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Archive for the ‘Physics’ Category

The Physics of Free Running

Posted by drdavescience on May 21, 2008

Good news everyone, I am officially Dr. Dave! I spent the past few months writing my Ph.D. thesis, and I successfully defended my dissertation. I apologize for not posting regularly, but I am sure you understand.

Thesis Break, Bond Style!

While I was writing my thesis, I would occasionally take a break and watch a movie. One of the movies I watched was Casino Royale, the most recent entry in the Bond franchise.

Chase scenes are standard in Bond movies and Casino Royale had its fair share. My favorite is when Bond pursues a bomb maker, Mollaka, on foot through a construction site in Madagascar.

Below is a link to the scene posted on YouTube. The clip is about 9 minutes long.

In this foot chase, Bond and Mollaka have two different styles. Mollaka is graceful and efficient; Bond is aggressive and haphazard. It is clear that Mollaka has an advantage over Mr. Bond.

Free Running

Sébastien Foucan, the founder of a sport called free running, played Mollaka. Free running is a sport that is dedicated to efficient motion between two points.

During the foot chase, Mollaka knew how to use his environment to keep him moving forward. While his jumps were very fancy to watch, he was clearly using the laws of physics to his advantage.

Rolling, Rolling, Rolling

Free running reminds me of martial arts. I have several friends who perform similar acrobatic feats during martial arts demonstrations. The core philosophy of many martial arts is to redirect energy, and I imagine the same holds true for free running.

A basic move taught in many martial arts is rolling. A proper roll is a useful move that is designed to dissipate energy in a fall or jump.

Look at this YouTube video showing how rolls are done. The people in this video clearly know what they are doing. Please don’t try this at home without the proper equipment. You can easily injure yourself.

The examples toward the end of the video show why the roll is a great move–it helps the free runner maintain his forward momentum after a jump and places him on his feet.

The Physics of Going Splat

In the YouTube examples above, we can see how rolling is very useful to free runners. Let’s learn about the physics of this motion.

Let’s imagine we have a ball of pizza dough. What happens if you throw it against the wall? I would predict that it would go splat and flatten. Why?

When the dough collides with the wall all the energy of motion–called kinetic energy– is instantly absorbed by the pizza dough. Let’s think about what happen in another example.

Now imagine that we roll the ball of dough on the ground towards a wall. What happens in this case? The ball of dough will gradually lose speed before hitting the wall. In this example, the dough is more likely to maintain its shape because the energy is lost gradually as it rolls rather than suddenly at impact.

In both cases, a similar amount of energy is lost. What matters most is the amount of time required for the dough to slow down. If it the dough stops suddenly, then it will flatten. If the dough slows gradually, it will retain its original shape.

Over the Handlebars

While pizza dough is a good example, let’s think about how this works on a human body. The following is a true story.

A friend of mine was riding his bike in the park. Suddenly, a child jumped in front of him, causing my friend to swerve and avoid the child. Unfortunately my friend hit a bench and went flying over the handlebars.

Being a black belt martial artist, he instinctively curled up into a ball and rolled on the pavement; he rolled a few times before coming to a complete stop.

The Physics of Not Going Splat

My friend was able to avoid significant injury because was able to roll and gradually dissipate his kinetic energy. Imagine what would have happened if he landed hard onto the pavement. His body would have suddenly impacted the ground and instantly absorbed all kinetic energy. If you have ever experienced a crash, then you know this is a painful experience.

In the example of pizza dough mentioned above, a direct impact caused the dough to lose its shape. On the human body, a sudden impact would cause significant injury, like cuts and bruises, even broken bones. Ouch!

Whether you are a martial artist or a free runner, the ability to move with proper technique helps to prevent injury. By understanding physics we now know why. Remember, it all boils down to how fast or slow kinetic energy is dissipated.

–Dr. Dave

Posted in Fun Facts!, Physics, Sports | Leave a Comment »

Pitching Ace and Physics Master

Posted by drdavescience on March 12, 2008

Physics is concerned with how things move, energy, space, and time. In an everyday sense physics explains how planes fly, how electricity flows from an electrical outlet to a light bulb, and even how glasses help people to see better.

Perhaps one of the coolest everyday example of physics is in sports. Since spring is around the corner, I will focus on baseball.

