A Practical Application of the Fundamentals of Physics.

 

Gravity, the force that attracts a body toward the center of the Earth, seems to be out to get me. I have been described as being “made out of fall down”. This is because I fall down. A lot. I have long legs and big feet and sometimes I don’t pick them up, so I trip. I ride my bike to work a lot and sometimes the potholes get me. Occasionally my adventures in science result in mystery bruises. Bruises and scrapes I can handle, but recently I had the opportunity to test some of Newton’s Laws in other ways.

physics1

I, in my little Dodge Caliber, was hit by a GMC pickup truck. After I took a hot minute to get my wits about me, I crawled out and looked at was left of the tail end of my car. My first thought? “Good job, crumple zones. Good job….” This is how we got to this blog entry. It’s been a while since High School Physics, so let’s all get caught up on some basics:

  • Inertia is the tendency of an object to resist any change in its velocity (speed+direction).
  • A fancier way to say that? Newton’s First Law of Motion states that a body at rest remains at rest unless acted upon by an external force and a body in motion continues to move at a constant speed in a straight line unless it is acted upon by an external force.
  • Force = Mass x Acceleration (if Acceleration is the rate of change of the velocity)

 

physics2

 

In other words, unless some outside force acts on an object it will keep on going or staying, as the case may be. One of those outside forces is friction. Which brings us to inertia. A bigger, heavier object will take longer to get to a high rate of speed, but if the same force is applied, it will also take a longer time to slow down too. So a ping pong ball takes a lot less effort to stop than a freight train, but it also takes a lot less effort to throw a ping pong ball than it does a freight train. And so that brings us to the practical application portion of today’s blog.

Specifically, in the case of my accident, my little car had almost come to a stop when I was hit from behind. Since the truck was so much bigger, the truck had more momentum than my car brakes could handle—so I was pushed forward, even though the truck slowed significantly.

physics3
Even though there was a lot of damage done to the rear end of my car, I was still safe. This is because some physicists and engineers (thank you!) have been working to make vehicles safer. To do this, they have to take into account Newton’s Laws of Motion. Some of the safety features cars have these days are seat belts, crumple zones, air bags and specialized tires. Since you can’t instantaneously change the mass of the vehicles in an accident, your best bet is to change the acceleration to reduce the force. The function of the seat belts, crumple zones and air bags is to do just that by slowing things down more gradually. They change the acceleration of the person inside the vehicle by increasing the time it takes for the accident to occur – even if it is just by fractions of seconds.

Seatbelts comprise about 50% of your protection in a car. When a driver stops the car suddenly, the driver tends to lunge forward, because the driver’s body tends to maintain its speed and direction. The seat belt holds the driver and prevents the driver from flying forwards when the car stops. Seat belts help by applying a force that overcomes your inertia as in Newton’s First Law. They also increase the time in the wreck which results in a lesser impact force on you; more time means less acceleration to you! Even when your body comes to a stop, however, your internal organs continue to move, slamming against each other because of the impact. So, that’s fun.

Good tires are also an important safety feature on your car. The friction between the tires and the road determines the maximum acceleration and the minimum stopping distance. If the surface of a tire is rougher, then the friction force is larger. This is super important if you are slamming on your brakes to avoid something or speeding up, also to avoid something.

physics4


Prior to 1959, people believed the more rigid the structure, the safer the car. This ended up being deadly because the force from the impact went straight to the passenger. Crumple zones are specially engineered areas on your car that are designed to absorb energy as they are crushed and slow down the rest of the car more gradually. They absorb energy from a collision and therefore reduce the force of a collision on the passengers. They aren’t just spots that are softer or less dense on the car, they are specifically engineered to crush in a relatively gradual and predictable way that absorbs much of the impact energy, keeping it away from the occupants in what is termed a “controlled crush”.

So! Buckle up and be safe, and good job, crumple zones…good job.

Sports Science: Olympics Edition ‒ Freestyle Swimming

Every four years, the eyes of the world shift towards a global competition, complete with feats of strength, determination, talent and teamwork. The Summer Olympics are back, and I could not be more excited. The following post is one of three about some of my favorite events.

As a college student, one of my pre-Finals rituals was to stop studying 30 minutes before leaving for the exam and instead watch sports highlights videos to get pumped up. There was Vince Young coasting into the corner of the endzone in the 2006 Rose Bowl, Tracy McGrady scoring 13 points in 35 seconds to knock off the Spurs, Landon Donovan sending the U.S. to the knockout stages of the 2010 World Cup, and, the grand finale, the 2008 Men’s 4x100m freestyle relay, the race that earned Michael Phelps his second of eight gold medals at the Beijing Olympics.

