Blog 6-Car collision

On Friday I got my permit (FINALLY!).  As dorky as it is, I spent my Thanksgiving night reading and studying the driver's manual.  During the section "Safe Driving Techniques," the book discusses the necessity of wearing seat belts.  There was a nifty little diagram which showed a time lapse sequence of a car hitting a brick wall.  This reminded me of the various physics concepts used to design safety precautions in the event of a car crash.

First, I was reminded of the design of a car.  The hood is long and made of aluminum so that in a crash it crumples, increasing the time of the collision and thereby decreasing the force exerted on the car.  This design uses the concept of conservation of momentum and the equation: momentum=force x time, or p=Ft.  While in the diagram there is no comparison to the design of the car, we know from our own experiments in the lab that a faster time will have a greater force exerted on the car.  However, the diagram does compare the difference of wearing a seat belt.

Seat belts are designed based on the law of inertia.  A person's body will continue to move forward even though the car has stopped during a crash.  Simply put, seat belts strap a person down to his or her seat so that he or she does not fly through the front windshield.  The bottom left drawing in the diagram shows the person without a seat belt beginning to fly through the windshield because he or she is still moving at 30 miles per hour.  However, the bottom right drawing shows the person safely strapped in because he or she is wearing a seat belt.

Therefore, safety during a car crash uses many physics principles in order to design better safety precautions.  

The image used above was taken from page 62 of The Hawaii Driver's Manual.

Blog 5-Ziptrek

This summer my family spent a few days in Whistler.  Since it was the summer, there wasn't enough snow to ski/snowboard, so we did other outdoorsy things.  One of the things we did was the Ziptrek, which is an ecotour where a person gets strapped to a set of cables that sort of interlace and cross over Fitzsimmons Creek.  You get a ton of amazing views on it. I don't know how to describe it, so this is the link explaining more about it: http://www.ziptrek.com.

The really cool thing about this trek, besides it being super eco-friendly, is that it is based entirely on physics concepts.  The wires are attached to the trees at downward sloping angles.  The rest is left up to gravity.  However, you have to be of a certain mass so that you don't get stuck in the middle.  This pretty much just uses basic kinematic equations.

At the end of the cable, the guides set up a hook and then "reel" each person in.  The concepts involving momentum were used to create this system.  The hook is set up a certain distance away and increases the time and distance that a person  travels while slowing down after flying over the creek, thereby decreasing the force exerted on the person.  The hook system makes stopping much more comfortable for the person on the Zipline.

The picture above is my dad stopping on the Zipline.  I think Matt will like it.

Blog 4-Class Day

At class day, my group of friends and I took a picture in or surrounding a tree.  I was perched the farthest out on the tallest tree branch that we were either on or around.  

The other two people on my branch were Mark and Shireen. Mark is approximately 67 kg and was about 1.4 meters off the ground so his potential energy was 919.24 J.  Shireen is approximately 45.5 kg and was about 1.55 so her potential energy was about 691.15 J.  I am about 50 kg and about 1.7 meters off the ground so my potential energy was about 833 J.  

The only problem with this situation is that out of the three I was probably the least agile/athletically talented.  After the picture was taken, I was sort of stuck in the tree like a cat.  It was really sad.

However, I was able to get off of the tree by standing and then sitting on Mark's shoulders.  By getting onto his shoulders, I lowered my potential energy to about 490 J.

Of course, he thought it would be funny if he started spinning while I was still sitting on his shoulders.  The spinning added kinetic energy to the system (I don't know his velocity so I cannot calculate the kinetic or total energy).  

This picture is after Mark stopped spinning.  As you can see, I was crouching and didn't really want to be there.

While all of this energy was going on, our awesome chaperone lay happily in the warm sun, absorbing another sort of energy :)  

Blog 3: Inertia

As I rode in the car this weekend, I saw how inertia affects our everyday lives.  Traffic is a great example of Newton's first law due to the constant yet sudden starting and stopping.  As the car from a stop accelerates to 20 miles per hour, my body at first leaned back because it wanted to stay at rest.  However, I eventually gained speed and moved along with the rest of the car at 20 miles per hour.  When the car came to a sudden stop, my body wanted to continue moving at 20 miles per hour, the speed I had been traveling at, so I flew forward.  The seat belts stopped my body from continuing to move forward.  This prevented me from going through the front windshield of the car.  Therefore, due to physics and Newton's first law, seat belts are necessary when riding in a car.

After we got home, we reenacted this situation on an empty side street.  I used a phone to make this video so the quality is kinda bad.  Also, sorry for my language at the end.  It's not anything too bad :)

Blog 2: Straws

Today I ate breakfast/lunch at Zippy's.  While eating, Kevin took my straw, which still had the wrapping on it, and shot the wrapper at me.  Later on, as I was eating at my extremely slow pace, I decided to play around with the straw and wrapper.  I stuck the wrapper back on the straw and blew on the straw.  Of course, with my good luck, the straw flew across the restaurant into some random booth.  I hid underneath the table to avoid being caught, but I don't think the people noticed.

As always, there IS physics (and a point) in my lengthy and unimportant stories.  The wrapper of the straw was the projectile in this example.  It flew (kinda) in a parabolic motion.  The initial velocity of the wrapper depends on how hard someone blew on the straw.  The harder a person blows on a straw, the faster and farther the wrapper will fly.  The horizontal velocity of the wrapper remains constant, while the vertical velocity changes due to gravity’s pull (-9.8 m/s^2).  The graphs of the straw would resemble #4 on this weekend's homework (but obviously different labels).  However, air resistance affected the straw wrapper’s path since the projectile is so small and lightweight.

The pictures are at my house because I didn't have a camera at the restaurant.  It also avoided other incidents like my straw-blowing attempt.  In the first one, the projectile is at its initial velocity as it flies off the straw.  The second frame shows the wrapper in flight.  The shutter speed of the camera isn't very quick, so the projectile is slightly blurry.

Blog 1-Reaction time

I was stuck at home the whole weekend since I was sick, SOOOO I ended up playing with my dogs quite often.  When I got really bored I tossed each of them a kibble.  My dogs are pretty old (10 and 13 years old), so they aren't very well coordinated.  

However, I got to see the difference in their reaction times.  I think I kinda proved that dogs take after their owners, because I have a pretty slow reaction time, and so do my dogs.  I accidentally hit my smaller dog in the head a couple of times because her reaction time was so slow! XD

There were several physics concepts at work in this example.  The velocity and distance that the kibble traveled differed.  Often times, when my dogs were farther away, they would catch the kibble.  However, when they were closer, they had less time to react, and they either missed the kibble or got hit by it.  Also, the speed at which I tossed the kibble affected their reaction time.  If I threw it quickly when they weren't looking, they usually missed the kibble.  However, if I threw it lightly and they were looking at me, they caught it (most of the ti

me).

The image at the top shows the speed of one of my dog's reaction.  She sees the kibble coming at her, yet she did not open her mouth quickly enough to catch it.  (This one hit her in the head.)

The picture at the bottom is my smarter yet older dog.  He knew that it would be easier for him to catch the kibble if he sat farther away.

No animals were harmed in the making of this blog.