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 :)