That race was, to me, the most memorable moment of a historic run for Phelps. Set aside the volcanic eruption of American pride for a second, and just consider the physics at play as anchor leg Jason Lezak breaks French hearts and sends his teammates into delirium.

Mickey Kelly Swims

Freestyle swimming in and of itself is a case study in aerodynamic motion. The swimmer’s body must be in as straight a line as possible while moving through the water to reduce drag. The swimmer’s face needs to be down as much as possible to allow the round waterproof cap the opportunity to part the water most efficiently. Even when the swimmer turns his head to breathe, the horizontal line should be maintained and the deviation in motion should be minimized.

The body should be in a constant state of motion, and all motion should be synchronized as much as possible, with kicks matching the strokes of the arms. Deviations from this synchronization will cause drag. In addition, small, quick kicks are generally more effective than large kicks that require more time; essentially, the sum of many short accelerations is greater than one large acceleration.

So going back to Lezak’s final 50 meters in the relay, it is important to first set the scene: Lezak was trailing the world-record holder in the 100-meter freestyle, France’s Alain Bernard, by about 0.5 seconds heading into the last leg of the race. That lead had expanded to 0.6 seconds after the first 50 meters.

Lezak closed the gap, in part, due to a principle of physics common in racing of all kinds: drafting. The concept here is you get as close as you can to the racer in front of you; that racer absorbs the brunt of the drag, leaving a pocket of “clean” air (or water). The racer behind the leader uses less energy to go the same speed or can use the same energy to gain ground.

Note how Lezak is swimming at the top of his lane, as close as he could possibly be to Bernard’s slipstream. Even though he is not directly behind Bernard, his positioning is actually much more similar to the way that birds fly in a V-shape while migrating. The ideal position for this technique is at around the waist of the other swimmer, which you might notice is just where Lezak is at about the halfway point of the last length of the race. The disturbance that Bernard is causing in the water radiates outwards and creates a small pocket of clean water for Lezak to cut through.

Studies have shown that swimmers in open water races using slipstreams to swim consume about 10% less oxygen than others and reduce the rate of perceived exertion by 21%. And while it’s a technique that annoys people in the neighborhood pool, it’s something that helped Lezak make up a half-body length deficit in 25 meters and win the race by 0.08 seconds. Oh yeah, there’s also that Olympics Gold Medal.

Swimming events at the Rio Games begin Aug. 6 and conclude Aug. 13.

The Science of Summer

Why does ice cream look different when it melts in your car and gets refrozen?
If you have ever made homemade ice cream, you may have noticed that it takes a lot of work. My family’s ice cream maker looked a lot like this one which was electric but needed a little more monitoring than the ones we have today.

Ice_Cream_Maker_Rival_Electronic_8605-M

The key to some good ice cream is keeping it at the perfect temperature and keeping it moving. Commercial creameries have special machines that continually stirs the ice cream while it is being frozen. These machines cool the ice cream much more quickly than my home machine ever could, which is why their ice cream is much creamier. It prevents larger ice crystals from freezing in the ice cream.

When ice cream melts in the Houston heat on your way home from the grocery store, you may notice that it’s not quite the same consistency any more. If you put the ice cream back into the freezer, it will refreeze, but over a longer period of time than the original ice cream. In addition when you re-freeze the ice cream, you aren’t churning the mixture. This allows larger crystals to form which affects its appearance and its creamy consistency. It is not recommended to refreeze ice cream that has been left out for a longer period of time. Ice cream is made out of dairy, so it can grow bacteria or spoil if left out for too long!

10-Essential-Facts-About-Sunscreen-722x406
How does sunscreen actually work?
First, we have to talk about what happens to cause your skin to burn. When you are out in the sun, your skin is exposed to sunlight which is made from ultraviolet (UV) radiation. Ultraviolet radiation can be subdivided into three categories based on wavelength. UV-A radiation has the longest wavelength. It is not absorbed by our atmosphere’s ozone layer and it is the type of UV that is responsible for long term skin damage. UV-B radiation has a shorter wavelength than UV-A. Some of the UV-B radiation is absorbed by the ozone layer and the remaining UV-B radiation that reaches the earth’s surface is responsible for sunburns. The last type of UV radiation is UV-C radiation. It has the shortest wavelength and it is completely absorbed by our atmosphere. On the Earth’s surface, we are not affected by UV-C radiation, but it could be an issue for astronauts if they didn’t have those protective suits. Sunscreen protects our skin from the two most common forms of UV radiation on the earth’s surface – UV-A and UV-B.

