Like many other students, I am looking forward to summer. One activity many people enjoy is water skiing! Water skiing has a lot of physics involved. The basics are essentially based on angles and gravity. When you get up from the start, your ski must be at a certain angle so that the water pushes down on the ski, creating a downward force that enables you to stand up (otherwise you'll just fall flat on your face). Once the forces up from the water and down on the ski are equal, you're set for takeoff!
Tension, a pulling force, is also involved when the skier holds on to be pulled by the boat. Once the tension in the rope becomes constant, you will travel at the same speed as the boat that is pulling you, since there is a constant force with no acceleration. Also, since you are usually moving in a circular path, there is also an inward, or centripetal force, keeping the you in a circular path.
Can't wait to go do it this summer!
Yesterday I was watching soccer on TV and saw Ronaldo notch a hat trick...yet again. However, I rather began to ponder the physics behind being a goalkeeper to stop shots - maybe not as perfect as Cristiano Ronaldo's. Physics can separate the good from the great goalkeepers.
Here are some factors in being a good goalkeeper:
1. Momentum- A goalkeeper must have his/her weight shifted forward, standing on their toes. When a shot comes, the goalkeeper will try to save the ball while moving forward. Therefore, due to conservation of momentum, they will deflect rebounds away from the goal as opposed to in the goal.
2. Vectors- While preparing for a shot, a goalkeeper must analyze vectors to determine a good place to stand - in the most probable path of the ball. If the forward is on the goal line (outside the goal) the goalkeeper should probably stand a step or two off his line, toward the back of the goal, to prepare for a cross (unless they have a crazy ability to curve the ball as seen in my previous blog on curve in soccer).
3. Impulse- The best goalkeepers always buy the most expensive goalie gloves. This is because not only they can afford this luxury, but the better gloves will increase the time the force of the ball is applied for, thus increasing the impulse. Not only will cheaper gloves be much less effective in helping the ball stick, but they will reduce the amount of impact time and increase the chance of a rebound (which is a major source of goals in the game of soccer).
I am not the best goalie clearly, seeing as I don't even play goalie, but I believe most keepers with a basis of physics knowledge would agree with me on this!
Recently I've had a little bit of a pickle fetish. However, one of the things that is inevitable for us regular pickle-eaters is the difficulty in taking of the lid of the jar.
One tip I have is to run the jar under hot water. This way the lid will become easier to turn. This is because metal has a higher coefficient of expansion than glass does. Thus, as the jar stays under the hot water, the metal expands a tiny bit, and the glass stays the same (I also find it easier to use my left hand because it's easier to turn CCW with your left than your right).
The other tip I have would be to hit the gym and organize a forearm based workout session because without the hot water trick I've got just about nothing.
Good luck in your future pickle jar opening endeavors.
Kobe Bryant just retired after 20 years at the Lakers. As a player straight from high school into the NBA he has set many records and is arguably one of the best basketball players of all time. One thing that him and other basketball players are known for is his jumping (which might not be as good as it was 10 years ago). I figured this would be as good a time as ever to analyze his jumping skills in two videos - one of him jumping a pit of snakes and dunking a ball, and of him jumping over a car (in my next blog post). Many believe that neither were real, so I'd like to discuss the physics of both stunts.
So the video above is of Kobe jumping a pit of snakes (I'd assume not venomous since other people were in the pit before him). After some statistics were found on this, it was calculated that his vertical acceleration was -9.56m/s^2, which is close enough to an object's acceleration due to gravity (9.81m/s^2). This evidence points to it being real, since air resistance should account for a decreased acceleration in either direction.
After scaling Kobe to the pool it can be concluded that the pool is about 12 feet across. Using various displacement measurements, The horizontal velocity of Kobe can be determined to be a little less that 12 mph - a realistic velocity as well.
Given the two data sets I can only assume that this jump could be realistic, since Kobe Bryant has a crazy amount of athleticism. I think that it could be real, but this one comes down to decision making - and I'm not sure Kobe would risk anything on a stupid (yet interesting) stunt.
In my previous blog I discussed the physics behind Kobe jumping a pit of snakes, which I believe is legitimate (or at least physically possible). Now I'd like to discuss another instance of Kobe's famous athleticism: him jumping over a car moving towards him. This one seems fake to me in theory because the consequences of the stunt are too much to warrant him doing it. However, I still think it'd be cool to think about the physics of it.
This one is definitely faked. If you were to scale Kobe like in the previous video and analyze the motion. His acceleration was -6.76m/s^2. This is 3 units away from the actual acceleration due to gravity. So something is telling me that there were strings of some sort attached to him allowing him to jump with a longer hang time and avoid the car. Could Kobe do it if he were feeling bold enough? I believe in his prime, with his vertical jump, he could do it. The only problem is that the car would need to be going fast. This would mean that his reaction times would need to be as close as 1/100 of a second or he would get hit or touched in mid-air. This is why I believe it is fake; it is physically possible, but in terms of probability and natural human error (please don't give me a 0 for this blog now!) I believe he wouldn't have done this.
The other day I was watching a soccer game, West Ham United vs Arsenal FC. I know I do blogs on soccer all the time but it's because I am just so fascinated by the things these players are able to do, hence why they are professionals. One of the players, Andy Carroll scored a bicycle kick, where a player flips himself/herself upside down with their foot in the air and kicking it over their head (sometimes referred to as an "overhead kick"). While this one was good, it reminded me of one from several years ago that another professional, Wayne Rooney performed in a game. Here's the video:
While this goal may still have you in awe (this happens maybe once every several years by the way), I'd like to start talking about the physics. So it all started with the crosser, Nani, who crossed the ball in at about 22 mph (the speed of an average cross). This speed of the ball means the reaction window for Rooney was microscopic, even to just put the ball on target - much less the upper corner of the net. A half second too quick or too slow and this bicycle kick will end up on the blooper section of sportcenter. Upon timing the jump, Rooney is in the air for about 3/4 of a second, meaning the margin for error is quite small. Rooney's foot has also been measured to be 1.80 meters above the ground (5'9") which is about the same height as Rooney. So you might ask, what is the advantage of doing this if he could've headed the ball instead? While this is normally what players do in this scenario, a header simply wouldn't have provided the same force (and thus acceleration) on the ball. This is because of the net torque on the ball. With a header, one really only uses a little less than half of their body to cock back and snap into the header to deliver a net force upon it. However, with a bicycle kick the whole body is involved. Since the body in midair experiences no outside forces, it acts as if it were a rotating object, where both halves of the body contribute to a clockwise motion to allow a well powered kick.
In addition, you will notice that he kicks one leg first and then the other. This has to do with momentum. as he generates momentum in one direction, this allows him to change the motion with the other leg and allow a greater velocity with his kicking leg before it makes contact with the ball.
All in all this stands as one of the best premier league goals of all time, ask anybody. It's really cool now to understand how Rooney did this (I know I never could)
