Building our own motor

         Today we built a motor in class with a partner. I was partnered up with Jessica and we had a lot of fun together.

         Our mission is to build a motor that could rotate at least three rounds. We brought our own materials to class, such as woods, corks, nails and pop cans. Our wood is not wide enough, so we nailed two pieces of narrow wood sticks together to form a wide one. We had 30 minutes to finish all the nailing work because it was very noisy and we were interrupting other classes. I thought Mr. Chung gave us too much time on this, but I was wrong. When he said that time is up and we have to return the hammers our group far from finish, so we actually kept a hammer secretly in order to finish the work. And the reason why we are running out of time is because we had to do many measurements and fittings. However, I and Jessica had a great team work though, when I was doing the nail work, she was sanding the pop can and the stripes of the wire at the same time. Therefore after the nailing part, everything went so quick and smooth. We soon combined all the parts together and tested our motor. Yeah! We passed the first time! I was amazed by our success and by seeing a real motor spinning so fast. So I guess our biggest obstacle will be the nailing part. It really took us almost the whole period.

         Then Mr. Chung said that we need to blog about our motor today. So I take out my cell phone and ask Mr. Chung to retest for us so that I can record it and upload it to my blog. But the thing is, our motor is not working anymore! Mr. Chung said: “thank god you’ve passed. Go back and fix it.” So I tried to fix it but I only made it worse. The second time I tried to test it, there was only sparks between the brush and the commutator. Finally Mr. Chung found the problem and fixed it. It was because we used a really bad commutator .

         Sorry that I don’t have any picture or video of our motor. I couldn’t find my usb cable for my cell phone, but I will try to upload some pictures tomorrow.

Notes from pg582-589

17.1 The magnetic force

1.       Magnetic field – the distribution of a magnetic force in the region of a magnet. There are two magnetic characteristics, labeled north and south, that are responsible for magnetic forces. Similar poles repel one another, dissimilar poles attract one another.

2.       Earth is like a giant permanent magnet, producing its own magnetic field. It is suggested that earth’s magnetic field is produced because of the flow of hot liquid metals inside earth.

3.       Magnet forces don’t act just between two magnets; they also attract certain metals such as iron, nickel and cobalt. These metals are called ferromagnetic metals. All magnets are made up of these metals.

4.       Domain theory: all large magnets are made up of many smaller and rotatable magnets, called dipoles, which can interact with other dipoles close by. If dipoles line up, then a small magnetic domain is produced.

17.2 Electromagnets

5.       Oersted’s principle: charge moving through a conductor produces a circular magnetic field around the conductor.

6.       Right hand rules are developed to help you predict how magnetic forces act.

7.       Right hand rule #1 (for conventional current flow): grasp the conductor with the thumb of the right hand pointing in the direction of conventional current flow. The curved fingers point in the direction of the magnetic field around the conductor.

8.       Right hand rule #2 (for conventional current flow): gasp the coiled conductor with the right hand such that curved fingers point in the direction of conventional (positive) current flow. The thumb points in the direction of the magnetic field within the coil. The thumb represents the north of the electromagnet.

9.       Factors that determine the strength of an electromagnet:

1.       Current in the coil

2.       Number of turns in the coil

3.       Type of material in the coil’s centre

4.       Size of coil

10.   Left hand rule works the same way as right hand rule, the only difference is that left hand rule is the rule of the flow of charge(- to +), and the rule uses the left hand to complete.

Notes from pg553-563

1. The amount of energy transferred depends on:

1. The potential difference of the power supply (amount of push)

2. The nature of the pathway through the loads that are using the electric potential energy.

2. Resistance - A measure of the opposition to the current flow in a circuit.

3. Ohm’s law:

         R = resistance (Ω), a measure of the opposition to the current flow in a circuit

         I = current (A), flow of charge

         V = voltage (V), electrical potential difference

4. Current has direct relationship with voltage in the resistor as long as other variables such as temperature are controlled.

5. Factors that determine resistance:

         1. Length, material ↑, resistance ↑

         2. cross- section area, cross-section area ↑, resistance ↓

         3. Material it is made of

         4. Temperature, temperature ↑, resistance↑

6. Series circuit – the loads are connected one after another in a single path, if one point of the circuit breaks, the whole circuit breaks too.

7. Parallel circuit – the loads are connected side by side, if one point breaks, the current can still go through other points, the whole circuit will not break.

8. Kirchhoff’s law: the total amount of current into a junction point of a circuit equals the total current that flows out of that same junction.

         IT = I1+I2+I3+I4+I5

9. Kirchhoff’s voltage law: the total of all electrical potential decreases in any complete circuit loop is equal to any potential increases in that circuit loop.

