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. 

Finding the Mass of a Meter Stick without using a Scale

In order to find the mass of the meter stick without using a scale, I was forced to use my knowledge of physics in order to come up with an answer. First, I figured that I had to balance the meter stick on the edge of the table in order to find its center of mass. Which means that on either side of the center of mass the torques are equal. Then I had to place the weight on one end, which had a mass of 100 grams, and adjust the meter stick to once again find the center of mass. Since I could look on the meter stick and see how long each lever-arm was and i knew the force being applied to the one side I could set up this equation, lever-arm x force = lever-arm x force. I know I can do this because the torques are equal. After I came up with an idea of how to do this I put my thoughts into action. In Step 2 I began by finding the center of mass of the meter stick by balancing it on the edge of the table. The center of mass was at 50.5 cm. Then I placed the 100 gram weight on one side, and then adjusted the meter stick in order to find the new center of mass, which was at 70 cm. The first time I did this process I made a simple mistake. When finding the distance of the lever-arm with the weight, I counted from the center of mass to the end of the stick on the long side. However, all I needed to do was go from the new center of mass to the old center of mass. Which would make the lever-arm of the unweighted side 20 cm instead of 70 cm. This made a huge difference in my calculations. So, after I figured out my mistake the equation looked like (20xforce=30x9.8). The 20 comes from the process I explained above, and the 30 comes from the second center of mass to the end of the stick (weighted side), these are the two lever-arms for the equation. Finally, I got the 9.8 by finding the weight of the 100 gram weight by using the equation w=mg, and this is the force for the weighted side so all that is left to do is find the force on the unweighted side and convert it back to grams. After I completed all of the calculations, I found that the weight of the meter stick to be 150 grams. The actual weight was 149.3, so I was only 0.7 grams off.

Unit 4 Blog Reflection

      In Unit 4, we learned about momentum. This unit was one of the more useful units, because I felt as though it completely related to real life. The equation for momentum is p=mass x velocity. An object will have a large momentum if its mass or velocity is large, or if they both are. Here's a useful video to help get a better understanding of momentum. Of course you can't expect the momentum of an object to always remain constant. It is going to change, and this change in momentum is called impulse. There are a couple of vital equations when dealing with impulse. They are, impulse (J) = force x change in time, and J= change in momentum (p).  To increase the impulse, you must either increase the force, time, or both. However, when the impulse is constant, force and time on he equation are inversely proportional. Meaning that when you increase one the other decreases. There is one law that applies to momentum and it is the law of conservation of momentum. It states that the only way to change the momentum of an object is to exert an external force on it. No net force or net impulse equals no change in momentum. The official way to say this is that in the absence of an external force, the momentum of a system remains unchanged. As far as impulse goes, one thing to note is that the impulse of a bouncing is greater, because not only must the object be brought to a stop, but it must also be thrown back again. Here's a helpful video to help you get a better understanding.

Next up is collisions, which are actually pretty interesting. As we already know momentum is conserved in collisions (The net momentum before= the net momentum after). There are two types of collisions, which are elastic (two objects bounce of one another) and inelastic (two objects stick together). We can figure out the momentum that colliding objects have by using the first equation in elastic collision and the second in inelastic collisions.

(Remember m=mass and v=velocity; also m1, ma, m2, mb, v1,v2,va, and vb are all before the collision.)

Lastly, we have complex collisions, which involve to objects in different directions crashing together.
They create a combined momentum in a combined direction in inelastic collisions. A pool ball is a good example of a complex elastic collision. The cue ball hits the 8 ball at an angle and they both travel in different directions. However, in complex collisions momentum is still conserved.
      This unit provided some difficulties when it cam to the lab problem. I had a hard time figuring out how to manipulate the equation in order to get the slope. But, it taught me a very valuable problem solving skill. It showed me that in order for scientists to prove their data sometimes you must manipulate the equation y=mx+b. This unit relates to real life situations, because it can help you learn how to minimize injury in crashes by increasing the time with things such as pads or airbags, in order to lower the force
GO PHYSICS!

