Intro to Waves Lab

For this experiment, we used a spring and a stopwatch.

We started out with the spring stretched around six meters.

Part 1:

For this part, I placed my left hand about 50 centimeters up the spring while my right hand held the end back.  I then pulled my left hand back until it was close to my right, and let go. 

1) Describe in words and drawings what you see after releasing the spring.

It's hard to describe the motion in the spring, since it is unlike anything that occurs in everyday life.  It was if a current, that started from my left hand pulling back the loaded spring, traveled down to my partner's end of the spring, and then came right back.  The way I could tell a current was traveling was by the change in color that traveled down the spring (the change in color came from the loss of light when the spring cords touched).  

2) What happened to the wave when it reached the other end of the spring?

It was if the wave or current bounced off the other end and came right back towards me.  After the "bounce," the wave slowed down, but remained at a constant speed until it hit my end of the spring.  So the wave travels the same speed down the spring, until it hits the end, where it loses velocity.  The wave seemed to disappear after bouncing off my end.

Part 2:

For this part, while my right hand held the end of the spring, my left hand held the spring about 50 centimeters down.  I quickly moved that hand sharply out to the right about 30 centimeters and brought it right back.

3) Describe in words and drawings what you see after releasing the spring.

It looked like a wave, just like part 1, but this time it was much more visible.  This was due to the fact that the wave moved down the spring while that part of the spring stayed out to the right all the way down.  You can picture it by imaging an egg traveling down a snake's neck.  You can see the outline of the egg stretching the skin.  So that first sharp turn of the spring at the beginning traveled down to the end.

4) Describe in words and drawings what happens to the waves when it reaches the other end of the spring.

When the wave hit the other end of the spring, the egg-looking part of the spring changed sides, so now the outward current that was traveling towards me was on the other side than before.  The moving wave was smaller too; it didn't go out the full 30 centimeters.  Each time the wave hit an end, it would switch sides and shrink a bit.  The wave kept going until it's second time hitting my side, where it seemed to disappear.

5) Does the size of the wave change as it travels along the spring?  Describe both its amplitude and its wavelength.

As the wave traveled down the spring, the wavelength remained constant.  However, whenever it hit an end, the wavelength would slow a bit.  So a change in wavelength only occurred after hitting an end.  The amplitude also didn't change until after hitting an end.  The amplitude returned to equilibrium after hitting my side for the second time.

Part 3:

For this part, we did the same procedure as part 2, but used a stopwatch to see how long it took for the wave to return to my end of the spring.

6) How long did it take for the wave pulse to traveled from one end to the other and back?

I did three trials.  They came to be 1.75, 1.74, and 1.78 seconds.  So the pulse was traveling at around 6.85 m/s.

7) Do you think changing the amplitude of the wave will change its velocity?  Try it.

A change in amplitude ended up having no effect on the velocity.  If I pulled the spring out 50 cm instead of 30 cm, or 20 cm instead of 30, the time to return to my end of the spring was almost the same every time.

8) Do you think changing the wavelength will change its velocity? Try it.

The wavelength is represented by how fast the pulse travels down the spring.  We experimented by varying the speed in which I pulled out the spring to the side.  This also had no effect on the time it took for the pulse to return to my end.

9) Do you think stretching or shortening the length of the spring will change its velocity?  Try it.

This did have an effect on the velocity.  When we shortened the length of the spring to about four meters, we found the speed by doing distance/time or (m/s).  Since the wave had to travel down and back, the distance was eight meters.  The time it took for the wave to return to me took around 1.6 seconds after three trials.  So (8m/1.6s) = 5 m/s.  If you look up at part 6), the speed for six meters was about 1.75 m/s.  We found the speed through the same process when the spring was stretched nine meters, and the speed came out to be 9.5 m/s.  As you can see, lengthening the spring increases the velocity.  This is due to increasing tension in the spring.