The Perfect Push-up

My dad has these workout things that you see on television: its called The Perfect Push-up. These handlebar looking devices are used to help you complete a push-up with proper technique, I suppose. (I've tried it and its not much easier than a normal push-up!) But I realized that these push-up things apply the concep to of torque.

Torque is a force that either causes or opposes rotation. Torque can be calculate by multiplying the lever arm, the distance from the axis to the point of the force, by the force exerted. In this case, a force causes rotation of the push-up devices which eases the tensions on your joints as you do a push-up. In this example, these handlebar things have a low moment of inertia. Moment of inertia is the measure of the resistance to the angular accleration. Moment of inertia equals the net torque divided by the angular acceleration. With the perfect push-up the moment of inertia is low because the net torque is low due to a small amount of force for them to rotate and a high angular acceleration because they rotate quickly. This low moment of inertia also contributes to the ease of the handlebars to make the push-up smooth and comfortable.

Crash!

At the end of summer, my brother got into a car accident. And this crash actually totaled our car. Luckily he did not get hurt, but I realized that his crash was physics related. He was on a freeway on-ramp in Aiea. This on-ramp was sort of like a loop (i think it was like 270 degrees). As he was turning, his car skidded and hit the railing. Apparently, many people had crashed in the same place before and there was many skid marks on the ground. (Someone five minutes before my brother had done the exact same thing!) This accident has to do with centripetal acceleration and centripetal force. Centripetal acceleration is the change in direction in a circular motion, and so velcoity is never constant. (centripetal acceleration = v squared/r) Centripetal force is the force that causes the circular motion and force is always directed toward the center. (centripetal force = m(v squared)/r) Centripetal force can represent different things in different situations. For example, centripetal force can represent the normal force, friction, or a combination of both. In my brother's example, the centripetal force was friction, but with the evidence of skid marks, it can be concluded that there wasn't enough friction, so there was not enough centripetal force to keep him in a circular path, which ultimately resulted in his crash. Also, his speed could have also contributed to the crash because in the centripetal force equation, a higher velocity directly results in a higher centripetal force required to stay in a circular motion.

Center of Mass: Basketball Techniques

This past weekend was the girls Iolani Classic. Teams from both coasts came to play, including the 1st, 2nd, and 4th nationally ranked teams in the nation. In the mechanics of playing basketball, the physics concept of the center of mass is used. While playing either on offense or defense, your center of mass is important. The center of mass (also the center of gravity) is our average location of your mass. At this point, it represents the mass of the entire object. Your center of mass can change and it does not have to be within the object. Playing on offense you want to stay lower than your defender so that you center of mass is lower, which results in quickness and speed. On the other hand, if you are on defense, you want to have a lower center of mass so that you can react faster to your opponent. The concept of center of mass is also very important in shooting the basketball. The proper mechanics in shooting includes feet pointing to the basket, shoulders square, and jump straight up, these all provide for a balanced body. If you follow these mechanics your shot should be good because your center of mass should be in the middle of you body (belly button area). As you can see in this picture, the player (school: Westlake) is trying to shoot the ball but her body is bent in like a "C". This is improper shooting technique. Her center of mass is outside of her body behind her torso becasue her arms and legs are behind her body. This creates a difficult shot becasue her body is unbalanced due to her change in center of mass.

UH Football Momentum

I went to the UH football game on Sat. when they played Idaho State. They killed Idaho really badly. Anyways, during the game I saw concepts that we have been learning in physics this chapter. In this picture, UH's offense is preparing for a snap against the defense of Idaho. When the offensive and defensive lines come crashing into each other this causes a sticky (also known as a inelastic) collision occurs. This means they stick together and their momentum is conserved. Also, right after the collision occurs, they have the same final velocity. When the lines do collide, each player has momentum, which is mass x velocity. So the player with the bigger mass and velocity will have the greater momentum. ( Thus most offensive and defensive lines are huge!) In the conservation of momentum, it states that when 2 things collide they transfer momentum so what one loses the other gains.

Energy on the Slopes

Here is a pic of me and my family when we went to Lake Tahoe. I am on the far right with the snowboard. (Sorry the picture is really blurry!) When we were on the mountain, we were actually experiencing physics. At the top, before we started going down, we had potential energy, which would equal mass times gravity times the height of our elevation to the lodge. This stored energy would be converted into kinetic energy as we started to move and this kinetic energy can be calculated as 1/2mass times velocity squared. At any given moment, because of the conservation of energy, our total energy (kinetic + potential) would always be the same (KE1 + PE1 = KE2 + PE2). So through the law of conservation of energy, the potential energy at the top of the mountain (no kinetic energy because we have zero velocity) should equal the kinetic energy (no potential energy because height is zero) I would posses at the bottom if I went straight down the slopes.

For the first quarter, I am really enjoying the class and all the labs. (it is way better than chemistry!) Some of the concepts with all the math is difficult, but after understanding it everything is much clearer. I think it is a challenging course, but I am learning a lot and am able to notice physics being applied in more aspects of my everyday life. My anxieties include remembering all the formulas and concepts and finishing the exams for the semester-final and even year final, especially since most of us take way more than a single period to complete our chapter tests. I think I am starting to adjust to physics and all the math that comes along with it. I think my performance and effort from this quarter can be improved. I really can improve on completing my homeworks and labs thoroughly. For the most part physics is like friction, it's fun!

My picture is of rock candy. Its hard, but sweet and tasty at the same time. If you break it into smaller pieces, its easier to swallow.

Basketball Projectile

Here is a pic of me when we played Punahou last season. (and we beat them!:)) As you can see, I am attempting a hook shot over my defender. This is a perfect scenerio to demonstrate a projectile motion. For the ball to go into the basket, the velocity of the ball, which break into the vertical and horizontal components must be perfect as compared to the distance from me to the hoop and the height of where I released the ball to the height of the rim. In a projectile motion, the horizontal velocity stays constant throughout because gravity or no other forces acts upon it. However, the vertical velocity is constantly changing due to gravity, so the object is always accelerating at -9.8m/s2. Also, in this case the angle at which the basketball is launched is a key component to making the basket. So to find the velocity of the ball, I would have to know the horizontal and vertical velocities and use the pythagorean theorem. (Too bad I didn't know physics then, because if I did I might have been able to make that shot!)