Magnetic Thinking Putty is infused with millions of micron-sized (one-millionth of a meter) magnetic particles. These particles are what give Magnetic Thinking Putty its strange attraction properties.
Last week, the TED-Ed Animation Team facilitated animation workshops with TED-Ed Innovative Educators. We introduced them to basic stop-motion tricks and techniques in hopes that they would begin to incorporate animation into their classroom projects - and based on the results, I think they are up to the challenge!
Earlier this fall, we sourced some fun facts from the educators themselves, and then tasked them with visualizing that very information. We used tablets with #istopmotion to shoot the animation, and basic household objects and school supplies as props and materials. We dare say that you, too, can do this from home!
1. When an object’s mass doubles, its kinetic energy also doubles, but when an object’s SPEED doubles, its kinetic energy quadruples.
2. If a male sperm was the size of a human being, it would swim the 100 metre freestyle in half of the world record time.
3. Approximately one word is added to the English language every two hours.
4. If you condensed the Earth’s history into 24 hours, humans wouldn’t exist until 11:58pm.
The way radar guns work to find out the speed of an object is that a high frequency radio wave is transmitted from the gun onto the object whose speed you would like to measure.
This wave bounces off the moving object and then returns back to the radar gun.
A circuit in the gun amplifies the signals and adds them together.
Case – I
Let’s consider a stationary object. Any wave that hits the object reflects back and get back to you in the same frequency.
Since the frequency of the received wave is same as the transmitted wave, you get another wave with the same frequency when you add them up.
Case – II
Now if that object is moving with some velocity, your reflected wave would be “Doppler shifted”.
Doppler effect is the increase (or decrease) in the frequency of sound, light, or other waves as the source and observer move toward (or away from) each other.
This means the frequency of the received wave is different than the transmitted wave. And when you add those two signals of different frequencies up you get a pulsating beats effect:
Since each velocity corresponds to a particular beat frequency, radar guns use the beat frequency as a measure to find out how fast an object is moving.
For example, if 60mph corresponds to a 20 Hz beat frequency.
If you are moving at 100mph instead (say), the beat frequency measured by a cop’s radar gun would be higher than 20Hz.
And that’s how cops know exactly how fast you were going! Have a great day! Drive safe!
** This post masks a huge chunk of engineering of that goes behind making one of these for the sake of simplicity.
But if you would like to learn more about the circuit underlying radar guns, an useful starting point would be this video
Since water is diamagnetic(they are slightly repelled by magnetic fields ) when one brings a strong Neodymium magnet near its surface, it makes a slight dent on it.
In this video this is visualized by placing a striped pattern as the background. Without a magnet, the water surface is calm and the striped pattern appears as is.
But when a magnetic field is introduced, the water surface is no longer flat and changes the way the light gets reflected off it.
Have a good one!
* An analogy:
If you have had a dent on your car, then you might be able to relate to this phenomenon. Before the dent, the surface was smooth and the car looked great, but after the dent light reflecting off it just makes the dent look more prominent.
In our case we are making a forcibly making a dent in order to prove that the water is diamagnetic using a powerful magnet. The light reflecting off it just makes this dent look prominent.
In this set of images the smoke from an incense stick is seen making a transition from a smooth laminar flow (very close to the incense stick) to a turbulent flow (far away from the incense stick) while passing through the Kelvin-Helmholtz instability (rolling vortices).
** This post is part of the ‘Flow series’ by FYPhysics and EcstasyShots!. Check out the previous posts here.
When you wake up in the morning and open/close your faucet when you brush your teeth, you might have noticed that it undergoes a transition between a smooth jet to a dripping flow like so :
When the velocity of the fluid exiting the faucet is high, it appears smooth for a longer time before it breaks into droplets:
But when you make the velocity of the fluid exiting the faucet low, it seems to form droplets much earlier than before.
Here’s the water breaking into smaller droplets shot in slow motion:
Notice that just by changing the exit velocity of the water you can control when the droplets form.
You can also control the nature of the droplets that form by changing fluids. Here’s how it looks like if you use water as the fluid (left), pure glycerol(center) and a polymeric fluid(right).
A simple answer to this is perturbations on the surface of the fluid. What does that mean?
Initially the fluid is just falling under the influence of gravity. And velocity of any freely falling object increases as it falls:
But the surface tension of the fluid holds the molecules of the fluid together as they fall down.
Therefore depending on the initial velocity of fluid, the surface tension of the fluid and the acceleration you get a characteristic shape of the jet as it falls down:
This is what you observe as the fluid exits the faucet.
