Name: ______Block: ______Date: ______

IP 614

Catch a Wave Lab: Observe, Discuss, and Analyze

Purpose:

This lab is designed to explore different properties of waves in springs.

Prior Knowledge:

You need to follow directions that include the following vocabulary: amplitude, reflection, wavelength, medium, pulse

Materials:

Each group needs a meter stick, three people, a stopwatch, and a long spring (telephone cord)

Roles:

Two Spring Holders and One Recorder/Timer

When you return to the classroom, everyone in your group will work together to make sure that everyone fills in his or her lab sheet.

Observe:

General Procedure:

Get together with your partners and gather materials listed above.

Follow the directions in each section. Answer the questions in the space provided, using proper writing and clear diagrams.

Return to class when done.

Part A: General Motion Of A Pulse

  1. Have two people sit on the ground holding the long spring.
  2. Carefully– so as not to get it tangled or kinked – stretch it out on the floor.
  3. One of you should give the spring a rapid jerk by shaking it to one side then back so that you create a wave pulse that travels to the other end. Be sure your partner holds his end fixed.
  4. Repeat several times, observing what happens to the wave pulse as it travels to your partner and back.
  5. In what direction does the pulse move and in what direction does the spring move?

The pulse moves(Circle one)side to sideforward and backward.

The spring moves(Circle one)side to sideforward and backward.

  1. Do the pulse and the spring move in the same direction or perpendicular to each other?

The pulse and the spring move: (circle one) in the same direction

perpendicular to each other

  1. What happens to the amplitude of the pulse as it travels away from its source? (Circle one)

The amplitude stays the same size as the pulse travels away from its source.

The amplitude gets smaller as the pulse travels away from its source.

The amplitude gets larger as the pulse travels away from its source.

  1. What happens to the wavelength of the pulse as it travels to your partner? (Circle one)

The wavelength stays the same size as the pulse travels to your partner.

The wavelength gets smaller as the pulse travels to your partner.

The wavelength gets larger as the pulse travels to your partner.

Part B. When the Pulse Hits the End

  1. Stay seated on the floor. Make sure that there is some tension in the spring.
  2. Have one person make a pulse while the other person holds the spring as motionless as possible.
  3. The pictures at right represent what the wave looks like as it travels from left to right, approaching the person holding the spring motionless.
/
  1. There are three sets of pictures below. Choose which set is MOST LIKE what happens to your spring after the pulse reaches the end that is held motionless. Circle your choice.

Set A
/ Set B
/ Set C

Part C. A Relationship between Amplitude and Wave Speed:

  1. Does the size of the pulse (its amplitude, how wide you snap it) have anything to do with the speed? Make a hypothesis: ______
  2. Hold the two ends of the spring a distance apart such that you can get a good pulse going from one end to another.
  3. Measure the distance. How long is the spring? ______m
  4. If a wave makes a round trip from one end to the other and back again, how far has the wave traveled? ______m (This is the TOTAL DISTANCE.)
  5. Now practice making pulses with a big amplitude, a medium and a small.
  6. Then measure the round-trip time for a big pulse three times, medium three times, and small three times. Record these as you measure them.

Size of Pulse / Time #1 (s) / Time #2 (s) / Time #3 (s)
Big
Medium
Little

Part D. A Relationship between Tension and Wave Speed:

  1. Does the tension in the spring have anything to do with the speed of a wave? Make a hypothesis: ______
  2. Have two people sit on the ground holding the long spring. One person should make a pulse that goes to the other end and comes back. Move closer together and make another pulse. Repeat until you find the shortest distance over which you can observe the pulse traveling away and returning to its starting point.
  3. Measure this distance and record it on the line labeled "Short" for LENGTH.
  4. The timer should time how long it takes for the pulse to go all way to the other person and back. (The timing should stop when the person who made the pulse gets it back.) Do this a total of three times. Record your times in the chart below.
  5. Then stretch the spring to find the longest distance over which you can observe the pulse traveling out and coming back. BE CAREFUL!
  6. Measure the distance and record it on the line in the table labeled "Far" for LENGTH.
  7. Again, find the round trip time for the pulse three times.
  8. Now find a length about halfway between the other two lengths. Get similar data and record it in the row labeled "Medium."

Length (m) / Distance (m) / Time #1
(s) / Time #2
(s) / Time #3
(s)
Short
Medium
Far

Discuss

Important Definitions:

A wave is a ______that transfers ______from place to place.

A vibration is a wiggle in ______.

A wave is a wiggle in ______and ______.

The source of all waves is a ______.

A medium is a ______through which waves can travel.

A mechanical wave is a wave that transfers energy through ______. A mechanical wave requires a ______.

