Unit 6 Reflection

Unit 6 was one of my favorite units so far this year. We learned about work, potential energy, kinetic energy, and many other things. First I’m going to talk about work, work=forcexdistance. The proper definition is; the product of a force and distance moved by the force. One thing to know is that in order for something to be doing work on an object the force and distance must be parallel. In other words, if you are carrying a 10 Newton book and walking a distance of 20 meters you are doing no work on the book. But if you push the book along the ground you will be doing 200 Joules of work (Joules is the standard measure for work). While talking about work we must talk about power, power=work done/time interval. Basically, the amount of time in which work is done, power is measured in watts.

Next came energy, which is defined as the property of a system that allows it to do work. We talked about potential and kinetic energy. Potential energy is present the energy that an object possesses because of its position. When an object has potential energy it is at rest, the equation for potential energy is PE= mass x gravity x height. The next type is kinetic energy, which is the energy of motion. The equation is KE= ½ Mass x velocity squared. A roller coaster is a good example of both because, the first hill is always the largest in order to get the most potential energy so when transferred to kinetic energy there will be enough to make it up the next hill.

The work energy theorem states that the work done on an object equals the change I kinetic energy (change in KE = work).

            Machines were the last thing that we talked about. A machine is a device used to increase or decrease the force you need to put in, in order to do a certain amount of work. One thing that is important when dealing with machines is the Law of Conservation of Energy, meaning that the work you put in equals the work put out (forcexdistance in = forcexdistance out). A machine lessens the force you need to put in to do this work by increasing the distance, therefore making your job easier. For example, when using a jack you only have to apply a little bit of force, but you must pump it a lot to only make the car move up a little (you increased the distance). A jack is a type of lever. The last thing you must know when dealing with machines is efficiency, or work output/work input. If a machine is 100% efficient that means that all of the energy was transferred and none was released. Efficiency is basically the percentage of energy you got out of what you put in.

            One thing that was difficult for me to understand at first was the idea that machines don’t change the amount of work you do. I felt as though machines made it to where you needed to do less work on an object and that’s why they made things easier. However, as I explained above they actually increase the distance, which decreases the force, thus making it easier to do the work. Problem solving was a big part of this section because all of the equations were related. We were presented with questions that gave us a mass of an object, the speed at which is was travelling, the speed it sped up to, and the distance it traveled. Then the questions had several parts. First we had to find the change in kinetic energy. Then the work done, which you had to know equals the change in kinetic energy. Next the amount of force applied, which you had to know the distance travelled and the work done, so you could use the work formula. Lastly, you were given a time in which this work occurred and you had to find the power. So, it was crucial that we had a solid understanding of how these formulas related. These concepts apply to real life for me, because they really helped me learn why things like jacks and pulleys work so effectively and how I could use this knowledge in the future to move heavy objects.

Mouse Trap Car Final Blog!!!!

As Race Day concluded, Paul and I came out victorious. There are a couple things that we had to account for in order to make a winning car. The first thing was Newton's First Law; an object in motion will remain in motion unless acted on by an outside force. Because of this law, we had to make sure we could decrease the presence of outside forces as much as possible. So, when the axle was jamming against the eyelets we used to hold it, we had to remove some of the tape to make sure this stopped happening. This prevented the forward motion of the axle from being hindered; therefore giving us smooth rotations, resulting in more speed. Also, we reduced the amount of friction acting upon the wheels by applying duct tape to the rims (CDs). The next thing we had to wrestle with was Newton’s Second Law; a=fnet/m. Paul and I made sure that we had the most acceleration that we could possibly create. So, we built a frame that has a small mass, using only paint stirrers as our bass. Then to get a large net force we built a lever-arm that is about 18 inches to get the most force that we could achieve. With the net force going up and the mass going down, we were able to get a pretty substantial amount of acceleration. Newton’s Third Law also came into effect, because it says every action has an equal and opposite reaction.  We figured out that the same force that the lever and string applied to the axle was transferred the wheels. The more force the lever creates, the more force applied to the axle, and then the more force on the wheels, creating more speed.