Essentially, sunscreen forms a thin, invisible protective layer on the surface of our skin. It uses organic and inorganic active ingredients to form that protective layer. The organic ingredients such as octyl methoxycinnamate and oxybenzone absorb UV rays. When the rays are absorbed, the energy is harmlessly dissipated in the form of heat. Some of the organic materials in sunscreen will slowly break down over time, which is why we need to reapply sunscreen regularly. The inorganic active ingredients like zinc oxide or titanium dioxide reflect the UV radiation essentially preventing the UV radiation from hitting the skin. Early versions of sunscreen were opaque and white, which reflected the UV radiation well. However, it wasn’t the most appealing look for the beach. With newer technology, they’ve made these inorganic materials much smaller and nearly invisible.

255718_stock-photo-three-melting-ice-cubes

How can I cool down a warm beverage quickly?
It’s the middle of summer, and when you walk outside it feels like you have walked through a curtain of heat and humidity. Nothing sounds better in a Houston summer than a nice, cold drink. But we’ve all forgotten to move something from the pantry to the fridge, and ended up with a warm drink instead. Even when you move that drink to the fridge, it can take over 45 minutes to reach the cool temperature you’d prefer. Here are a few ways to cool down your beverage quickly, and the science on how it works.

Option 1: The Wet Paper Towel Method.
Wrap your bottle or can in a wet paper towel and place in the fridge. The drink will cool down much faster with the wet paper towel because of how heat is transferred. Normally, heat will transfer from a higher temperature object to a lower temperature object. In the case of the drink in the fridge, the heat will transfer from the soda can (higher temperature) to the air in the fridge (lower temperature). Heat can be more easily transferred through a solid like the soda can because the atoms are closer together on average. It is much more difficult with a gas like the air in the fridge because the atoms are more spread out on average. When we put a wet paper towel onto the outside of the can, we are using a liquid to facilitate the transfer of heat more easily than with air. Water from the towel will evaporate from the towel and the remaining water will be cooler. This process is called evaporative cooling. The wet towel also conducts the heat from the can cooling the soda to the temperature you prefer.

Option 2: The Salt & Ice Water Method.
Fill a bowl with ice and water, then pour salt over the icy mixture. Place the can or bottle in the bowl, and stir. It should be colder in about 5 minutes. The reason that this method works so well is trifold. First, you are lowering the melting point of the ice when you add salt so the mixture will be colder than 32° F. Basically as the ice is melting, it is using up a little bit of energy to break bonds causing the remaining water to be colder. Having a colder liquid helps the heat transfer between the liquid and the soda can. Which brings me to the second reason that it cools quickly – it’s a liquid! As we mentioned in option 1, heat can be transferred more easily through water than through air, so the water is facilitating the heat transfer. Lastly, stirring the bottle or can around in the mixture can reduce the amount of time needed to cool down the soda. If you did not stir the mixture, then the can would slowly transfer heat to the liquid surrounding it making the liquid immediately surrounding it warmer. The transfer of heat would continue slowly until both the can and the liquid reach equilibrium. By stirring the mixture, you are exposing the can to more of the cold water which speeds up the transfer of heat. In both situations, the can and liquid are reaching equilibrium, but over different amounts of time.

With either cooling option, you will get a nice cold beverage quickly and now you know the science behind it!

Have Science Fun in the Summer Sun with a Solar Print Kit!

by Marina Torres

Texas heat is here, and school’s out for summer. With all that bright sun outside, it’s a great time to play under the open sky. In the spirit of the season, we took science outside with a do-it-yourself kit from our own Museum Store. This super fun and educational solar print kit really leaves an impression! With this kit, you can challenge your children’s imagination and keep them active.

kit

Here’s what it comes with:12 five-by-seven pieces of solar paper, two print frame holders, two pre-printed stencil sheets and three blank note cards with envelopes so kids can share their finished projects with friends and families.

kit2

And here’s how it works: First, lay everything out.

Cut out the pre-printed stencil images and gather the items you’d like to use in your image. In a dim room, place the solar sheet (located inside the black envelope) under the frame, with the blue side facing up. Place the items on top of the sheet and close the frame.

kit3

Carefully place the system under the bright summer sun for about three minutes or until the sheet turns white.

kit4

Gather your items and prints out of the sun, then rinse under running water and let them dry.

kit6

Voila! You’ve merged art and science into one, and created these super cool solar images!

kit7

Visit the Museum Store or shop online for this solar print kit and other DIY kits or browse around for other summer toys. We’ve also opened an exciting new Cabinet of Curiosities section inspired by our newest exhibition. There’s never been a better time to start your own collection!

Editor’s Note: Marina is the Visual Manager for the Houston Museum of Natural Science Museum Store.