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.