                The two types of friction present were surface friction and wind resistance. So, Paul and I had to make sure that we made the most aerodynamic car possible. to combat the wind resistance we made a slim, streamlined car. A bulky car would create more wind resistance and slow down the car. However, not all friction is bad. Surface friction between the floor and our wheels could actually help when we are trying to propel our car forward. By applying duct tape to the wheels we were able to get more surface friction, so our wheels would gain ground as soon as they began spinning. The only other problem related to friction was making sure that our axle stayed in place, keeping it from creating friction between it and the screw holders. That would decrease the force that was transferred to the wheels. All we did was apply duct tape on the axle to keep it from sliding in order to fix this, and then it was off to the races!

              As far as the wheels go, we decided to use blank disks. We chose these for a number of reasons. First because there mass is distributed evenly throughout, giving them less rotational inertia. Then we applied tape to make sure they were stabilized. One thing about the disks is that they are very light so alone on the axle they were not very stable, but two great minds such as Paul and I were able to fix that. We chose to put four wheels mainly just for stability. We started off with three wheels, but the car leaned to the slide and we realized that this would not be our fastest design. After we put four wheels the car stayed level and achieved greater speed. The wheels were also fairly large because the larger wheels can cover more distance in less time, and since this lab is all about time that was the best idea.

               The conservation of energy applies to our car, because when the lever-arm generates the force on the axle the energy conserved and is transferred to the wheels. The law of conservation of energy states that energy cannot be destroyed, and must be transferred to something no matter what. So we had to make sure that the energy was being transferred in a way that would be beneficial to our car. Applying duct tape to the axle in order to keep it in place, preventing friction from robbing us of some of our energy. In order to get the most velocity, we needed to generate as much kinetic energy as possible. Because since our car had a very low mass it would have to have a large velocity in order to get a lot of kinetic energy.

              Our lever arm was about eighteen inches long. We knew from our study of torque that we could generate more torque with a longer lever arm. Because, torque=force x lever arm, so we left the force the same (the force the mouse trap generated) and we just made a lever arm that was considerably larger than our opponents. This made the torque on the axle greater, causing it to rotate faster, and in turn the wheels spun faster, giving us more speed. We were able to do more work over a period of time, in other words generate more power due to our long lever arm.

         As far as rotational inertia goes we used disks so that our rotational inertia would be less. The mass of the disks is evenly distributed so that results in a lesser rotational inertia. Because they were larger in comparison to the others wheels they were able to cover more distance less time. Due to the greater tangential velocity, which was caused by the fact that the outside of the wheels had to spin faster in order to keep up with the center. The rotational velocity directly relates to how fast the axle is rotating. So, by generating a large amount of torque with our lever arm we were able to generate a lot of rotational velocity.

         We can’t calculate the amount of work the spring does because we do not know how to figure out how much force the spring generated (work = force x distance). Also the spring constantly changes position, and it moves so quickly that we would not be able to calculate the height at which it had potential energy; therefore we could not find the potential energy (mass x height). I believe that we could calculate the kinetic energy if we had a way to measure the speed of the spring. However, we don’t, so we cannot find the kinetic energy either.

         When we made our original design we really did not know what we were doing. As a result, our final design was a very upgraded version of our original design. Originally we were just going to use the mousetrap as the lever arm, but that changed because we needed more torque. Then we had to find ways to secure the wheels better, so that the wheels would not steal energy from the car (I explained how we did this in the first and second paragraphs). Some of the problems were wheel stabilization, generating enough force to get our car moving at blazing speeds, and reducing friction, all of which we were able to fix as I explained already. If I had a redo I would most likely try to find a more rigid lever arm, because ours bent which took some of the energy. If we could find one that didn’t bend I feel like that would have increased our speed exponentially. Also, we could have possibly found a better way than duct tape to stabilize the wheels. However, we came out victorious, so thought these changes would have been nice for more personal satisfaction, they were not needed to thrash the competition.

         

Mousetrap Car Construct Day One

On the first day of construction, Paul and I were not able to do very much because we did not have all of the necessary supplies needed. However, we did make some progress. We took our mousetrap and drilled two holes on each end, so we could insert screw holders. These will be used to attach an axle to the mousetrap. One of our main challenges was to find a way to keep the axle from sliding back and forth, because we knew this would decrease the speed we would be able to achieve. Sliding back and forth would create unnecessary friction, resulting in a loss of energy. To stop this we applied duct tape near the screw holders that prevented the axle from sliding, but at the same time did not hinder the spinning of it. We then tested the power that we could generate with our trap attached to the axle. We tinkered with many different ways of attaching a string to the mousetrap and the axle. Should we just wrap it, tape it then wrap it, secure it near the wheels or in the middle of the axle? Finally we came to the conclusion that taping then wrapping it in the middle of the axle would be the best choice. Then we let the trap go to see how many rotations we could get. It turns out that the mousetrap actually generates enough power to possibly do what we are trying to without adding a lever-arm, which is to have the fastest time in five meters. However, we still plan on adding a lever-arm, due to the fact that the more power the better. We are trying to blow the competition away! Next construction day we plan on attaching the wheels and the base.

