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Posts Tagged ‘Force’

On Friday, I worked the late malasada (Iolani Class of 2009!) shift from 8:15 to about 11 at night. I got to do quite a variety of things from selling malasadas in the front to squeezing the little balls of dough in the kitchen to washing the extremely oily pans. It was rather busy and I’m sure that entropy was increasing steadily under that white tent.

Anyways, I witnessed a plethora of physics at the fair on Friday. First, over half of the games involved projectile motion when aiming object A at/over/into/onto object B. So if you were equipped with your lovely kinematic equations, an invisible ruler, and a robotic arm, the games should have been child’s play.

And nearly all of the rides involved spinning about an axis and centripetal forces that point radially inward of magnitude mv^2/r. Unfortunately, they don’t go nearly fast enough. We should really have roller coasters instead. ūüėÄ

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Stress and Force

Seeing that I’ve have a throbbing headache for all of Sunday, this journal entry is rather late…Most likely this is all from an overload of stress. It’s very different from the physics sense of stress which I’m sure you all remember as amount of force exerted per unit area. Review time!

For much of this weekend, I’ve also been walking around at a constantish velocity carrying a VERY heavy box filled with tons and tons of pages. It was indeed very strenuous but according to physics, I wasn’t actually doing any work since the force applied and the distance the box moved were perpendicular to each other. That, however, didn’t stop me from getting an extremely sore back. Oh joy.

My Lovely Trophies!

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Elevator Physics

Ghostly Elevator!

My physics experience of the week was the hackneyed up and down an elevator one.  I ride the elevator in my apartment building everyday but this particular day was special.  My grandfather, on an around the world trip, arrived in Hawaii as his last stop and came to our place.  

As we went up the elevator this time, I had the sudden impulse (not in the physics sense) to explain the present physics of the situation.  From a position of rest, the elevator accelerated upwards.  Since Fnet=ma and the normal force was much larger than weight (mg), I felt heavy and bogged down.  During the long elevator ride, I explained the concept to my family members in Chinglish (an exotic mixture of Mandarin Chinese & English) since my grandfather can’t understand my English when I’m supposedly talking too fast.  It felt very good to be breaking through a language barrier!  My experience wasn’t so clichéd after all!  ^ ^ 

An hour later, on the way down, the net force was now downwards.¬† I explained how that since weight was now greater than the normal force, we felt much lighter.¬†¬†I think that my parents and grandfather really understood what I was saying‚Ķeither that or they were just oohing and nodding to humor me. ¬†On the other hand, my brother completely ignored me and started jumping up and down which made the elevator feel shaky.¬† Afterwards, he would also throw a projectile motion french fry at me by “pure accident”…twice…aren’t siblings just bundles of joy?

The next day, my grandfather went back to Shanghai.¬† Hopefully, he’ll spread the word about the wonders of physics!¬† He promised me he would at least try and act as my ambassador…since there’s an elevator in his apartment building too.¬† He also gave me 1,000 rmb.¬† Maybe I could use the money and start a ‘physics of an elevator’ awareness program!¬† : )

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Work, Physics, & Soccer

Yay for the long weekend!  Not so yay for the increased homework load and excessive number of tests next week!

On Saturday I got pathetically lost.¬† No need to get into details but I still blame a certain police officer and his completely¬†erroneous instructions.¬† Combined with my horrible sense of direction, it was…just bad.¬† Very bad.

So I basically end up circling a 500-acre park.  The only good things I got out of this two miles long detour were beautiful observations of the physics universe.  After all, it was hard to ignore the bajillions of tiny soccer players screaming and running.  And of course, the kicking of the muddy soccer ball.  (I did not have a camera at that moment, so here are substitute pictures.)

Beanie Soccer BallBeanie Soccer Ball 2Beanie Soccer Ball 3

One soccer ball had no kinetic energy, but not for long.¬† A youngster soon ran up to it and kicked it hard towards the goal.¬† The force exerted by¬†her foot accelerated the ball.¬† Expressed in a simple work-kinetic theorem equation, the work done by¬†her foot on the ball¬†should have been¬†equal to the change of kinetic energy of the ball.¬† However, to be more accurate, we’d have to account for friction between the ground and the soccer ball slowing it down too.

And did I mention that during this whole time, I was carrying my ponderous violin case with me? But since the force I was exerting (up) was perpendicular to the displacement (forward), a physicist would have concluded that I was not actually doing any work.  How sad.

Thankfully, the rest of Saturday was rather uneventful.¬† I did pretty much nothing except go¬†and check out Punahou’s “canteen” for the Class of 2013.¬† Lots and lots of food…and no one even noticed me. : )

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Physics of Rain

Knowledge I’ve gained after spending Friday and Saturday learning about policy debate and Sub-Saharan Africa: “The Malaria epidemic is like loading up seven Boeing 747 airliners each day, then deliberately crashing them into Mt. Kilimanjaro.”¬† : (¬† How can such a statistic not be depressing?

As¬†for physics…it started pouring on my way home on Saturday.¬† (Which was actually quite a liberating experience.)¬†

Let’s take the hypothetical average raindrop to be a few millimeters in diameter.¬† With only gravity, the drop would accelerate towards the Earth at 9.8 m/s¬≤.¬† That’s pretty scary considering that it falls from thousands of feet above sea level.¬† Luckily for us, there’s air resistance, an upward force which opposes motion in air.¬† Drag will increase as the velocity of the raindrop increases.¬† When that force is equal to the downward force of gravity, the raindrop reaches its maximum or terminal velocity.¬† Since a raindrop is so small, it reaches its terminal velocity rather quickly and therefore won’t cause too much physical harm to those out in the rain.

Furthermore, we could even calculate the change in potential energy as rain (it’s probably too difficult to find the mass in kg of a single droplet) falls to the ground with the handy equation below!¬†

őĒPE = mgőĒh

But we would expect the actual kinetic energy released from rainfall to be a much smaller number due to the opposing drag force. 

Anyways, throughout this whole experience I kept remembering the famous question, “Do you get wetter from walking or running in the rain?”¬† I’m sure the answer is physics-related…¬†maybe Doc could answer this. : )

Rain.jpg Rain picture by xtaintedwatersx

FYI: In the time it’s taken you to read this post, 4 more children have died from malaria.¬†

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