Just yesterday in class it seemed everyone had a good time racing some cans that they though would go the fastest. However, there were a few unexpected victors in the bracket as we saw the two walk-ons: Orange Gatorade and Mr. Temple's water bottle reach the finals, with the Orange Gatorade getting the dub in 3 matches. Why was this?
In general, we know that the higher the mass and radius of the can, the faster it will go (i.e. its Moment of Inertia). We know the moment of inertia of a cylinder is MR^2, thus the radius having a much larger impact on the can's inertia that its mass ultimately. If we judged the races by each can's moment of inertia see who would in, chances are that Miss Huppe's German Potato Salad (GPS) would've brought home the gold. However, the Orange Gatorade knocked out the GPS for some reason or another, even though the GPS has a higher moment of inertia as well as an initial potential energy. After some class discussion we realized that there was a direct correlation between the density, or state of matter inside, and the success of the can/cylinder. The proper term for this difference in thickness would be the substance's viscosity. A substance's viscosity is determined by its resistance to flow. For example, maple syrup would have a much larger viscosity than water would. Therefore, if you had two equally filled identical cans - one with maple syrup and one with water - the one with water would go the fastest each time. This is because when a substance is more viscous than another, there will be more residue on the top of the inside of the can than the other. If you were to fill a clear water bottle partially and watch it roll down a ramp, you would see that the water would settle to the lowest point of the water bottle. The Orange Gatorade's traveled faster than the GPS and all its other opponents because of its state of matter inside which allowed it the least resistance and loss in energy during its motion.
Even when we thought we knew which was going to win, the underdog claimed the victory!
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.
There is a video from awhile back that always makes me think about how good some soccer players really are. One skill that I believe exhibits complete mastery is curving or "bending" a soccer ball from a stationary free kick (at rest). Obviously this is not just some weird thing that happens, there must be a reason that physics can explain behind it. Upon further research there is; it is called the "Magnus Effect." This is done when either a clockwise or counter-clockwise spin is imparted on the ball. In the example below, the player hits the ball with a counter-clockwise spin, creating a small air field around it that travels in the same direction. As it goes through the air there is air resistance that is exerted on the front of the ball, slowing it down, and a force on either side of this air around the ball. the air that strikes the right side of the ball is slowed down by the counter-clockwise spin of the ball and it's effect on the ball is decreased in magnitude. The force of air on the left side is tangent to the circular path of air around the ball, so there is an added spin to the ball. This pushes the air off to the right and because Newton's laws say two objects exert equal and opposite forces, the ball will push off to the left, resulting in something like the videos below.
Most people have played with a slinky before, it goes down as one of the most classic yet simple toys of all time probably. My dad told me the other day about it being the 70th anniversary of the slinky being up for public sale. The story goes, the inventor - Richard James - thought of the idea when he was using springs to create instruments to stabilize boats in rough seas. While doing this he accidentally knocked a spring off of a shelf and watched as it fell down the stairs in a graceful manner as opposed to tumbling down.
The Slinky demonstrates the effects of friction and inertia, potential and kinetic energy. Since inertia determines how resistant an object is to a change in motion, this clearly has pertinence in the motion of a slinky. This resistance to a change in motion, which is greater in metal slinkies than plastic ones, keeps the object moving down the stairs. Friction plays a role in the motion of the slinky as well because as the slinky falls down the stairs, the bottom of it does not move when it hits the next step, thus containing the object's momentum on the top part of the slinky - propelling it to the next step. There's also a clear transfer between potential and kinetic energy in the slinky's fall. As the slinky starts with an impulse from its rightful owner, it has potential energy in relation to the next step down. Once the slinky makes contact with the next step this is converted to kinetic energy which will propel it to the next step, and so on.
All in all, the physics behind the slinky is relatively simple, but no one can deny that it's fun to push one down the stairs and watch it go.
Greetings Comrades,
Fall has many seasonal activities that come with it. One of these that I find rather unpleasant is raking/blowing leaves, due to its apparent futile nature. This past weekend, since my dad purchased another leaf blower, we were both able to use one and cut the time in half nearly to do our house's leaves. However, using a leaf blower can be frustrating due to the forces of air resistance and wind, which take away a substantial amount of kinetic energy from the leaves.
Even the highest power of leaf blowers only blow at speeds of 120m/s. So theoretically, if the leaf were in the air for 1 second, the leaf should go 120m (neglecting air resistance). In this instance, air resistance causes the leaf to only go maybe 12m. Not only is it frustrating to see more leaves falling where you just cleaned up, but the fact that the leaves only go a short distance makes it even worse.
Part of the reason the leaf experiences so much resistance is due to its surface area. Air resistance is largely determined by the amount of air molecules an object collides with in its intended path of travel. For example, if you took a marble and a leaf (of equal mass) and dropped them from a height of 20m, the marble would hit the ground first every time. Why is this? After doing some intense research, I believe it's because the leaf is making more "collisions" with the air molecules which slow it down more than the marble. It would take more of these collisions for the marble to reach its terminal velocity due to a lower area of contact, whereas the leaf reaches its fairly quickly. Th leaf's shape essentially causes it to be displaced less by the impulse from the leaf blower.
Looks like I'll have more time to ponder such thoughts in the future, as my lawn is coated in leaves currently.
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!
