Torque

Last Friday, we learned the difference between circular motion and rotational motion. While with circular motion we could calculate centripetal forces, with rotational motion we can use an equation to determine torque, which depends on two factors: Force and Lever Arm Distance (T=F*r). In paddling, the more torque you can produce, the faster the canoe will move. In the picture, the measuring tape goes from the handle of the paddle to the typical place where your bottom hand should be. This is effectively the lever arm distance. Paddling coaches say to hold as low as possible on the paddle because as the lever arm distance increases, so does torque.

Impulse

Why is a foam football easier to catch than a leather one? I always had an idea that the foam football was easier to catch because it was softer and easier to grasp, but I now know the physics behind this innate idea. When a football hits your hands, it exerts a force upon you. To stop the football and hold on to it, your hands must exert the exact same force back upon the football to create a net force of 0 N and reduce the ball's velocity to zero. Impulse, defined as the change in momentum of an object, equals Force times time. With this information, you know that an extension of the time of a catch will decrease the force exerted by the ball at any given second. The foam football, which compresses as you catch it, exerts a smaller force over a longer time, while the leather football does not compress as you catch it, and thereby exerts a larger force on your hands over a shorter time period. This is why a foam football is easier to catch than a leather one.

Newton's 2nd Law of Motion

Now that tennis season is finished, I decided to write my journal about the physics involved in paddling, the sport I am doing now. In a race, the speed of the canoe is all important to winning. According to Newton's second law of motion, the acceleration of an object is equal to the net force acting on it divided by its mass. In the case of paddling, the net force on the canoe equals the sum force of everyone's paddle against the water minus air/water resistance. To increase the net force on the canoe, the paddler should be as strong as possible to exert more force on the water, but not too heavy, for as the paddler's mass increases, the boat' acceleration decreases.

1st Quarter Review Journal

For the first quarter at least, Physics seems to be better for me than Chemistry ever was. I decided to choose a picture of an eraser and corrective pen because I know that I need to make mistakes and work hard in Physics before I can master the concepts and succeed. Physics is a very interesting class, and the labs that we do are at the same time fun and applicable to learning the laws of nature. I also enjoy the Physics videos that we watch like Mythbusters and the Japanese game shows, because they show how Physics can be integrated into the real world in new and interesting ways. Though I find Physics interesting, I sometimes have trouble working with its equations; but I know that if I keep erasing and correcting, I will understand them in the end.

Position Graphs

This week, my family bought a new wireless mouse after our old one broke. Though I'm not exactly sure how a wireless mouse works, I think that it is based on the same technology that we used in our position graph lab. A usb receiver works with the laser on the bottom of the mouse in determining the pointer's position. As the mouse moves towards the computer (usb receiver), the mouse pointer moves upward on the screen. In the same way, the mouse pointer movers downward as you move the mouse away from the computer. This also works for moving the mouse right and left. This seems like a good application of Physics in improving technology.

Airsoft Gun Physics

This weekend, I decided to shoot my airsoft gun. Though I was'nt playing against anyone else, I just felt like practicing hitting targets. Like Adrian, my airsoft gun is an aeg (airsoft electric gun) but his is cooler. Even though I have a m4 and he has a G3SAS, our guns use the same principles of physics to fire bb's. When you pull the trigger, the gears in your gun push a coiled spring as far back as it can go and a bb is pushed up into the barrel from your clip by a hop-up system. The spring is then released, propelling the bb at a very fast speed from your barrel at your target. The speed is measured in feet per second (fps). In the end, the velocity of your bb as it comes out of the barrel depends on many factors such as: the quality of your battery, spring, or gearbox, or the size, weight, and type of your bb's.

Newton's Third Law of Motion

Journal 1: On Saturday, Sept. 6, I went to a tennis match between the Iolani Raiders and HBA Eagles. When the tennis ball is hit, Newton's third law of motion is applied. In his third law, Newton states, "For Every Action There Is An Equal And Opposite Reaction." When a tennis ball hits the strings of a tennis racket, the ball reacts by springing forward in the opposite direction. Tennis also can be used as an example for positive and negative acceleration. As the ball comes from across the net, it is moving in the positive direction with a positive velocity. Because of air resistance, the ball's acceleration is negative. At the point of contact between the racket and ball, the ball's acceleration becomes negative, then becomes positive as the ball slows down while moving in the opposite direction at a negative velocity.