         VT = V1+V2+V3+V4+V5

10. Laws of conservation of electric charge and the conservation of energy: in any circuit, there is no net gain or loss of electric charge or energy.

Ohm's law prelab chart

Circuit qustions#1-12

1. Can you make the energy ball work? What do you think makes the ball flash and hum?


Yes, I can make the energy ball work. I think we are good conductors and static electricity container. By touching both metal contacts, I am actually forming a closed circuit. And I think the battery is inside the ball, once the two metal contacts are connected by a conductor, the ball will flash and hum.

2. Why do you have to touch both metal contacts to make the ball work?

The two metal contacts are necessary to form a closed circuit, because the electric current is travelling from positive to negative. Therefore, 2 metal contacts are needed to complete this action.

3. Will the ball light up if you connect the contacts with any material?

No, the ball wouldn’t light up if I connect it with any materials, because not all materials are conductors.

4. Which materials will make the energy ball work? Test your hypothesis.

I think metal will make the energy ball work. I used my silver necklace to test my hypothesis and it did work.

5. This ball does not work on certain individual, what could cause this to happen?

Perhaps that certain individual is not using his or her bare skin to connect to the metal contacts, or perhaps his or her body doesn’t have electrolyte or water.

6. Can you make the energy ball work with all 5-6 individuals in your group? Will it work with the entire class?

Yes and our class had tested it.

7. What kind of a circuit can you form with 1 energy ball?

Simple circuit would form with one energy ball.

8. Given 2 balls (combine 2 groups): can you create a circuit where both balls light up?

Yes, we formed a series circuit in order to light both balls up.

9. What do you think will happen if one person let go of the other person’s hand and why?

I think if one person let go of the other person’s hand, the whole circuit will break, and the two balls will stop flashing.

10. Does it matter who let’s go?

No, it doesn’t matter, because in a series circuit, no matter which part is broken, the whole circuit is broken.

11. Can you create a circuit where only 1 ball lights? Both must be included in the circuit.

Yes, by creating a parallel circuit.

12. What is the minimum number of people required to complete this?

I think the minimum number of people required to complete a parallel circuit is 2 people.

The physics challenge

The physics of tall structures:

When our group was building the paper structure, we took a long period of time to discuss the factors that could affect the height. We reached a consensus that a strong base would hold up a stable and tall building. Therefore we decided to build a pyramid shaped base because pyramid can equally disperse the pressure and it has a very firm structure. In addition, pyramid is heavy at the bottom and light on the top, which is another important physics principle when building tall structures. We also thought about the strength of the news paper. It is too weak to support each other. So we rolled the news paper into a solid stick, we thought this stick would have the strength to support the whole structure. But in the end, we were wrong about it because it collapsed. According to Mr. Chung, the reason why we couldn’t succeed is because the paper sticks we made are too heavy, and it is not thick enough in order to balance. We learned so many physics in just one activity, such as the mass of the structure is also very important.



What makes it stable:

Even though our structure collapsed in the end, I still discovered some factors from our failure experiment that could make it stable. For example, a tall structure always has a large and heavy base to support the rest of the mass on the top, this way the structure will be balanced and stable.



What is the centre of gravity:

In physics, all parts of an object are affected by gravity, the point where the gravity of each part concentrate is the centre of gravity. The location of the centre of gravity depends on the objects shape and mass distribution inside the body. In a mass equally distributed object, the centre of gravity will be at the centre of the geometry figure. For example, the centre of gravity of a balanced sphere is in the centre of the sphere. In a mass not equally distributed object, the centre of gravity will be depending on the location of mass. For example, the centre of gravity of a track is depending on how much goods are carried or which part of the truck carries goods.

centre of gravity in a mass equally distributed object

centre of gravity in a mass unequally distributed object

Notes on current electricity

1. Electric current is the rate of charge flow. The symbol is I.

2. Current equation: I = Q ÷ t
I=the current in ampere
Q=the total amount of charge moving past a point in a conductor (coulombs)
T=the time taken (second)

3. The base unit of current is C/s, this Is called ampere

4. Electrical energy always originates from other energies, it can change these easily produced forms to the form we need.

5. Common sources of electrical energy: chemical, mechanical, thermal, or light energy.

6. The conductor carries energy is the same with pipes carry water.

7. Electric circuit is a closed loop which an electric current exists or is intended or able to flow.

8. According to Ampere’s law, an electric current produces a magnetic field.

9. This is a picture of a electric circuit. Electron current flow along the circuit wire from the negatively charged terminal toward the positive terminal, opposite to the direction of the conventional current.

10. Common conductors: copper, silver, aluminum