Perturbations
Just after exiting the faucet, there are tiny perturbations on the surface of this fluid as it falls down. This is apparent when you record the flow at 3000fps:
Those tiny perturbations on the surface of the fluid grow as the fluid falls down i.e the jet becomes unstable.
And as a result the fluid jet breaks down to smaller droplets to reach a more thermodynamically favorable state. This is known as the Plateau-Rayleigh instability.
It takes different fluids different time scales to reach this instability. This depends on the velocity of the fluid, the surface tension and the acceleration it experiences.
And some viscous fluids like honey are also able to dampen out these perturbations that occur on their surface enabling them to remain as fluid thread for an extended time.
A note on inkjet printers
By externally perturbing the fluid instead of making the fluid do its own thing, you can make droplets of specific sizes and shapes.
This engineerguy video explains how this is used in inkjet printers in grand detail. Do check it out.
We started today by trying to understand why water exiting a faucet behaves the way it does. Hopefully this blog post has gotten you a step closer to realizing that. Have a great day!
Sources and more:
* This is a topic that is home to a lot of research work and interesting fluid dynamics. If you like to explore more take a look into the mathematical treatment of this instability here.
** This post is part of the ‘Flow series’ by FYPhysics and EcstasyShots!. Check out the previous posts here.
I hand you an object and ask you to predict whether the object would float or sink. How would you go about doing that ?
Well, you can measure the mass of the object and the volume of the object and can derive this quantity called Average Density
It is the average density of the entire object as a whole. If this object is submerged in a fluid of density , then we can draw the following force diagram:
Fun Experiment:
If you drop some raisins in soda, you will notice that they raise up and fall down like so (Try it out!):
This is because air bubbles that form on the top of the raisin decrease its average density to the point that its able to make the raisin raise all the way from the bottom to the top.
BUT once it reaches the top all the air bubbles escape into the atmosphere (its average density increases) and the raisin now falls down.
Questions to ponder:
Why do people not sink in the dead sea ?
How are submarines/divers able to move up and down the ocean ? How would you extend the average density argument in this case.
Why do air bubbles in soda always want to raise up ?
If the total load that needs to on a ship is 25 tons. What should be the total volume of the ship in order to remain afloat if the density of sea water is 1029 kg/m3,
** This post is part of the ‘Flow series’ by FYPhysics and EcstasyShots!. Check out the previous posts here.
One of the most surprising things about air that may not be intuitive is that it is a fluid and like any other fluids exerts a pressure on objects.
Standing on earth with layers of air above us, we are constantly being ‘weighed down’ by a pressure of ~1atm at all times.
All objects in air are also assisted by a buoyant force that is caused from the pressure difference between the top and bottom surfaces.
Let’s now consider the hot-air balloon in particular. A force diagram is probably the best way to start:
Therefore we see that in order for the hot air balloon to float, we need to have the buoyant force compensate for the net weight from the balloon, the load on it and the air inside it:
And with a spectacular burner onboard our hot air balloon, we can easily increase the temperature of the air inside the balloon!
That’s pretty much how hot-air balloons work! You increase the temperature of the air inside the balloon to go up, decrease the temperature to go down and skillfully adjust the temperature to hover.
Have a great day!
Questions to ponder:
When you increase the temperature of air, its density decreases. What do you think happens to all the molecules that were previously inside ? Do they exit the balloon ?
Different shaped hot-air balloons is a common sight. Do you think that the Buoyant force changes for each shape?
Recently we stumbled upon this cheap high voltage converter on Amazon which claims a boost from 3-6V to 400kV.
Although really skeptical about the 400kV claim, a lot of comments indicated that it did boost at the very least to 10kV so we got one of these to test it out.
Schematic diagram for lighting up a CFL using the high voltage converter
Using a 1.5V battery to power the circuit
Using a 3V battery to power the circuit
And boom! There we go, that’s how you light up a CFL light bulb using a 3V battery!
If you do have access to a plasma globe or a tesla coil, things become a little bit more simpler:
Wireless (but not free) means to power a CFL light bulb
The way CFL light bulbs works is by exciting the electrons in the lamp and when they return to the ground state they radiate ultraviolet light. This emitted light is converted to visible light when it strikes the fluorescent coating on the glass.
So it really does not matter how you decide to excite the electrons to the higher energy state. It might be a high voltage converter, a tesla coil, a plasma globe, etc but all you need is a device that will kick those electrons inside the bulb from their ground state to the higher excite state. That’s all you need!
When you search for videos online of plucking a string on an instrument such as the guitar, a surprising number of searches lead you to videos such as the following:
This is not how plucked strings look like! This also does not have anything to do with harmonics of the instrument as well.
The reason why you are seeing those shapes on the guitar is due to the rolling shutter effect on your camera.
