Blog Reflection 2-17

Summary
Difficulties
overcoming the difficulties
relate it to real life


In this unit we learned about work and energy, and the relations in between the two.  Work is a function of how much force you put on an object, and the distance over which that force occurs, using the formula Work=Force x Distance.  Work is measured in Joules.  Power is related to work, in that work divided by the time (in seconds) that it takes place over will give you the power generated by that action.  For example, if you do 1000J of work over 5 seconds, that will be 200 watts of power.  Kinetic Energy is related to work, in that the work done on an object is equal to the change in kinetic energy of that object.  The formula for finding kinetic energy without knowing the work is KE=1/2 mv^2.  Potential Energy is sort of like Kinetic Energy's evil twin.  If an object has an amount of potential energy (found using the formula PE=weight x height), than as it releases that potential energy, it is transformed into kinetic energy.  Machines are devices used to decrease the amount of force it takes to do a certain amount of work by artificially increasing the distance.  However, you cannot get more work out of a machine than you put into it.

Some difficulty I had with this unit was remembering all of the different formulas.  I mostly managed to remember by simply going over them repeatedly, but I didn't quite manage to memorize the formula for potential energy.

This unit is one of the most connected to real life that we have had for a while.  It teaches us about the energy things have while they are in motion, as well as how machines function.

Work Resource

This is a video from Khan Academy about an introduction to work and energy, and how they relate to one another.  Khan Academy do very good tutorials, so this is a comprehensive lesson on the subject.

Unit Blog Reflection

Unit Blog Reflection

This unit I learned a lot about things that spin around, such as their angular momentum, which is the quotient of the rotational inertia and the rotational velocity.  Rotational inertia is the “laziness” of a rotating object, or it’s resistance to being spun faster or slower.  If something has a lower rotational inertia, but the same energy as something with equal mass, it will spin faster even if they both started with the same rotational velocity.  Rotational velocity, meanwhile, is how fast something is spinning, and is directly influenced by rotational inertia.  The angular momentum will be the same regardless of whether the object is spinning quickly with a low rotational inertia, or if the object is spinning slowly with a high rotational inertia.  I also learned about the different kinds of velocities when an abject is spinning.  Rotational velocity is one of them, but there is also tangential velocity, and they are very different.  For example, if two gears, one small and with 10 teeth, and the other one large and with 20 teeth, are interlocked and spinning together at a rate in which the larger one spins once per second, they will have the same tangential velocities, because they are both spinning at a rate of 20 teeth per second, even though that is two rotations for one of them and one rotation for the other.  However, because one of them has to spin twice as fast to have the same tangential velocity, it therefore has a higher rotational velocity.  We also learned about torque, specifically the effect torque has on your center of gravity and the amount of force you can apply to an object.  

Meter Stick Blog

     The meter stick, when it is balanced on the table, does not have a torque because each side of the meter stick has a torque, but in opposite directions (clockwise vs counterclockwise), so they cancel out.  The center of gravity of the meter stick changes when you add the 100 gram weight, in order to ensure that both sides (when balanced) have the same torque.
     To figure out how much the meter stick weighs, we (me and Manuel) measured where the new center of gravity was with the weight, and it was 24.4 cm from the edge of the meter stick.  The center of gravity for the meter stick was 50.6 cm.  We had to find the torque of one side of the meter stick, so we used the one with the weight on it, where we knew both the force downward (9.8 times .1) and the lever arm (.24).  Using those numbers, we got the torque as .239 N.  We then plugged that number into the other side, with the equation .239=(.506-.244)(Force), with Force being the weight of the meter stick.
     With this equation set up, all we had to do was solve it, then convert the answer from .912 Newtons, to grams, which gave us the answer of 92.85 grams.  The actual weight was 92.1 grams.
   

(Labelled drawing in progress)

Torque Resource

The video is from a series that contains tutorials on various different subjects, namely Khan Academy and this one is on the subject of torque.  It is really just a video that will teach you about torque through use of a sort of digital blackboard to illustrate the lessons that the narrator is giving.

Rotational Inertia resource

This video shows a spin from an ice skater that, when she tucks in her arms and legs, reaches up to over 300 rpm.  I thought this was a very good video to show off rotational inertia, as it is very clear that she is able to reach those speeds only after tucking in her arms and legs.

Unit Reflection Unit 3

Unit Blog Reflection

A. In this unit I learned about the concepts of gravity and momentum.  This includes vectors, action/reaction pairs and conservation of momentum.  Gravity is the force that everything gives off, and it causes everything to interact with everything else.  The formula to determine the strength of gravity is F=Gm1m2/d-squared.  Momentum is the force an object has, you calculate momentum with mass times velocity.  Vectors are lines that show the direction and magnitude of an object’s projected path.  Action/reaction pairs are, well, everything, because everything is affected by everything else and Fa     = -Fb  .  Conservation of momentum states that momentum never disappears, it is just transferred into different objects. 

The things that I have found difficult about this unit are all of the particulars for how you answer each problem, especially when it comes to vectors.  If you mess up on answering any part, you start losing points.  I haven’t overcome these difficulties quite yet, but when I do it will be because of excessive repetition.

My problem solving skills, I feel, are fairly good, apart from the situation I described last paragraph.  My effort towards homework could be much better, I will work on that in the future.  My effort in activities is around the average, the activities themselves are very interesting, and the mathematics aren’t too complicated.    My effort towards blog postings is average as well, given that they are often more fun to do than regular papers.  I have been learning, although some stuff I still need to work on, but I do know most of the material.

B Momentum is one of the big things that physics connects to everyday life, whether it’s a car accident or sailing a boat across a moving river, momentum in one form or another governs the behavior of such objects.  Gravity is an even more universal concept, as without it the universe as we know it would stop existing.