Electrostatics Lab

8.1.1 Electroscopes
1. Yes. As we rub the rod harder, it will gain more electron and be negatively charged, causing the vanes separate further due to the amount of the electrons.
2. When the negatively charged rod is pulled back without touching the electroscope (induction), the positively charged electroscope will move to the vanes, which is negatively charged now. This will bring the vanes closer together.
3. They produce the same effect because when the positively charged rod is brought closer to the electroscope, the electroscope now will be negatively charged, leaving the vanes positively charged, thus the vanes repel.
4. Because the electroscope has obtained negative charges from the rod through conduction process. The electroscope is still negatively charged when the rod had been removed.

8.1.4 Induction

1. The glass will be positively charged after it had been rubbed with silk. The positive charged in the paper are repelled downwards. The upper side of the paper becomes negatively charged and is therefore attracted toward the positive glass.
2. Because when the paper acquires charges from the glass by conduction, it will be repelled due to similar charges with the glass.
3. The bob will first be attracted by the charged plastic rod by induction, then it acquired a similar charged by conduction, then will be repelled due to similar charges. Now the bob is negatively charged. When the charged bob contact with the uncharged glass rod, the glass rob acquires charges from the bob as thus be same charged. The bob therefore will be repelled by two rods, causing it to bounce back and forth between the two rods.
4. The Cheerios will be charged by conduction when the Vande Graaf generator is turned on. Then the Cheerios fly up because of the repulsion of like charges.
5. This could be explained that the hair on my arm will be attracted by the negatively charged electrons in the cloud, which is much more when the lightning is about to strike.

8.1.5 Distribution of Charge

1. The tiny blue beam at the end of the metal rod indicates the transfer of the electrons from the dome to the rod.
2. The lightning rod is an excellent conductor that allows the current to flow to ground without causing any damage.

8.1.6 Electrostatic Separators

1. Adding water to the mixture of salt and pepper, mixing it until salt is dissolved. Once salt has dissolved in water use filter paper and funnel to filter the pepper out of the salt and water. (Chemistry)
3. Those areas not covered by paper are charged and therefore attract pepper.

8.1.7 Electric Potential

1. An electric field strikes the fluorescent material that lines the lamp interior and causes it to glow.
2. Because the electric field is operated perpendicular to the surface of the object. Thus the tube does not glow brightly when positioned tangential to the surface of the dome. 

Supercard Challenge #1

Attraction and Repulsion of Neutral Obj

Attraction and Repulsion of Neutral Objects

Well, my initial thought would be that a positively charged object can not attract or repel a neutral charged object. Nothing would happen. But this assumption was proved wrong when the Teflon rod was rubbed by the bunny, it was positively charged. And as I brought the rod closer to the paper, which is neutral, it attracted the paper. This kind of attraction can be explained by induction. As the positive object is brought closer to the neutral object, charge separation occurs within the neutral object, resulting an electric dipole moment. The positive and negative charges will be rearranged so that positive charges come to one side and negative charges are brought toward the charged one. Thus, the object becomes attracted. 

Projectiles Force

To calculate the force acting on the trebuchet, one must know the initial velocity which launches the ball and the angle at which the ball is launched. Also, the law of conservation of energy (kinetic and potential) is involved in this calculation.

Projectiles - Write Up

http://www.youtube.com/watch?v=7xO-TCB0t70

1.       What was your original construction idea?

Our original idea is doing a small trebuchet that have enough force to launch the tennis ball. This trebuchet requires human power to launch. 

2.       What challenges did you face in construction?

Measuring the material and assembling those parts are quite exhausting as we have to make sure that everything is fit together . Our final trebuchet is bigger than our original idea, so it requires more effort. 

3.       Did you stick with your original plan?  Why or why not?

We didn't stick to original plan. We thought about how small that was, so we determined to do the big trebuchet that launched the ball further.

4.       Explain how your device works.

We attach the counterweight to the short arm. It is about 40 lbs. We also use the string as device to launch the projectile. The ball will be placed in the basket resting on the base. When we pull the string, it will release the long arm. The counterweight will fall down, launching the ball as the long arm goes up.

5.       Where and how was this device used in history?

It was used extensively in the Middle Ages by the French. Medieval Trebuchets could launch missiles hundreds of yards at, or even over, a castle, fortress or city wall.

6.       What did you learn by constructing this device?

We learn how to construct and build a device that applying physics' theory. 

7.       What principals of physics did you utilize in this device?

We use the law of gravitational potential energy to build the trebuchet. We also apply  Conservation of Energy law. 

8.       Tell about a career where this type of device could be useful.
These trebuchet can be used in the military. Those office in military might use trebuchet to throw dead bodies or destroy castles ( which I don't usually see). Physics teacher or students major in Physics can learn how to build trebuchet to understand more about the law of physics.

9.       Could this type of device be useful in getting people to space?  Why or why not?

The escape velocity is approximately 25,053 mph. This velocity is required for the device to escape the earth and go to space. It is nearly impossible to use trebuchet for this purpose. 

Projectiles - Test Fires

We didn't do well on the accuracy test. The angle of the releasing pin on the swing arm was not consistent. We must change the angle of the pin each time of the test. The accuracy distance, therefore, was affected by the pin.

Projectiles - Safety Concerns

Safety is the most important thing to be considered when building the trebuchet. Any loose parts must be tightened. The trebuchet must be stable when firing or it will cause danger. The weight attached to the short level arms must be firm. When firing, no one should be standing near the front and the end of the projectile. Everybody should be away 2m from the projectiles and wearing goggles.

Rube Goldberg - Final Submission

Here is our final lab: https://www.youtube.com/watch?v=_w5GLvRXEwE

 Most energy is lost as Eliza letting the marble slide down. As the marble slides down, its potential energy is being converted into kinetic energy. The total energy is always conserved. I will pick the first energy change, which is potential energy to kinetic energy, to perform my calculation. In order to know how much energy changes during this section, first I need to know at what height the marble is rolling down. Height and the mass of the marble are also taken into consideration. For this, I will determine the final energy at the end of the first energy change. The change in kinetic energy indicates the work of the marble. Its power can be calculated using its force and velocity; the product of these two components will give me the power of the marble. Total energy is very much simple since it is either the initial potential energy or the final kinetic energy.

This lab is a good experience for me as I learn a lot through it. Working with other students sometimes pisses me off, but as we comes together and agree on our ideas it is pretty easy to overcome the task. This assignment gives me a good knowledge of what I would be doing in college. I hope we can have few more of this the rest of the year.