But if you do want to see how plucked strings look like, the following videos would be your best bet:
In the first post of our fluid mechanics series : ‘Flow’ we explore the concept of Buoyancy. Click here to check out the post exploring the physics of Buoyancy.
Have a great day!
* Check out the video description on YouTube on the details of how buoyancy is related to each clip in the video
Premiering in the summer of 2019 is a web series that we have been working on titled ‘Flow’ which is aimed at expressing the beauty of Fluids through the looking glass of a slow motion camera.
Here is a trailer to the upcoming series. Hope you guys enjoy it!
These images were captured from an airplane overlooking San Fransisco. But there’s something interesting going on here and something you can try the next time you are flying.
Right near the the middle of the image you should be able to notice a haze in the image. This is due to the exhaust from the engine.
Hot air is less dense than cold air.
And this creates a gradient in the refractive index of the air.
The turbulence of the air emanating from the exhaust gases also has a direct correlation to the degree of distortion of the image.
More the turbulence, more the distortion.
Although the above image is from a commercial aircraft, the effect is even more dramatic in fighter jets.
Have a great day!
* The term that is used to describe this phenomenon is ‘Heat Haze’. You can read more about this here.
This week NASA released the first-ever image of shock waves interacting between two supersonic aircraft. It’s a stunning effort, requiring a cutting-edge version of a century-old photographic technique and perfect coordination between three airplanes – the two supersonic Air Force T-38s and the NASA B-200 King Air that captured the image. The T-38s are flying in formation, roughly 30 ft apart, and the interaction of their shock waves is distinctly visible. The otherwise straight lines curve sharply near their intersections.
Fully capturing this kind of behavior in ground-based tests or in computer simulation is incredibly difficult, and engineers will no doubt be studying and comparing every one of these images with those smaller-scale counterparts. NASA developed this system as part of their ongoing project for commercial supersonic technologies. (Image credit: NASA Armstrong; submitted by multiple readers)
How do these images get captured?
It may not obvious as to how this image was generated because if you have heard about Schlieren imaging what you have in your head is a setup that looks something like:
But how does Schelerin photography scale up to capturing moving objects in the sky?
Heat Haze
When viewing objects through the exhaust gases emanating from the nozzle of aircrafts, one can observe the image to be distorted.
Hot air is less dense than cold air.
And this creates a gradient in the refractive index of the air
Light gets bent/distorted
Method-01 : BOSCO ( Background-Oriented Schlieren using Celestial Objects )
You make the aircraft whose shock-wave that you would like to analyze pass across the sun in the sky.
You place a hydrogen alpha filter on your ground based telescope and observe this:
Notice the ripples that pass through the sunspots
The different air density caused by the aircraft bends the specific wavelength of light from the sun. This allows us to see the density gradient like the case of our heat wave above.
We can now calculate how far each “speckle” on the sun moved, and that gives us the following Schlieren image.
**** This post obviously oversimplifies the technique. A lot of research goes into the processing of these images. But the motive of the post was to give you an idea of the method used to capture the image, the underlying science goes much deeper than this post.
What about those with power prescriptions you ask ?
These days you can find a lot of people even with power prescriptions sporting glasses/lenses that turn dark when exposed to sunlight. These are known as Photochromic lenses.
Let’s do a quick demo:
This is a photochromic lens getting exposed to 395-400 nm light turning dark as a result.
To learn how this is achieved it must be understood that there are these class of reactions called ‘Reversible reactions’
A and B can react to form C and D or, in the reverse reaction, C and D can react to form A and B.
Example of reversible reaction of Bismuth Chloride
In the case of Bismuth Chloride, sunlight acts as a mediator to change it from a transparent solution to a dark colored solution and shaking in air brings it back.
In the case of Photochromic lenses, an organic dye is used that darkens under UV and lightens under its absence
If you ever have had the unfortunate experience of leaving your plastic in the sun or wondered why the colors of your clothes fade away, then the technical term to express your misery is Photo-degradation.
This is the other extreme of a reversible reaction where UV light from the sun break break down the chemical bonds in the plastic and clothes (called chromophores) and eventually leads to fading of the colors in the object
The catch
As any user of one of these Photochromic lenses will tell you, there are some aspects of these lenses that still need to be improved
- The chemical reaction rate depends on the temperature of the surrounding. This means that on a sunny day if you are in a really warm climate, the lenses will adapt faster than if you live in a cold climate
- Most car windshields block UV light to some extent and therefore these lenses are not effective when you are inside the car.
- They do degrade after a while. Most of lenses do degrade having been used after a couple of years and need to be changed.
But having said that Photochromic lens are indeed a really cool piece of technology.