An electromagnetic wave is a wave that transfers energy through ______. An electromagnetic wave does not require a ______.

A transverse wave is a wave in which the particles of the medium move ______to the direction of the wave motion.

DEMONSTRATION: A different way of making a wave will be demonstrated. Describe how this differs from the wave you made in the lab.

______

______

A longitudinal wave is a wave in which the particles of the medium move ______to the direction of the wave motion.
Anatomy of a Transverse Wave:

Crests: ______and ______. Troughs: ______and ______

Amplitude: A measure of the amount of ______being transported.

  • Height from the dotted line to Point ______OR
  • height from the dotted line to Point ______OR
  • height from the dotted line to Point ______OR
  • height from the dotted line to Point ______.

Wavelength: Distance from Point A to Point ______OR

  • Distance from Point B to Point ______OR
  • Distance from Point C to Point ______OR
  • Distance from Point D to Point ______

Anatomy of a Longitudinal Wave

Compressions: The part of the medium where the particles are ______.

Rarefactions: The part of the medium where the particles are ______.

How fast is that wave going?

The period is the amount of ______is takes for one wave to pass. Period is measured in ______.

The frequency is the number of complete ______passing a point every second that passes. The unit for frequency is the Hertz.

The wavespeed is the ______a wave travels per unit time. Wavespeed is measured in meters per second.

There are two important relationships to know:

  • Period is the number of seconds per wave and frequency is the number of waves per second. Thus, period and frequency are inverses of each other.
  • The “wavespeed equation” This is how we MEASURE wavespeed.

We’ll practice using these two relationships later.

Outside factors that DO affect wavespeed:

  • THE MEDIUM!!!!
  • Tension, density, elasticity, temperature etc.

Factors that DO NOT affect wavespeed:

  • Amplitude, wavelength, frequency, etc.

Behaviors of Waves:

All waves can exhibit the following behaviors:

Reflection: to ______

Refraction: to ______

Transmission: to ______through

Absorption: to be ______up.

Interference: two or more waves ______through each other.

DEMONSTRATION: You will see a wave get to an end that is NOT held motionless. In what way is the result different from what happened before?

______

______

DEMONSTRATION: You will see a wave travel from one medium to another. Record your observations. ______

______

DEMONSTRATION: Destructive interference is difficult to notice. We will look at this together. Based upon these observations and discussions, what happens when to opposite-side pulses meet?

______

______

We’ll examine reflection, refraction, transmission and absorption in more depth as we study sound and light.

Interference:

  • Constructive Interference: When two waves add together to create a wave with a ______amplitude.
  • Destructive Interference: When two waves add together to create a wave with a ______amplitude.

Analyze

Part A: General Motion Of A Pulse

  1. List the names of the two types of waves.

______

______

  1. Use a complete sentence (or two) to describe the motion of a transverse wave. Be sure to include descriptions of what happens to the amplitude and the wavelength as the pulse travels.

______

______

______

______

  1. Thinking about energy, why does the amplitude of the wave pulse decrease as the pulse travels? Where does the energy go?

______

______

Part B. When the Pulse Hits the End

  1. Write general rules for what happens when a wave encounters a motionless end.

After reflecting, the pulse’s amplitude is now ______.

After reflecting, the pulse is located ______.

  1. Write general rules for what happens when a wave encounters a loose end.

After reflecting, the pulse’s amplitude is now ______.

After reflecting, the pulse is located ______.

  1. Write a general rule for what happens to a wave when it encounters a change in medium:

When a wave pulse encounters a boundary between two mediums, some of the wave pulse is ______and the rest is ______. Thus some energy is ______and some is ______.

Part C. A Relationship between Amplitude and Wave Speed:

  1. Copy your data from part D into the below table and then calculate the average times.
  2. Copy your total distance here: ______.
  3. Calculate the speed with which the pulse traveled. (Remember speed = total distance / average time)

Size of Pulse / Time #1 (s) / Time #2 (s) / Time #3 (s) / Average Time (s) / Speed (m/s)
Big
Medium
Little
  1. Does the amplitude affect the speed significantly? (Circle one) yes no

Part D. A Relationship between Tension and Wave Speed:

  1. Copy your data from part E into the below table and then calculate the average times for your three trials at each length. Also double your lengths to find your distances.
  2. Find the speed of the wave by dividing the total distance traveled by the average time.

Length (m) / Distance (m) / Time #1
(s) / Time #2
(s) / Time #3
(s) / Average Time (s) / Speed
(m/s)
Short
Medium
Far
  1. As you stretched the spring, its tension grew. How is the speed of the wave related to tension?
  2. When the spring has more tension, the pulse travels with a ______speed.
  3. When the spring has less tension, the pulse travels with a ______speed.