How UH scored the 1st 2 points...Physics Incompetence!

Yesterday, I went to watch the UH vs. Boise State football game. Not that I'm a huge UH football fan or someone who actually understands the game of football, but I did witness some awesome physics in action! So for people who didn't watch the game, UH finally scored the 1st 2 points in the 3rd quarter due to a safety or something (still not completely sure what that means). Anyways, the Boise State center snapped the ball to their quarterback, but because the angle of the initial velocity with the ground was too high, the ball flew over the quarterback's head. Next, a UH player tried to catch the ball, but because his hands were held out stiffly, the time of impact with the ball and his hands was reduced. Therefore, the force needed to stop the ball increased because of the impulse=F*elapsed time equation. The increase in force needed to stop the ball caused the ball to bounce out of the UH player's stiff hands. Since the UH player couldn't catch the ball, he tackled the Boise State player, and UH got 2 points for the safety! (Sorry if this is inaccurate because I don't completely understand the game of football...)

The Last 100m Sprint (supposedly)-XC

This is a picture of me approaching the finish line at the Kamehameha Invitational last Saturday. After learning about momentum and impulse this week, I realized that these concepts closely tie into the finish of a cross-country race. My understanding of momentum and impulse from physics has helped me to understand why my coach tells everyone to run THROUGH the finish line (as opposed to stopping at the finish line). Impulse is equal to the change in momentum and the average force*elapsed time. Momentum is mass*velocity, so the change in my momentum at the finish is equal to -my mass*my sprinting speed because if I stop completely at the end my final velocity is 0. The value for change in momentum should be equal to average force*elapsed time, since both expressions are equivalent to impulse. Because the change in momentum is not 0, the equation requires that the elapsed time cannot be zero either. Therefore, since I am changing my momentum at the finish line, I must take time to slow down to rest; I cannot stop instantaneously. Because I have to slow down over a period of time to make the change in momentum, I would have to start decreasing my speed before the finish line in order to stop at the finish line. This would mean that I cannot run at sprinting speed for the whole 100m stretch, hence a slower time and getting passed by other runners right at the finish line. By following the coach's advice and running THROUGH the finish line, I will start reducing my speed after I cross the finish line, so I will be able to run the entire last 100m at top speed (and hopefully pass other runners who aren't thinking about the physics behind their race finish).

Physics Toy

I came across this toy and totally thought of the wonderful world of Physics! When you push down one of the dolphins and then let go, the dolphins on each side move towards the ball in a circular path alternatively. First of all, because of the low friction between the metal parts, the dolphins will continue to move for quite some time after one of the dolphins was first pushed down. This exhibits Newton's first law of motion because the dolphins continue to move until the force of friction eventually acts on the system. This dolphin toy also shows the idea of conservation of total mechanical energy. When one pair of dolphins is pulled up a certain distance and held at rest, the kinetic energy is 0 and the potential energy is mgh. The total mechanical energy of the pair of dolphins just before they change direction is the same as the total mechanical energy in the beginning, except in the end the potential energy is 0 and the kinetic energy is mgh. The forces acting on the system include a magnetic force from a magnet inside the blue base (pulling the dolphin downwards), gravity (which is always, always, always pulling down towards the center of the earth, and tension.

A Shower of Projectile Motion

I decided to take a break and shower after many hours of studying. Even though I tried to avoid thinking, a few physics concepts hit me on the head (quite literally actually). I realized that the stream of water coming out from the shower head exhibited projectile motion. Since the direction of the initial horizontal velocity was parallel to the ground and there was no initial vertical velocity, the equations in the picture represent the distance from the shower head to the ground and the horizontal distance from the shower head in which the stream of water lands. Since we learned in the projectile labs (the ones with the monkeys and bananas) that vertical and horizontal motion are independent, I know that when I adjusted the strength of the water stream, I was only changing the initial horizontal velocity (and therefore the horizontal displacement), not the time it takes for the stream of water to travel from the shower head to the ground. It's amazing how physics is everywhere in the world around us. We can never escape the laws of physics!