This is a picture of a speaker that uses a variable resistor in the sound knob to control the volume of the sound it produces. The resistance on the electrons flowing through the speaker changes as the knob is turned. When the knob is turned, a strip of metal or other conducting substance is moved, forcing the electrons to travel a longer path than before. According to the resistance equation, extending the path also increases resistance. When resistance is increased, less electrons reach their destination per second and less sound is produced.

The Physics of an Air Filter

This is a picture of an air filter in my house that is meant to capture harmful materials in the air such as dust, cotton, and pollen. The filter is able to do this through the use of technology that is related to what we are learning in Physics right now. Near the front of the filter is a grill, which is called the "corona discharge" and is meant to ionize particles in the air. This electrical field gives extra electrons to the neutrally charged particles in the air. Because dust and other harmful substances are usually large, they are the ones who gain the negative charge produced by the "corona discharge." Further into the filter there is a metal plate with a strong positive charge, to which the now charged particles in the air are attracted to. With most of the harmful materials gone, clean air can flow from the top.

Torque

In the case of a fire, a firefighter would hook up a hose to the valve of this hybrid fire hydrant. He/She would then turn the red wheel to allow the pressurized water in the hydrant to be pushed through the hose and onto the fire. This task would be very difficult without special tools since the wheel's diameter is very large, it is pulled tightly to prevent pressurized water from bursting out of the valve, and is rusty. To turn the wheel, the firefighter would have to exert a significant torque. If the firefighter could not exert enough torque, he/she could increase the lever arm by attaching a clamp to the wheel with a bar attached. The firefighter could then push on the extended bar to turn the wheel, as the force necessary to exert a specific torque is inversely affected by the length of the lever arm.

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.