Physics Blog 7: Uniform Circular Motion

Uniform circular motion, though it may seem an abstract concept in class and on our worksheets, is actually all around us. It was even abundant during Homecoming Week. On the day to dress up as pirates and ninjas, I was a ninja equipped with a deadly pair of NUNCHAKU!! (the plastic kind you buy at Price Busters for like $1) I now realize that swinging my nunchucks over my head was creating UNIFORM CIRCULAR MOTION!!

It's hard to tell from the angle of the picture, but the foam nunchucks are probably swinging at a slight angle below the horizontal. This makes the center of rotation just a little below the top of the half I'm holding. The centripetal force is being provided by the tension in the string, which is clearly less than the string's maximum tension - otherwise it would break. The length of the string is also the hypotenuse of an imaginary right triangle, the horizontal leg of which is the radius of the circle of motion. If I knew the length of the string (L) and the angle below the horizontal (A), I could calculate the radius (r) using r = (cosA)/L. If I were also given the linear velocity of the nunchucks, I could calculate the angular velocity using v = rw. PHYSICS IS ALL AROUND US!! :D

Physics Blog 6: Collisions

I was thinking about collisions in real life when I saw the perfect topic for my blog on TV: the Texans vs. Titans game! I was going to go find some footage of tackling in football when Cortland Finnegan and Andre Johnson provided me with all the footage I needed:

Collisions

When the punching starts, Andre Johnson's fist clearly has more momentum than Cortland Finnegan's face, as Finnegan's head bounces back every time Johnson strikes him. This means that, since the equation for momentum is p=mv, Johnson's fist has either greater mass or greater velocity - in this case, it is less massive than Finnegan's head and therefore must have far greater velocity. Additionally, both players exert enough force to overcome the friction between each other's heads and helmets and tear the helmets off at the onset of the fight. It's exciting to see physics concepts at work!! :)

Physics Blog 5: Picture Poses

This past week was Homecoming, and there were probably hundreds of possible topics for blogs. However, I really noticed physics at work when we were taking a group picture:

You can see on the right hand side that my friends Val and Andrew and I were holding Kevin motionless in the air. To achieve this, we had to offset his weight with the force we were applying from beneath him, and since he was not touching the ground, our three forces combined had to equal what the normal force would have been. If you look at other people in the picture, you can see other examples of the normal force being replaced with an equal force. PHYSICS IS FUN!! :)

Physics Blog 3: Hiking

A couple weekends ago I was camping with my family and some family friends at a beach house in Waialua. While racking my brain to come up with an idea for a physics blog, I recalled a hike we went on above Dillingham Airfield. The path itself was pretty steep and it made for a moderately challenging hike, but I can now look back on it with the greater understanding afforded by PHYSICS! Here is a picture taken by one of my friends during the hike:

If I were to draw a free body diagram of myself in this picture (pretending that I'm not pushing off of the earth, thereby increasing the normal force), it would have these elements:
- An incline of maybe 50 degrees
- Weight vector straight down of 9.8m (m being my mass)
- Normal force perpendicular to the incline of 9.8mcos50
- Friction equal to the normal force times the coefficient of STATIC friction (I'm not sliding)

In reality, there would be a push force from my steps but we don't really know how to implement that because it would increase the normal force; however, the push would have to offset the x-component of the weight vector and the friction in order for me to move at a constant velocity.

Enjoying nature is even more fun with a deeper understanding of physics!! :)

Physics Blog 2: Golf

A few weekends ago, I went golfing with some family friends at Mid-Pacific Country Club. Searching my mind and my camera for an idea for this blog, I came across the pictures from that day and was struck by the physics that were obviously involved in golf. In terms of what we're learning now, the golf ball leaves the tee when struck on a vector; in other words, it has both magnitude and direction. This picture is of my friend's dad on the driving range and shows the swing involved in getting the ball going:



Here is a close-up of what happens when the driver contacts the ball as it sits on the tee:



In this picture, it looks as if the ball is taking off at an angle of maybe 20 degrees with the ground. I don't have a way of measuring things like the initial x or y velocities based on this picture, but with my knowledge I would estimate that the ball leaves the tee with an initial overall velocity of about 80 meters per second. Once in the air, the y-velocity of the ball is constantly subjected to the acceleration of -9.8 meters per second squared provided by gravity. However, the x-velocity remains constant the entire time. The ball ends up following a roughly parabolic path; I say roughly because wind and air resistance factor into the actual path the ball takes in the air. Thus, recognizing physics concepts at work in golf is easy once you're familiar with them.

Volleyball Attacking

This past summer, my club volleyball team competed in the USAV Junior National Championships in Austin, Texas. Volleyball, like every other sport, provides a ton of examples of physics at work. Attacking, which is comprised of the setter setting the ball and the attacker hitting it, is one area where it is easy to see physics at work:

When the setter (15) sets the ball, it leaves his hands at an initial velocity, and the moment it leaves his hands it is in free fall. Thus, the ball is going to travel upward, accelerating at a rate of -9.8 m/s squared, reach a peak, and then travel downward, accelerating at a rate of 9.8 m/s squared. It's the attacker's job to hit the ball as close to the peak as possible:

Here the ball is going to leave the hand of the attacker (13, me) at an initial velocity and then decelerate (or have negative acceleration) due to air resistance and move downward (not upward first, since the trajectory is already downward) due to the constant pull of gravity:

During all of this, the actual jumping also demonstrates physics (as we learned in our lab last week). The body is in free fall from the moment it leaves the ground, which results in a symmetrical, parabolic position vs. time graph, just like a volleyball that has been set. In the video linked below, the first clip shows the effect of gravity on jumping; the second clip shows the effect of gravity on setting; and the last clip is just there because Clint has a RIDICULOUS save:

http://www.youtube.com/watch?v=3le-5S6OL7Q

Thus, it is easy to recognize the concepts of physics that are demonstrated in this aspect of volleyball.