Blog 7: Circular Motion

Sunday night, 11:49pm.  I'm sitting at home, studying my physics notes as I do every night, when I suddenly realize we have a blog due. Panic mode commence.  I frantically search my humble abode for signs of circular motion.  None to be found.  I curl up I my bed, about ready to accept defeat, when suddenly a bikini hits me in the face.  I stare up angrily at my fan where I had hung my bikini earily today so it could dry.  So there I am, looking at the rotating fan blades, when I suddenly realize I am staring straight into the eyes of circular motion. I said a quick prayer to the physics gods for blessing me with the perfect example of cirular motion despite my procrastination as I took this video of my fan.  In this video I turned the speed of my fan up so that the other bikinis I was drying on my fan flew off as well.  Because it is on a high speed, it has higher centripetal accleration than it did when it was roatating slower because centripetal accleration = velocity squared / radius.  The radius of the fan is constant during every speed so as the velocity increase or decreases, so does the centripetal acceleration.  The centripetal force that was keeping the bikinis on the fan blades was friction.  Centripetal force is equal to (mass)(centripetal acceleration).  As the velocity increased, so did centripetal accleration untill  mac was greater than the centripetal force which was keeping the bikinis in circular motion.  The bikinis flew off in a path the was tangent to the circle.  Thanks to physics I know to keep my fan on a low speed so that I dont get hit with things flying off my fan when their centriptal acceleration becomes too great.

Blog 6: Collisions

This weekend my friends and I decided to have a friendly volleyball tournament.  I was super excited because even though I'm horrible at volleyball, I knew I'd see a lot of examples of momentum and collisions that I could blog about!  In this picture you can see the Bret (left) has hit the ball toward Sean (in the red) who is trying to block it.  The volleyball's momentum is equal to its mass times its velocity.  After Bret hit it, the ball then collided with Sean's hands and bounced back towards Bret.  A bouncy collision! The collision created an impulse which is equal to change in momtum or force times mass.  The ball experienced a large change in momentum so it its impulse must have been pretty big.  Because the time that the ball was in contact with Sean's hands was extremely short, that must mean the the force was very large (J=F  t ) .  Ouch, his hands must've hurt after this from all the force...

Blog 4: Energy, Work and Power

These are pictures of my friend Allie (top) and me (bottom) climbing trees.  The act of climbing a tree incorporates many physics concepts that we have learned about: energy, work and power.  Allie and I are gaining potential energy (mgh) as we climb the tree.  The higher we climb, the more potential energy we have because our h is greater. However, if when we both reached the platform and had the same height, I had more potential energy because my mass is greater.  This also means I did more work.  Work equals the change in energy and since our kinetic energy at the bottom and at the top is 0, then the change is kinetic energy = 0, so work can be calculate by the change in potential energy.  Since I ended up with more potential energy, I did more work.  I also climbed up the tree WAY faster than Allie, so I was also more poweful.  Power is calcuated by dividing work done by the time it takes to do the work.  Doing a lot of work in a short amount of time makes something very powerful.  Therefore because I did more work AND did it faster, I was definately more powerful than Allie.

Once we climbed up to the platform, we ziplined down.  We could calculate the speed at which we ziplined down by using the conservation on total energy.  Because out kinetic energy on the platform = 0 and out potential energy at the end of the zipline = 0, our potential energy (mgh) at the platform would equal our kinetic energy (1/2mv^2) at the bottom.  Solving for v would tell us how fast we were going.

Blog 3: Defying Newton's Laws

Today my mom asked me to burn her a CD of all the pictures I took on our trip this past summer. While I was doing this, I came across this picture I took of a man I saw on a street in Barcelona who was floating in mid air! At the time I was flabbergasted and wondered how it was physcially possible.  However, I have learned a lot since then and when I saw this today I thought, "Physics must have an answer!" I turned to Newton and his trusty laws to explain it.

Newton's first law of motion states that an object at rest stays at rest and an object in motion continues moving at a constant velocity unless acted upon by a net external force.  If this is true, the man should accelerate downards because the force of gravity is  acting on him.  However, he just floated there, motionless. 

Newton's second law states that Accleration = Net Force / Mass.  Because the acceleration of the man is zero, that must mean that the net force also is equal to zero. In order for net force to be zero,  there must be another force acting on the man that is equal in magnitude but opposite in direction of gravity to make Fnet = 0. So I guess he is pushing up on his stick with a force of 9.8 N?  But it still seems impossible. Maybe gravity just doesn't affect him. I wish Newton was here to see this...

Blog 2: Projectiles

This morning for breakfast I decided to open my new box of Honeynut Cheerios and surprisingly I found that not only does this healthy cereal help lower cholesterol, it also teaches you about physics! As I poured myself a bowl, out fell my very own "Penguin Launcher".  Intrigued as to what this little toy was, I turned the box around and to my delight I saw that the entire back of the cereal box was covered in diagrams relating to projectiles!  The toy is basically a plastic "penguin" that you place on the launcher which you then press down to fling the penguin both upwards and forwards at the same time.  When you launch the penguin you give it both an initial horizontal velocity and an initial vertical velocity.  Although the horizontal velocity is constant the entire time the penguin is in freefall, the vertical velocity accelerates at a rate of -9.8 m/s giving the flight of the penguin a parabolic shape.  While it is in the air it is only under the influence of gravity.  Without gravity, the parabolic shape would be impossible because the penguin would continue in a straight line path as both its horizontal velocity and vertical velocity stay constant. 

One one the sections on the back of the cereal box asked "Do you have enough projectile pop to push your Penguin over the top of the box?" Being a good physics student, I took the challenge and decided to see if I could launch my penguin over the box.  It took me a couple tries but I finally got the pengin to go oever the box.  The trick is to launch it really hard so it has an initial vertical velocity great enough to reach a height greater than the cereal box.  If I timed the amount of time it was in the air and how high the penguin went, I could calculate its inital vertical velocity using the equation y = (initial velocity)(time)+ 1/2 (vertical acceleration)(time squared). 

Notice the parabolic shape of the projectile motion!

Physics of Football

Yesterday I went to the Iolani Football at Aloha Stadium and witnessed a lot of good physics! This picture is from the Kamehameha vs. Saint Louis game and shows the Saint Louis kicker about to kick the extra point after the touchdown.  The ball starts at rest on the ground with an initial velocity of zero m/s.  As soon as the kicker kicks it, the ball is in freefall accelerating at a rate of -9.8 m/sq. seconds, the force of gravity.  The velocity decreased at a constant rate the entire time it is in freefall. The ball travels up for the same amount of time as it travels down because of the constant force of gravity.  The extra point kicks were just one example of the physics found at a football game.