Impulse and Momentum of a Baseball

This video is a very quick summation of impulse and momentum. It talks about the equation for impulse, which is the force times the time, and it also tells us that impulse is equal to the change in momentum. The one thing that this video talked about that was different from what we learned in class is that the change is moment is equal to the mass times the change in velocity. In class we learned that the change in moment is equal to the final momentum times the initial momentum. Though these two things equal the same thing, it might be easier to stick to the one we learned in class. Other than that, this video is a really good short explanation and summary of impulse and momentum and how they relate to each other.

Tides Recourse

Unit Two Reflection

In unit two of physics, the first thing we learned about was newton's second law of motion. This law states that acceleration is directly proportional to force and inversely proportional to mass. This means that if the force increases, the acceleration will also increase. It also means that if mass decreases, the acceleration will increase. The lab that we did on this concept involved a cart, weights, and a hanging weight. We moved the weights around from the hanging weight to the cart and measured the acceleration on each change. In the lab, we constantly kept one thing concept. For example, we kept the force (or the weight on the hanging weight) constant and changed the mass of the whole system. Or, we kept the mass the same and changed the weight of the force (or the hanging weight). Through this, we found that acceleration is in fact directly proportional to force, meaning when one increases so does the other, and that mass is inversely proportional to acceleration. Meaning when one decreases, so does the other.

The next thing we learned about in physics was objects in free fall. In free fall, objects do not have air resistance and therefore only have the force of gravity act on it. The force of gravity is known to be 9.8 m/s squared. The two equations used when talking about free fall is velocity equals gravity times time and distance equals 1/2 gravity times time squared. We learned that acceleration is free fall is constant, meaning each second and object is gaining a speed of 9.8m/s^2. We also learned that in free fall, a penny and a feather will hit the ground at the same time because the only force acting on them is gravity. The lab that we did to demonstrate free fall was we used a steal ball to measure the height of third anderson. We did this by dropping the ball from the third floor, the top one, and recording the time it took for the ball to fall from the top of the floor to hit the ground. Using the average of a few different trails, we plugged this into the d=1/2gt^2 formula and found that our estimated height of third anderson was about 9 meters. Then, we took string and found that the actual distance was a little bit under 11, pretty close. 

The next thing we learned about was something similar to free fall but much more complicated. It's called projectile motion. Projectile motion is the affects on an object that does have air resistance and factors in the horizontal motion of an object. To get the horizontal velocity of an object you use the formula v=d/t. Of course, this can be rearranged to find the horizontal distance or how long an object traveled horizontally. Something that is different between vertical and horizontal velocity is that horizontal velocity stays constant throughout the time something is traveling through the air. However, vertical velocity gains 9.8m/s^2 each second when falling downward and looses 9.8m/s^2 when going upward. Projectile motion is used a lot when talking about skydiving. This is because when you are skydiving you are not free falling because you are greatly affected by air resistance. Once a person jumps out of a plane, they gain velocity as they fall until they reach something called terminal velocity. In terminal velocity, the weight of the object is equal to the air resistance on the object, causing the velocity to stay constant until something changes. This means that as the velocity increases, before terminal velocity, the acceleration is decreasing and is at 0 when the object is in terminal velocity. Once a parachutist reaches terminal velocity they can only stay there for a few seconds because they need to deploy their parachute on time in order to not get hurt when they hit the ground. The parachute helps the parachutist slow down, as we learned, because the two things that affect air resistance are surface area and speed. This means that the parachute adds surface area which also adds air resistance, causing the parachutist to slow down until the air resistance yet again equals its weight. However, this new terminal velocity is a lot slower than the original one due to the surface area of the parachute. Also, during this change the acceleration is not just decreasing but it is decelerating into the negatives. Projectile motion is not only used with parachutist, it can also be used with throwing things upward like shooting a cannon, throwing things downward like kicking a ball over a cliff, and dropping things out of air planes. The biggest example besides parachuting that we learned about was the difference between a falling piece of regular paper and crumpled up paper. Though it may seem like crumpling up paper could change its weight, causing it to fall faster, both of these things are incorrect. The reason that a crumpled up piece of paper falls faster than a regular piece of paper is simply due to surface area. Because the normal piece of paper has a bigger surface area, it is going to need more air resistance and therefore is going to take longer to reach a terminal velocity than a crumpled up piece of paper. 