Mousetrap Car with Paul

Paul and I came up with the concept for our mousetrap car after watching many videos on youtube. Many people claimed to have the best mousetrap cars, but we used our knowledge of physics to help us figure out which one we thought we needed to use. The part that was the deciding factor was actually what type of wheels the cars used. Some had holes in them, some were big, and some were small. Knowing what we know about rotational inertia, we knew we had to use a solid wheel.

The wheels will have rubber bands wrapped around them in order to achieve more friction, so that they will grip the floor. Which means that when the mouse trap gets the wheels rotating they won't do any excess spinning without moving. One of our main points of emphasis was to make everything as simple as possible, so that we could reduce the amount of error possible. We are planning on using the normal lever-arm of the mousetrap. Also we are going to use smaller wheels on the front of the car to reduce the mass and create less rotational inertia. Since this race is about speed and not distance, we must be able to achieve as much acceleration as possible, which is why we are using things like the rubber bands and smaller wheels

Materials
Materials provided by Mrs. Lawrence
Rubber Bands -- Goes on the wheels
Paint Sticks -- Used to put wheels on
Kebab Stick -- Axis of the car

Unit 5 Blog Reflection

Unit 5 was all about rotational motion. We covered concepts from tangential speed to conservation of angular momentum. Thats a lot of information, but I'm going to do my best to explain it all. Let's start off with tangential speed, which is the linear speed tangent to a curved path. The "v" in this image shows tangential velocity. Tangential speed ~ radial distance x rotational speed.

Tangential speed is related to something called, rotational speed. Which is the number of rotations or revolutions per unit of time. A real life example, is a merry-go-round. Pretend there is one kid sitting very close to the center, then there is another sitting on the edge. They both are moving with the same rotational speed, because they are sitting on the same object that is making a certain amount of rotations per unit of time. However, the kid sitting near the edge of the merry-go-round has a faster tangential speed, due to the fact that he is further away from the center, thus his radial distance is greater.That leads me into my next topic off rotational inertia. Which is that property of an object that measures its resistance to any change in its state of rotation: if at rest, the body tends to remain at rest; if rotating, it tends to remain rotating and will tend to do so unless acted upon by an external torque. An example of rotational inertia is a circus tightrope walker. Most of the mass of the pole is located away form the axis of rotation, giving it more rotational inertia. If the tightrope walker begins to fall over the pole will resist this change in rotation, giving the walker more time to correct themselves. The longer the pole the better.

  

In the definition of rotational inertia, I used something called torque. The product of force and lever-arm distance, which tends to produce rotation. 

TORQUE=LEVER-ARMXFORCE

You can have counter and counter clockwise torques, which when equal cause an object to be balanced.

Next we have center of mass and center of gravity. Center of mass is the average postition of the mass of an object. The CM moves as if all the external forces acted at this point. CG id the average postion of weight or the single pooin associated with an object where the force of gravity can be considered to act. If ones center of mass is not within his bass, this will cause that person to lose there balance and fall. This relates back to counter and clockwise torques which must be equal to have balance as I stated earlier. There is two new forces we learned about as well, and they are centripetal force and centrifugal force (doesn't actually exist). Centripetal force is directed towards a fixed point and cause rotation by pulling an object inward. For example if you have a ball on the end of a string and you spin it above your head you are creating centripetal force. Centrifugal force is the outward force you or an object experiences when rotating. When you turn in a car, your body hits the door, this is "centrifugal force" even though there's not even any force acting on you. Centrifugal force is an imaginary force. Angular momentum is the product of a body's inertial and rotational velocity about a particular axis. One thing that must be remembered is that angular momentum is conserved. The formula for angular momentum is ROTATIONAL INERTIA X ROTATIONAL VELOCITY. The concepts in this unit were not very difficult, however there were a lot of new concepts to learn. One thing that was hard to understand at first was the tangential speed and rotational speed and when they remain the same. All of these concepts relate to real life, from on the playground to when you are driving in a car.