I think pitchers are masters of physics. They know how to throw a ball with great speed and precision so that it will land in the strike zone.

Let’s take a closer look at the pitching process.

During the wind-up, a pitcher uses his body to transfer energy to the ball. This energy is called kinetic energy, the energy of motion.

As the baseball is being released, pitchers sometimes add some spin. This can cause the ball to take a curving path, rather than straight path, which can confuse the batter.

Breaking it Down

We know from experience that if we hold a ball and simply let it go, gravity will pull it down.

We also know that when we throw the ball straight ahead, the ball will fly forward while arcing downwards. If you think about it, there are two things the affect how the ball flies, the throw and gravity.

Now, if you throw the ball, but this time you release it with a spin, the ball will fly forward, arc downwards, and curve in the direction of the spin. In this case the throw, gravity, and the spin affects how the ball flies.

The best way to understand this concept is with a few good examples. A friend suggested this impressive wiffleball pitching video because it clearly illustrates the effect of spin on pitching. Keep your eyes on the ball!

The pitchers in this video are able to get such amazing curveballs because the plastic wiffleball is very light and more easily affected by spin than a heavier baseball.

When baseball season starts-up, do not forget to root for your favorite physics master, I mean pitcher!

-Dr. Dave

Posted in Physics, Sports | Leave a Comment »

Indiana Jones and the Mystery of the Cracking Whip

Posted by drdavescience on March 3, 2008

Indiana Jones and the Raiders of the Lost Ark is my favorite movie. I was watching it (again), and a friend asked me why a whip makes that characteristic “crack” sound. As a reminder, below is a YouTube video montage of Indiana Jones’ favorite weapon.

Where does the sound come from?

When you move something through the air really fast, it typically makes a “whoosh” kind of sound. If you swing a bat very fast, you can hear this sound. This is just the air moving around the bat. Cars and planes also make their own “whoosh” kind of sound, but no “crack” sound.

The distinctive whip “crack” sound occurs when the tip of the whip is moving at supersonic speeds.

This means that the tip of the whip is breaking the sound barrier! Isn’t that cool!

A similar sound is made when a fighter jet breaks the sound barrier. Check out this You Tube video of a fighter jet breaking the sound barrier.

I mentioned that only the tip of the whip moves at supersonic speed. As Indiana swings and snaps the whip, all of the energy of motion moves down to the tip and causes it to changes directions rapidly. When done properly, it cracks.

-Dr. Dave

Posted in Check it out!, Fun Facts!, How does it work?, Physics | Leave a Comment »

Heavy Metal Glider

Posted by drdavescience on January 27, 2008

In mid-January, a British Airways 777 landing at London’s Heathrow Airport crash-landed short of the runway. When the jet was 600 feet above the ground (about 2 miles from the runway) the engines stopped responding – it effectively became a big glider.

Most jets fly at about 150 mph during the landing phase. In the scenario I described above, the pilots had less than 30 seconds identify the problem (the engines had stopped responding), have the cabin crew prepare the plane for an emergency and glide it towards the runway. The plane touched down short of the runway and sustained major damage, but the most important thing is that nobody was seriously injured. The landing had more to it than just luck, and the pilots and the crew did a great job,

Gliding and Training

Some people seem to think that when the airplane’s engines stop, the plane will drop out of the sky. It is not well known is that all airplanes are designed to glide. In fact, big jets are very efficient gliders; with a lot of altitude, a big jet can glide far. I’ll talk about a few examples later in this article.

Pilots are trained to handle all sorts of emergencies when they first learn how to fly. In fact, during my own private pilot training, my flight instructors taught me how to handle engine failures. This was the most nerve-wracking emergency to practice because I had one chance to land safely.

Notable Airliner-Gliders

In 2001 a Air Transat flight 236 was flying from Toronto, Canada to Lisbon, Portugal. Somewhere across the Atlantic, the engines failed due to fuel starvation (the pilots did not notice there was a slow fuel leak due to a faulty part). Starting at about 30,000 feet, the pilots managed to glide the airplane for about 20 minutes to a safe landing in the Azores. Impressive!

In 1982, a British Airways 747 flew into volcanic ash and all four engines failed. The plane was at 37,000 feet and it was able to glide down to about 13,000 feet (about 12 minutes) before the crew restarted 3 of the engines and landed safely.

