
Experiment 1: Horizontal Movement
What to do:
- Move the free end of the slinky left and right continuously
- Keep the movements horizontal (sideways)
What you’ll observe:
- The coils of the spring will move left and right
- Wave patterns (humps) will travel from your hand toward the wall (the fixed end)
- You can clearly see these humps moving along the spring
Experiment 2: Back and Forth Movement
What to do:
- Move the free end of the slinky back and forth horizontally
- Push toward the wall, then pull away from it, repeatedly
What you’ll observe:
These compressed regions travel from the free end toward the fixed end at the wall
Individual coils move forward and backward
Some areas become compressed (coils squeezed together)
Using a Ripple Tank
What is a Ripple Tank?
A ripple tank is a special piece of laboratory equipment designed to study waves. It consists of:
- A shallow glass tank filled with water
- A light source positioned above the tank
- The light shines down through the water to make wave patterns visible on a screen below
How Does a Ripple Tank Work?
The Setup:
- The tank is illuminated from above so light passes through the water
- This lighting system helps us clearly see the wave patterns as they form and move
- The waves cast shadows that make them easy to observe and study
Creating Water Waves:
- A small vibrator (like a motor with an attached rod) moves up and down
- This vibrator touches the water surface repeatedly
- Each time it touches the water, it creates a disturbance
What Happens When Waves Form?
The Process:
- The vibrator moves up and down, touching the water surface
- This creates water particles at the surface that also move up and down
- These moving particles cause nearby water particles to move up and down too
- This up and down motion spreads across the entire water surface
- The result is a pattern of ripples moving outward from the vibrator
Key Observation:
- The water itself doesn’t travel across the tank
- Instead, the wave energy moves through the water
- Individual water particles move up and down, but the wave pattern moves outward
- The water acts as the “medium” – the material that carries the wave energy