Unit 3 Summary

In Unit 3 we learned about three major concepts. They are Newton's Third Law, Universal Gravitational Force, and tides. Throughout this unit my logic was challenged and things that I previously viewed as easy to understand were proved far more complex than I thought. First off I will start with describing Newton’s Third Law and how it is present everywhere in the real world. This law states that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. So, this creates action-reaction pairs, which can be written as simple as, Dorian pushes on wall and wall pushes on Dorian. Anytime an object exerts force on another object, the other object will exert the same amount of force. Before unit 3, I believed that in order to win a game of tug-of-war one side must pull harder than the other. However, this is not true because no matter how hard one-team pulls the other team will pull with the same amount of force (Newton’s Third Law). To win a game of tug-of-war one team must use the ground as an outside force, so the team who pushes on the ground harder will win. Next up is The Universal Law of Gravity, which states that everything pulls on everything else in a way that involves only mass and distance. This law can be written as F=Gmass1xmass2/distance squared. The G in the equation is the universal gravitational constant, which equals 6.67x10 to the power of 11. When you double the distance you decrease the force by the one fourth, which is called the inverse squared law. The equation always follows this pattern. When someone thinks of tides they usually think that tides are caused by the moon’s force on the Earth. This is partly true, but the actual cause of tides is the difference in force on each side of the Earth. This is caused by the difference in distances form the moon that each side of the earth has. Thus, creating a tidal bulge that has a high tide on opposite sides and low tide on opposite sides.  In this diagram A and C are experiencing high tides and the other sides are experiencing low tides. Also, the vector arrows show the difference in force from side C to side A.

  

 There are two specific types of tides that we learned about. The first is spring tides, which occur when the moon, earth, and sun are aligned creating a full or new moon. At this time the high tides are higher than usual and the low tides are lower than usual. The next is neap tides, which occur when the sun is at a ninety-degree angle to the earth, creating lower than usual high tides and higher than usual low tides.

          It is very difficult, at first to fully understand the fact that no matter how hard you push on an object that object will push back on you with the same amount of force. This totally goes against what I perceived as logical. This unit actually helped me improve my math skills, because while using the Universal Gravitational Law. Not being able to use a calculator taught me how to solve equations with exponents in a much simpler way than I had previously been doing. With the knowledge I have gained from this unit, I will be able to go to the beach and try to predict what tide is about to happen and whether it will be higher or lower than usual.

Unit 2 Blog Reflection

Unit 2 was a unit that presented may contradictions to the way i previously viewed falling objects and projectiles. The main overlying theme of this unit is Newton's Second Law, which is acceleration=net force/mass. The unit started of talking about free falling objects, or objects falling by the force of gravity alone with no air resistance. It is important to remember that a free falling object must start from rest and when an object is in free fall the force of gravity (which is 10 or 9.8 to be more specific) is its acceleration. Two equations can be associated with free fall and they are the distance or how far equation (distance=(1/2)gravityxtime squared) and the velocity or how fast equation (velocity=gravityxtime).  Next we moved on to objects falling with are resistance. These objects have to things they must take into account, the force of the air and the force on the falling object. Instead of always being a constant acceleration, like in free fall the accelerations vary. We can find the acceleration by using the formula acceleration=Fweight - Fair/mass. Also, there is something called terminal velocity, where the Fweight and Fair are equal, the velocity stays constant, and there is no acceleration. So what happens when you throw an object upward? It must come down right? So we use the same equations we have for free falling objects to help us calculate the distance and velocity of the object as it rises. Remember that on this case the acceleration of the object will be negative ten meters per second squared. Lastly, we learned about projectiles, which is basically an object being launched at an angle. We must take into account the vertical and horizontal velocity in this situation, so the velocity of the object will never reach zero (unless it hits the ground). Horizontal velocity remains constant, while vertical velocity uses the sam principles as a free falling object, so the same equations can be applied. One thing that was difficult for me to understand is how to find the distance an object that has been thrown up travels. Because, I knew you could not use the distance formula due to the fact that it did not begin at rest. Eventually, I was able to grasp the concept that an object going up must come down and when it falls down it starts from rest. So, you must calculate that distance and it will be equal to the distance the object traveled up. Some of the projectile problems require a lot of problem solving skills. With the horizontal and vertical velocities, it makes it possible to apply pathagorean's theory. However, I believe I did very well in my problem solving and seemed to always come up with an answer at least.  Everytime you drop something or something falls off of your desk these principles are being used and since I have a better understanding of them I know exactly what's going on. Also, when you shoot a basketball it is a projectile. Maybe, I can calculate the proper velocity and distance to shoot it with in order to make the shot everytime.