This
unit was about Newton’s third law, which says that for every action there is an
equal and opposite reaction. The unit was sectioned off into categories which
include action and reaction pairs, momentum and its relationship to force,
forces in perpendicular directions, gravity and tides, and the conservation of
momentum.
According to Newton's third law, for every action force there is an equal and opposite reaction force. Forces always come in pairs - known as "action-reaction force pairs." Identifying and describing action-reaction force pairs is easy all you have to do is simply identify the two interacting objects and make two statements describing who is pushing on whom and in what direction. For example, consider the interaction between a horse drawn carriage (known to my class as the horse and buggy problem). Why is a horse able to pull a carriage? To answer problems of this sort (bouncy floors for gymnast) you must make sure to keep the same verb, directions must be opposite of each other, and the subjects have to stay the same. First we were to label all action and reaction pairs.
1.
Horse pulls buggy forward, buggy pulls horse
backward.
2.
Buggy pushes ground forward, ground pushes
buggy backward.
3.
Horse pushes ground backward, ground pushes
horse forward.
you must use this information to answer
the reasoning behind why the horse is able to move the buggy. The horse pulls
buggy with an equal force that the buggy pulls with. We know this because of
Newton’s 3rd law which says every action has an equal and opposite
reaction. The horse and buggy move forward in the horse’s direction because the
horse pushes the ground harder than the buggy pushes on the ground. The horse
is able to move the buggy because of its hooves which allow for friction on the
ground over the wheels.
The next thing we discussed in class was vectors in particular were adding non- parallel vectors/ and free body diagrams. The best example is which boat would get across the river first? The answer is a. We know this because we draw vectors with each arrow already provided to create a parallelogram and then connect the boat the farthest corner. A is the only option which moves with the current and goes straight across when the vectors are drawn.
We followed this section with force of gravity and tides. We learned the relationship between the force and gravity equals F=G(m1m2)/d2. So if distance decreases the force increases and if distance increases the force decreases. So, if the distance is doubled the force decreases by 1/4, and if you cut the distance in half you force increases by 4 times its original. We also learned about how tides are caused and which has the greater force: the earth and the huge sun or the earth and the closer moon. We learned that to calculate the force between the sun and the earth and the earth to the moon we had the use the equation F= G(m1m2)/d2, and then we plugged in. We learned that the greater force is between the earth and the sun and confused many of us including myself on how tides are caused. Tides are caused due to the location of the Earth. They are caused by the difference in force which is greater than the sun to the earth. They are caused by the difference in force felt by opposite sides of the Earth. We also learned that distance has a greater effect on the force than a change in mass and that everything with mass attracts everything with mass, and everything with mass has a force. This also relates to your weight on earth, so the closer you are to the center the smaller you are and the farther away you are the more you weigh. There are two types of tides; they are spring tides and neap tides. Spring tides are higher high tides and lower low tides. Spring tides occur when the sun and the moon are aligned. Neap tides are high low tides and the lower tides are higher. Neap tides are when the moon is perpendicular to the Sun and half-moons.
The next section focused on Impulse and its relationship to momentum. This section focuses on the big question; how airbags keep us from getting injured (or less injury). p=mv, and the change in p or delta p= pfinal-pinitial. P represents the momentum. The change in p is the same regardless of if you stop quickly or slowly. Impulse is force * time the force is applied. Impulse is represented by J. So J=F * change in time, or J= change in p. This section also related to; why are nylon ropes which stretch considerably under tension, favored by mountain climbers? The answer is; no matter how a person falls they go from moving to not moving (p=mv). Therefore the change in momentum is the same regardless of how they are stopped. (deltap= pfinal- pinitial). Since the change in p is the same no matter how it is stopped the impulse is also the same (deltap=J).The climber prefers nylon ropes because they are stopped over a longer period of time rather than being stopped right away (J=F*deltat) (J=-F*deltat). This causes the force on them to be smaller, the smaller the force the less likely to be injured.
Momentum is a commonly used term in sports. A team that has the momentum is on the move and is going to take some effort to stop them. Momentum is a physics term; that refers to the quantity of motion that an object has. If an object is in motion (on the move) then it has momentum. Momentum can be defined as "mass in motion." All objects have mass; so if an object is moving, then it has momentum - it has its mass in motion. The amount of momentum that an object has is dependent upon two variables: how much stuff is moving and how fast the stuff is moving. Momentum depends upon the variables mass and velocity. In terms of an equation, the momentum of an object is equal to the mass of the object times the velocity of the object. Momentum = mass * velocity. We then focused on the conservation of momentum. The conservation of momentum relates to Newton’s third law in that it is the absence of an external force, so if you wish to change the momentum of something you must change the momentum of the entire system. The more momentum that an object has, the harder that it is to stop. Thus, it would require a greater amount of force or a longer amount of time or both to bring such an object to a halt. As the force acts upon the object for a given amount of time, the object's velocity is changed; and hence, the object's momentum is changed. Force acting for a given amount of time will change an object's momentum. One focus of this unit is to understand the physics of collisions. The physics of collisions are governed by the laws of momentum; and the first law that we discuss in this unit is expressed in the above equation. The equation is known as the impulse-momentum change equation. The law can be expressed this way: In a collision, an object experiences a force for a specific amount of time that results in a change in momentum. The result of the force acting for the given amount of time is that the object's mass either speeds up or slows down (or changes direction). The impulse experienced by the object equals the change in momentum of the object. In equation form, F • t = m • Δ v. In a collision, objects experience an impulse; the impulse causes and is equal to the change in momentum. Collisions in which objects rebound with the same speed (and thus, the same momentum and kinetic energy) as they had prior to the collision are known as elastic collisions. In general, elastic collisions are characterized by a large velocity change, a large momentum change, a large impulse, and a large force.
What I have found difficult about what I have studied is getting the big picture and relating it to the real world in real word terms. I overcame these difficulties by discussing the material with my teacher and my peers who were well aware of the concepts. I also overcame these difficulties by beginning to explain bits and pieces to my peers and them filling in parts of the bigger picture for me. What made the lightbulb click? Well for one I’m unsure if there was even a lightbulb. I kind of just walked through the motions and for most of each section felt lost until I revisited my notes and course videos. My goals for the next unit are to review my notes after class and section and to ask for help sooner than later so that I am more prepared for test and quizzes. My problem-solving skills have improved in my opinion but I could still work on formulating my arguments to help my answers. My effort grade should be a 4 or 5 because I work very hard, by asking questions, helping my peers and being tentative. My learning in general needs to be worked on just by reviewing my notes sooner and preparing myself by possibly making note cards and familiarizing myself with the big pictures of each unit. My persistence has been found in my questioning and my answering of proposed questions. My self- confidence in physics is really low because I feel like I know the information than I sit in front of the test or quiz and pretty much blank.
