Tag Archives: Waves

Pendulum Waves

You’ve already seen the way a no-flinch pendulum works, so now we are changing it up. This contraption is host to many pendulums next to each other but not touching. When you raise them up and let them go all at once, you can see something truly mesmerizing.

pendulum wave

They will all start to fall at the same rate, thanks to the laws of gravity, but after the first swing the will not be synchronized. This is due to them being uncoupled, or not connected, and to the length of each individual pendulum. The pendulum furthest away has the shortest length and the closest pendulum has the longest. All of the pendulums in the middle gradually become longer as they get closer.

The period of a pendulum is mostly dependent on its length. Since the lengths gradually increase, so will the periods, causing them to become out of sync. However, that can cause some pretty visually pleasing effects!

pendulum wave middle

Of course, given enough time, all of our pendulums will eventually line back up again in the end. But not before going through some other awesome patterns, as well as what may look like chaos.

pendulum wave end

This is not the easiest DIY project, but it is possible to recreate, so give it a try. Or you can always find it online or in store, but either way it is definitely worth seeing in person. Let us know what you think!

Written By: Mimi Garai

More Slinky Science

You can use slinkies to demonstrate all things waves! Start with the basics: wavelength, amplitude and frequency. Once you’ve got those down, then you can play around with some things that are a bit more complicated like wave type, standing waves, and superposition.

Longitudinal waves, like sound waves, expand and compress as they travel through a medium like air or water. Transverse waves are like ocean waves.  They have characteristics that we more commonly associate to a wave: wavelength, the distance from peak to peak or trough to trough, amplitude, the height of the wave, and frequency, the number of waves per given time.

As you increase the frequency of waves, you can also increase the number of nodes and antinodes in the standing wave. Nodes are the part of a standing wave that stay in place.  Antinodes are the part of a standing wave that move with maximum amplitude, like the peaks and troughs.  There is always one more node than antinode.

You can also cause superposition of waves.  Superposition is when you combine multiple waves together to get either constructive or destructive interference.  To get constructive interference, the waves must be in phase.  When call that coherent. Coherent light can often be found in lasers.  The light waves travel at the same frequency and are in phase, which results in a single point of light.  To get destructive interference, the waves would need to be sent out of phase, or be incoherent.  Light from a white flashlight is a great example of incoherence, because the light has many different frequencies, resulting in a cone shape of light.

In the case of the slinky. If you send one wave down to try to knock the water bottle over, on their own they do not carry enough energy. But, if both ends of the slinky are sent in phase and work together, then we can achieve constructive interference to knock the water bottle down!

What other waves can you think of, and is there a good way to demonstrate them?

DIY Wave Machine

Waves are everywhere! Electromagnetic waves traverse the vacuum of space. Gravitational waves ripple spacetime itself. Mechanical waves propagate energy through air, water, and other media.

Sound is a great example of a mechanical wave. Vibrating molecules disturb their neighbors, which disturb their neighbors, and so on. The individual units don’t move far, but the energy they transfer spreads widely. When the molecules closest to your ear jiggle back and forth, you perceive sound.

Soundwave2

Propagation of a sound wave in air. Image credit: HyperPhysics/Georgia State University

It’s easy to make your own mechanical wave machine at home. Center wooden skewers at approximately equal intervals (an inch or two apart works well) along a length of wide tape. Lay another strip of tape across the top of the skewers to hold them in place. Tension the system by attaching the ends of the tape to secure holding points. You’re ready to make waves! Lift and drop a single skewer end to generate a pulse. What happens?

Oscillate one skewer, and its neighbors move, too. The domino effect continues down the line even as the skewers themselves stay in their taped positions. Matter isn’t propagated along the machine, but energy is!

WaveMachineGif

For slower waves & easier observation, add mass to the ends of the skewers. We used modeling clay to weigh down each point.

Written By: Caela Barry

Soap in the Microwave Experiment

Woah! What just happened? To try and understand it, lets take a closer look at the Microwave. These are often thought of as magic food reheating boxes, but they are actually quite interesting!

Microwave ovens heat food by bombarding it with electromagnetic radiation, also known as light. Unlike the light most of us think of when we use that word, microwave light is invisible. All light travels in the form of waves, and these particular waves are stretched out too much for the human eye to detect.

EM Wave

This animation shows how an electomagnetic wave travels. It is actually two interconnecting waves, one electric and one magnetic. Source Dr. Hans Fuchs, Georg-August-Universität Göttingen

Eyes are great for detecting light, but they can only detect certain wavelengths of it. Most light is actually outside the realm of the human eye! Scientists often build telescopes to look at these other kinds of light like ultraviolet, x-ray, infrared, and even microwaves to see what it is that we are missing when looking at the sky with just our eyes.

EM_spectrum_compare_level1_lg

Different types of light make up the electromagnetic spectrum and are separated by their wavelength. The visible spectrum makes up a tiny portion of it. Image from NASA

Microwaves are also the perfect length for transferring heat energy to food. As the electromagnetic waves move through it, they bend the polar molecules (molecules that have positively charged and negatively charged ends)! As the molecules wiggle in microwaves, they bump into one another and speed each other up. Temperature is really just a way to measure how fast the molecules in something are moving, so as the molecules wiggle faster and faster, the food heats up! Just as importantly, they also heat up any pockets of gas that are trapped inside of whatever we’re trying to warm.

Ivory soap contains a huge number of microscopic air bubbles. When the microwave oven begins heating, two important things happen: the soap itself softens and melts, and the air trapped inside the soap expand.

Soap Expand

This is due to Charles’s Law, discussed here. Ultimately, the tiny air pockets in the Ivory soap grow into a giant froth of bubbles. You may have seen this process before… it’s the same science that causes popcorn to morph from small, dense kernels into fluffy, bite-sized chunks!

giphy

Popcorn kernel popping. Source 9gag.

So, have we fundamentally changed the soap? Not much! We’ve just made it take up more space. If you try this experiment at home, you’ll find that the solid suds still work. Be sure to let your creation cool for a few minutes before you touch it.

soappoke

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