Monday, September 20, 2010

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!

Monday, September 6, 2010

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.