What I have found difficult in what I have studied is separating each formula with each concept and not confusing the affects of gravity on an object in free fall compared to projectile motion. I overcame these difficulties, however, by really paying attention to each example and what they taught about the topic and how I could differentiate each concept by pairing them with their examples in my mind. 

My effort this unit, in my opinion, was even more than last unit. With the many different very difficult concepts we were learning I had to study even harder and make sure that I understood everything outside of class. Though this doesn't reflect in my grade, I felt pretty confident with the concepts because I understood a lot of the things we did in class. I thought that I problem solved pretty well in the labs and that I could express the concepts in both my spoken and written words. I tried to be patient with the work although at times it was difficult when the concepts became difficult, but altogether I thought that it was a strong unit regarding my work effort. 

My goal for the next unit, again, is to study more by completing every assignment on time even if I'm not 100% sure its right because I know now that learning from your mistakes is one of the best ways to learn.

Connections from this lab to everyday life are obvious; parachuting, things falling out of air planes, falling pieces of paper, exedra. But one thing that I noticed in everyday life that applied to physics that caught my eye was a balloon floating up to the sky. Though I'd seen it many times before, I had never though of the physics behind it. 

Falling Through the Air Recourse

In this video, the guy is asking random people if they think the heavier ball and the lighter ball will hit the ground at the same time or not. Most people, incorrectly, say that they will hit the ground at the same time because the force of gravity on both of them is the same. This is wrong because the heavier ball will fall faster in order to reach terminal velocity, a state in which the resistance and the weight of the ball are equal. This is because when air resistance is being factored in to something falling from the air, we know that acceleration is equal to the net force of the object minus the air resistance on the object divided by the weight of the object. Therefore, the heavier the object the faster it must fall in order to reach terminal velocity, while the lighter object reaches terminal velocity more quick, and is passed by the other object.

Physics when Punting a Soccer Ball

This is a picture of Michael kicking a ball straight up into the air. If we know that Michael kicks this ball with a velocity of 40 meters per second, we can figure out not only how long the ball is in the air, but how high it was at its highest point. Because the force of gravity is 10m/s, we know that the ball's velocity looses 10m/s each second. Therefore, to reach the top of it's path the ball must travel up in the air for 4 seconds. Then, since objects gain 10m/s each second when falling down, the ball will take 4 more seconds to return to Michaels foot. This concludes a total of 8 seconds. Then, using the distance formula (d=1/2gt(squared)) we can plug in 4 seconds, the point when it is the highest, to find out how high it went.
d=1/2gt(squared)
d=1/2(10)(8) squared
d=40 meters.

Free Fall: the Affects of Gravity

In this video Bill Nye is throwing different objects of different weights off of a parking deck and onto a target three stories below. The time each object took to hit the ground after leaving Nye's hands is the same, even though we didn't time it. You can tell this from watching the video, but also because we know that the force of gravity on objects is always 10 m/s squared, when you disregard air resistance. Because of this each object took the same amount of time to hit the ground.

Newton's Second Law Resource

In this video he is talking about the second law of motion and unlike the equation we use in class he uses the equation force equals mass multiplied by acceleration. He's using a red ball and a yellow ball and the red ball is heavier then the yellow ball. Therefore, they have a different mass. The force is the same and will be the same for both of the balls in the cannons with acceleration. You can physically see that the heavier ball was going far slower and lower than the yellow ball which was lighter. This proves that acceleration is inversely proportional to mass meaning the more mass the less acceleration and the less mass the more acceleration.