torque and punching bags

This weekend, i was with my brother when he was working out hitting the punching bag. When he was hitting the bag i noticed that the bag swung more or less depending on the place he hit the bag. This reminded me of the torque equation that we learned on friday which is torque equals force times lever arm. The force that my brother was hitting the bag at is about the same no mater where he hits the bag. But the lower he hit the bad the further it traveled. this is because the axis of rotation is above the bad where the chain is mounted to the ceiling. The lower he hits the bad the longer the lever arm is. A longer lever arm with the same force increase the amount of torque. The net force of the torque translates into angular acceleration of the bag making it rotate up. The lower he hit the bag the more torque and the greater amount of angular acceleration. Another thing i noticed is that he always hit the bag perpendicular to the lever arm. This maximizes torque because only a compenet of the force applied transfers into torque. If he were dumb and hit the bag at the hinge, the will be no torque and angular acceleration because the lever arm is zero. If he were to hit the bag directly underneath and straight up toward the hinge he there will also be no torque and angular acceleration because there is no component of force perpendicular to the lever arm.

physics of fetch

This weekend i was playing fetch with my dog chewy and i realized that the two toys that i was throwing had to very different behaviors. The first toy i threw was stuffed animal. When i threw this toy it would fly through the air in a projectile like path and hit the ground and slide to a stop. The second object i threw was a tennis ball which also traveled in a projectile like path but it hit the grown and changed velocities in a bouncy collision several times before rolling to the rest. Both of these objects have about the same mass and were thrown at around the same velocity and same trajectory however, the tennis ball had a larger impulse. This is because the tennis ball had a greater change in velocity due to the bouncy than the stuffed animal did that had no vertical velocity after it hit the ground. I also noticed that the coeficeint of friction between the stuffed animal and the floor was greater than the tennis ball rolling on the floor because the ball traveled further after it stopped bouncing.

Energy of a Football Kickoff

This Friday i was at the Iolani homecoming Football game against Word of Life. While i was sitting in the hot son watching Andrew Skalman set the football on the kickoff tee i realized what he is about to do is what we are talking about in physics this week. The law of conservation of energy states that energy is conserved, so ignoring air resistance the sum of the PE and KE before the ball is kicked should be equal to the sum of PE and KE throughout the flight of the ball. However, when the ball is resting on the tee the ball has no KE because its velocity is zero and very low PE with respect to the ground. At the peak of the ball flight, the ball has very high PE with respect to the ground and a high KE because the ball is traveling foward. So how did the ball get the energy to accomplish it's flight. The answer is work is being done to the system by Andrew Skalman when he kicks the ball. The work he inputs (work=F x delta X) is equal to the sum of PE and KE (TE) at any point after the ball is kicked minus the KE and PE (TE) before the ball is kicked (ignoring air resistance). This proves that the law of conservation of energy holds true even if the sum of KE and PE are not equal at different points of the ball's path because work is being done.

Quarter 1

So far this has been my funnest class and the one i look froward to the most every day (other than free periods of course). I like this course because of the concepts make sense and when you understand you can understand how and why things act the way they do. My only anxiety is trying to keep up with my classes while trying to apply to colleges and deal with other stresses. Also trying to keep up with everything during the demands of the highschool soccer season. My goal is to the best i can in the class and learn the important concepts that i will use in an engineering major in college. So far i have been putting a good deal of effort into this class. I just have to make sure i do not start slacking off and getting lazy in the future. My performance has been pretty good so far. My tests are good but i gotta do better on my homework and my quizzes could be better to. Overall i'm doing well in this class because i enjoy physics.

Newton's second law

This weekend, me and my brother went running after a workout. Newton's second law states acceleration equals to Net Force divided by mass. Both of us are about equally as strong so our Net Force when running will be about the same but the difference is in our mass. My brother weighs about 30 more pounds than me so he has more mass. Newton's law states that the more mass an object has the more inertia it has. when my brother and I were running 40 yard sprints we were starting at a speed of zero and a net force of zero. At the start, we both had about the same net force when accelerating to our top speed but because my brother had more mass it takes more force to change his momentum because he has more tendency to stay in whatever motion hes in due to inertia. I was quicker to the 40 yard line because i had more acceleration. However, we also ran a mile after and the results were different. I was a little faster at the start because i had faster acceleration but my brother was able to keep up with me easily because the weight difference only affects our acceleration.

ping-pong projectile

This weekend I was at my friends house and playing a game of ping pong. Justin was my opponent and he beat me by a lot because he's a ping pong pro, but during the match i noticed that the ball traveled as a projectile. A projectile is an object that is traveling through the air with only gravity acting upon it. This means that when i hit the ball, it travels at a constant forward velocity but it's vertical velocity is constantly changing due to gravity. If i hit the ball with positive vertical velocity over the net, it travels upward but at a decreasing rate, due to the negative acceleration of gravity, until it reaches its peak and vertical velocity is zero. Its vertical velocity then decreases at an increases rate till the ball hits the other side of the table. All the while, its horizontal velocity remains constant. Luckily there was no wind in the garage to affect the projectile's path. Also, the wind resistance of the ping pong ball was not great enough to disrupt the projectile motion.

Soccer Ball Acceleration

This weekend i played a soccer game at waipio soccer park in the afternoon. Are team lost the game but in the process I realized that a soccer ball undergoes both positive and negative acceleration. As i kicked the ball during a goal kick it went from a velocity of zero to around 30 mph by the time it left my foot resulting in a very high acceleration. But, as soon as the ball left my foot at 30 mph it immediately began slowing down as it rolled across the grace. It traveled around 50 yards before coming to a complete stop. This decrease in velocity is an example of negative acceleration. To bad this physics epiphany did not help us win the game.