The Glide Ratio

All airplanes come with a manual that is full of charts that help pilots predict an airplane’s performance during take-off, cruise, and landing. There is also a section that indicates the airplane’s glide ratio. A glide ratio indicates how many miles the airplane will glide over a given altitude loss. For example, the small plane I fly, a Diamond Star, has glide ratio of 1.4 miles per 1000 feet of altitude lost.

A 747 has a glide ratio of about 2.8 miles per 1000 feet of altitude lost at its best glide speed. This means that a 747 cruising at around 35,000 feet can glide almost 100 miles if it loses engine power!

Modern airplanes are very reliable. Several thousand aircraft are flying everyday without incident, which is a testament to the high standards of pilot training and maintenance.

Keep up the good work!

-Dr. Dave

Posted in How does it work?, In the News, Physics | Leave a Comment »

Heat Transfer in the Kitchen

Posted by drdavescience on December 26, 2007

Merry Christmas! I apologize for the lack of posts. Things are very hectic because I am finishing my Ph.D. and looking for jobs. Both tasks are very time consuming.

I would like to thank people who read my posts and send nice comments. I am glad to know that my ideas and explanations are having an impact in people’s understanding. Your kind notes inspire me to write more posts.

Happy 2008 to everyone!

-Dr. Dave

—–

In honor of Remy, the culinary genius from the recent Disney/Pixar movie Ratatouille, I will discuss the science behind cooking.

Cooking is one of my favorite forms of science because in the end, you can eat your experiment.

A great chef is both a scientist and an artist. They constantly experiment with different combinations of flavors and foods to create fantastic tasting meals. Do you remember the last time you had a really great pizza, or had a fantastic desert that knocked your socks off? What made it taste so good?

The science of heat

Cooking is the transfer of heat energy from some source to the food. In the kitchen there are three devices that are used to cook food: the stovetop, conventional oven, and microwave oven. Each of theses devices are designed around a different method of heat transfer.

The movement of heat is so important that there is a name for it: Thermodynamics. By understanding how heat moves, we can gain insight into our everyday world. It is responsible for the weather, car engines, your refrigerator, cooking, and a host of other things that you may not have even thought about.

Heat is transferred in three basic ways listed below:

Conduction is heat transfer through direct contact. When cooking on the stovetop, the heat from the flame or electric grill is applied directly to the frying pan. This means that only the flat surface of the pan is sufficiently hot enough to cook anything and we must flip and toss around the food to cook it properly.

It is important to note that most pans are made of metals, like copper, that conduct heat very efficiently and do not melt on the stovetop.

Convection is heat transfer through a fluid. The fluid can be liquid or gas and in the case of a convection oven, the fluid we care about is air.

A convection oven is a confined area that gets hot by flames or electric coils. The air inside is warmed to a desired temperature and, as a result, cooks the food from all directions. This method of heat transfer is responsible for pizzas, cakes, and other baked treats!

Keep in mind that convection ovens heat foods from the outside. The inside slowly heats up with time, and it is not uncommon to see food where the outside looks done, but the inside is uncooked. This is very important when preparing a Thanksgiving turkey, and there are special thermometers that measure the temperature of the food in the center of the turkey to show that it is properly cooked.

Radiation is the transfer of heat using electromagnetic radiation. A microwave oven uses very strong radio waves (a form of electromagnetic radiation), which are very weak and not hot. So how does it work?

Microwave ovens work by spinning water, fats, sugars and oils inside the food. This causes friction, which then heats the food and cooks it from the inside.

Please do not be confused by the word radiation or electromagnetic radiation. In science, these terms are very general and mean a lot of things. Radiation comes from many sources, some are beneficial and others are harmful. For example, solar radiation from the Sun is responsible for heating the Earth and the light we see is a form of electromagnetic radiation.

As you know, heat is very important in the cooking process. Now you have the basic knowledge of heat transfer.

Look at the world around you. Don’t be afraid to ask, “How does that work?” Be curious and seek help from people willing to help you (like me).

Let your curiosity guide you through this everyday world.

-Dr. Dave

Posted in Cooking, How does it work?, Physics | Leave a Comment »

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Archive for the ‘Physics’ Category

The Physics of Free Running

Pitching Ace and Physics Master

Indiana Jones and the Mystery of the Cracking Whip

Heavy Metal Glider

Heat Transfer in the Kitchen