In this unit I learned....
ACTION-REACTION PAIRS AND NEWTONS 3rd LAW
Newtons third law states that for every action there will be an opposite and equal reaction. This was a little confusing at first because it was difficult for me to wrap my brain around the fact that a bicycle hitting a large truck would exert the same amount of force on the large truck as the large truck exerts on the bicycle. However, the bicycle would have a larger acceleration because as we learned in previous lessons, f=ma. Therefore, in order to equal the force of the larger truck the bicycle will need a larger acceleration.
We can use action-reaction pairs to further understand newtons third law. However, non action-reaction pairs can still experience newtons third law. A perfect example of this would be book sitting on a table. The book and the table are action-reaction pair because the book pulls up table up while the table pulls the book down. The table and the book would be an action-reaction pair. The book experiences a similar force with the ground, however they do not form an action reaction pair. This is because of the table. Because the table is existent, the book and ground do not form a pair.
as shown, the person on the right is exerting a larger force on the ground than the person on the left.
VECTORS
Vectors proved to be one of the most difficult aspects of this unit for me. Although now they are simple to me, my misunderstanding of how they worked transitioned into our studies of the conservation of momentum, proving to be slightly detrimental. However, now that I DO understand how vectors work, I am able to also understand other aspects of unit 3. So what are vectors?
We generally use vectors when we are determining where something will go when it is being pushed from different directions by different forces. Through using vectors, we are able to discover the exact direction that an object will move while being pushed in different directions. One of the most common examples of a problem like this is a boat on a river that has a force pushing the water downstream. However, the boat wants to get to the other side. By going straight across, the downstream force will play a role in the boat's direction and cause it to go diagonally downward/to the other side. I know this because when you draw a vector, the direction can be determined.
as shown here, with the current the boat will go diagonally. We can determine this direction through vectors!
Another example:
another real life example of how vectors can be used is, why when we sled, do we slide down the hill?
This is because when someone is sledding down a hill, the f-support is pulling the box upward, while gravity is pulling it downward, through using vectors, we can find that the f-net will meet perfectly in the middle going down the hill.
GRAVITY AND TIDES
Gravity is the most prominent forth that we experience in our universe. Gravity offers an explanation to almost everything as it is gravity that causes our feet to stay on the ground, and tides in our ocean.
The fundamental force for finding gravitational force is f=G(m1m2)/d^2. G=
Also, force depends on two major things. Distance, and mass.
So why do we have tides? Tides are actually caused because of gravitational force. The sun exerts a very large force on earth because of it's mass, and also the moon does as well because of it's closer distance. So how do these gravitational pulls cause tides? Tides are caused by the difference of force felt by opposite sides of the earth.
There are two major types of tides. Spring and Neap tides. They cause higher highs and lower lows.
They occur when the moon is in different relation to the earth.
Momentum and Impulse relations
The definition of momentum is something's mass times it's velocity.
the symbol we use for momentum is p
The symbol we use for change in momentum is delta p.
delta p=pfinal-finitial
The definition of impulse is force times the change in time
the symbol for this is J
delta p=J
Therefore the change in momentum equals impulse!
so...also delta p=f delta (t)
EXAMPLE PROBLEM! find the force when....
final momentum=120 kgm/s
initial momentum=100 kgm/s
time=5s
solving
pfinal-pinitial=f delta t
120-100=f(5)
force=4N
Why do bungee jumpers use stretchy rope?
p=mv No matter how it is stopped, the bungee jumper will go from moving to not moving
delta p=pinitial-pfinal the change in p stays the same
J=change in p because J=delta p, the impulse will also stay the same.
J=f times the change in t
j=f change in t
j=f change in t The springy floors will increase the amount of time it will take the jumper to stop moving therefore, the force will decrease.
Conservation of momentum
as I mentioned previously, momentum=mass times velocity
We also know that because of newtons third law, in any form of collision, the forces will be equal and opposite.
Fa=-Fb
Fa(change in t)=-Fb(change in t) IMPULSE!
Impulse=change in momentum!
no net change in momentum
Practice:
if a 2kg cart moving at 10m/s runs into a stationary 5kg cart moving at 0m/s
how fast will the 2kg cart push the 5kg cart after they are hit together?
ptotal before=ptotal after
pa+pb (before)=pa+pb (after)
MaVa+MbVb (before)=MaVa+MbVb (after)
2(10)+5(0)=2(0)+5(Vb)
Vb=4m/s
another examples would be when the cart runs into another cart AND STICKS and move as one unit. A problem like this would be approached the exact same way, however, in the formula MaVa+MbVb=MaVa+MbVb, you would combine the masses, eventually ending with the formula
MaVa+MbVb (before)=Ma+Mb(Vab)
WHAT I HAVE FOUND MOST DIFFICULT
This unit has probably been the most difficult for me. I have struggled with almost every concept that we have covered, particularly the conservation of momentum. The conservation of momentum was extremely confusing to me, and I'm not entirely sure why. However, to overcome this problem, I got my friend Catherine to tutor me so that I can fully understand the concept for the test. She took me step by step through practice problems, individually explaining each step. Although this took time, it did eventually make the light bulb turn on.
Problem solving skills, effort and learning
I think that for this unit, my effort could have been better. Because I got so frustrated with the material, there were times that I would give up because I did not understand. However, towards the end of the unit, I really put forth the best effort I possibly could to make sure I understand all the material. In homework I don't think I did as well as normal, however, I did always try and do my homework. Activities and blog post: I think I certainly put forth my best effort.
I think that my problem solving skills are certainly improving as we begin to solve more complex problems. I continue to have the problem of forgetting to write all the formulas/lines/information needed on quizzes and tests, however as I practice more and more, I become much more conscious of what I need to write down for each problem. I think my creativity is also getting better, because the more I spend on blog posts, the more I can improve. Also, to understand material, Catherine and I used very creative ways to get the points across. I don't think that my collaboration with my group members has really improved. For the last podcast we were unable to meet so I ended up doing the entire thing. Although this was partly because we ran out of class time, and our memory card broke, I hope to work more with them next time because the podcast ended up taking me about 4 hours.
Connections
I think that what is really so remarkable about physics is it's direct application to EVERYTHING that goes on around us! Every single aspect that we have learned in this unit, and this year, have applied to reality. In this unit, it was very interesting to learn why tides happen. Whenever I am at the beach I always wonder. Although I knew that the moon played a role in it, I was unaware that tides are actually caused by the CHANGE in force on opposite sides of the earth. Gravitational force also effects us daily as it is present in everything we do. Newton's third law and the subjects that follow underneath that title, threw me off because I did not know that for every action there is an opposite and equal reaction, however, now that I understand it can be applied to real life. For example, how do you when an egg toss? Why do gymnasts use bouncy floors?
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