In these video, I demonstrate how constructive and destructive interference works with waves. I use water as the medium of the waves to travel. In the first video, I show how waves look without interference. In the second video, I show wave interference in water and show how it affects the waves. In the video, you can see that the waves continue to move through each other, but in certain locations, the amplitude of the waves increase because of constructive interference. Constructive interference is defined as when two waves meet and create a greater amplitude equal to the sum of their amplitudes. In the video, there are also points of destructive interference even though they are harder to see. Destructive interference is when two waves meet and create a smaller amplitude equal to the sum of the two waves. Destructive interference happens because when the two waves meet, one will be at a position that is less than equilibrium and the other will be at a point greater than equilibrium. Equilibrium is the point where the water would be if there were no waves. If the two positions are opposite, destructive interference can cause the two waves to completely cancel each other out and leave the water stuck at equilibrium. In this example, there is both destructive and constructive interference.
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A lacrosse shot incorporates almost all aspects of physics that we have covered this year. The speed of the shot is dependent on many of these aspects. I will go over how each of these aspects affects the speed and/or trajectory of the shot. MomentumBefore the shot, I start with a crow-hop to get linear momentum prior to shooting. By planting my foot into the ground as I start to shoot, I transfer my linear momentum into rotational momentum of my body to increase the speed in the shot. This rotational momentum helps me swing my arms and the twist my body to create maximum speed of the shot. The crow-hop is important because without the transfer of the momentum that was gained from doing it, the shot would be much slower and it is why if you are standing still, your shot will go much slower. EnergyEnergy matters in the lacrosse shot because of the transfer of energy throughout the shot when running up I have some translational kinetic energy and a lot of potential energy, but through the rotation of the shot it is transferred into rotational kinetic energy. It is important to transfer as much of my energy into rotational kinetic energy because that is where the power of the shot comes from. Torque/RotationsAn important part of the lacrosse shot is the torque. When you shoot, you exert a torque on the stick that gives the shot its speed. The torque arm (radius) is very important in the shot because the further you extend your stick away from your body when you wind up, the faster the shot will go. This is because the torque arm is proportional to the torque given the formula, torque = radius * force sin(theta), so it is very important to extend your arms and put your hands near the bottom of the stick as you shoot to increase your torque arm or radius. Force Diagram of the Ball During a Lacrosse ShotForcesWhen shooting in lacrosse, you apply a force on the stick by pushing towards the goal with your top hand and pulling your bottom hand backwards creating rotational motion of the stick. Its important to apply a large force after you pull the stick back to wind up because it will create a faster acceleration of the stick which will cause the shot to go faster. The forces of the push of the top arm and the pull with the bottom arm are in the same direction even though they seem to be opposites. It is important for these forces to be large because the greater the force, the greater the acceleration of the stick during the shot, which will cause the ball to be released at a greater speed. Also, the frictional force between the stick and the gloves helps you hold onto the stick and gives you grip as you shoot allowing you to shoot as fast as possible. Projectile MotionProjectile motion is important in lacrosse shots because of aiming the shot. After you shoot the ball, it has an acceleration of -9.8 m/s/s. Because of this, you must aim for above where you want to hit on the net. To give an example of how much above the target you must shoot, I will say I shot a ball at 36 m/s from 10 m away from the goal which is a normal speed and is about the same distance as the shot shown above. To calculate how much it will drop, I first have to calculate how much time it would take for the ball to reach the goal. To do this I will use X=vi*t+1/2*a*t^2. Acceleration is zero because I am ignoring air resistance so it is (10 m = 36 m/s * time). If I divide both sides by 36, I can conclude that it would take about 0.278 seconds for the ball to reach the goal. Using this I can use Y=vi*t+1/2at^2. Knowing that vi in the y direction is negative, I can solve for Y. Y=.5*-9.8*0.278^2. Calculating this, I get that the ball will drop 0.378 m during the shot, so I must aim 0.378 m above my target. This is important to understand because without it, my shot would have hit the goalie right in the stick in the shot shown above.
The right hand turn before was dangerous because is requires a larger centripetal acceleration and force than afterwards. This is because radius and centripetal force have an inverse relationship that is shown in the centripetal force formula Fc=mv²/r. This makes sense because the turn is less sharp because of the greater radius, so it takes you a longer distance to complete the turn. Centripetal force is the force that causes circular motion that is always pointing towards the center of the circle. In this circumstance, the centripetal force is a frictional force between the car's tires and the ground. When the road is icy there is less friction between the tires and the ground which can make the original turn very dangerous and could cause the car to skid into the intersection because the centripetal force is not great enough to complete the turn. After the change, the greater radius of the turn makes there be less friction required to make the turn so cars are less likely to skid into the intersection.
I feel alright about the way that the test went. It was about as hard as I expected and was much harder than a normal physics test. I felt like it was challenging because many of the questions seemed like they were written to trick you and also some of the questions were very difficult and specific. Some of the basic free fall motion questions were easy to me. I felt prepared for it even though i felt like it was challenging. I studied a decent amount and i felt like I was going to do well. I studied by looking at peoples study guides and looking at my quizzes. I feel like these helped me when I was taking the test.
I feel like I am in the right place in this class. I am concerned about all of the website things because sometimes they can be confusing, but i feel like I am ready for this class. I feel like I am good at the type of things that physics require and I will be ready for this class. I do not want to drop this class and I won't. I accidentally deleted this post and I am reposting it you already graded it.
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AuthorPhysics student at Flint HIll Archives
April 2019
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