Types of energy

1.       Gravitational potential energy: Gravitational potential energy is energy an object possesses because of its position in a gravitational field. The most common use of gravitational potential energy is for an object near the surface of the Earth where the gravitational acceleration can be assumed to be constant at about 9.8 m/s2. Since the zero of gravitational potential energy can be chosen at any point (like the choice of the zero of a coordinate system), the potential energy at a height h above that point is equal to the work which would be required to lift the object to that height with no net change in kinetic energy. Since the force required to lift it is equal to its weight, it follows that the gravitational potential energy is equal to its weight times the height to which it is lifted.

2.       Chemical energy: it is a form of potential energy. chemical energy is the energy involved in the bond formed between two atoms. Each bond within a chemical compounds involves different amounts of energy. When one of these bonds breaks,  a chemical reaction occurs and chemical energy is used. The bond is released and is either reused in forming new bonds with other atoms or enters the surrounding atmosphere as heat. You can’t see chemical energy or touch it, but you can see it released when reactions occur.

3.       Mechanical kinetic energy: The kinetic energy of an object is the energy which it possesses due to its motion.[1] It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The same amount of work is done by the body in decelerating from its current speed to a state of rest.

4.       Thermal energy: A specialized term that refers to the part of the internal energy of a system which is the total present kinetic energy resulting from the random movements of atoms and molecules. The ultimate source of thermal energy available to mankind is the sun, the huge thermo-nuclear furnace that supplies the earth with the heat and light that are essential to life.

5.       Sound energy: Sound energy is the energy produced by sound vibrations as they travel through a specific medium. Sound vibrations cause waves of pressure which lead to some level of compression and rarefaction in the mediums through which the sound waves travel. Sound energy is, therefore, a form of kinetic energy; it is not contained in discrete particles and is not related to any chemical change, but is purely related to the pressure its vibrations cause.

6.       Elastic potential energy: Elastic potential energy is Potential energy stored as a result of deformation of an elastic object, such as the stretching of a spring. It is equal to the work done to stretch the spring, which depends upon the spring constant k as well as the distance stretched. According to Hooke's law, the force required to stretch the spring will be directly proportional to the amount of stretch.

Canon

Our new class assignment is to build an ethanol fueled canon. the challenge is to build a cannon that has the longest range. Before actually build it we have to first design it in order to achieve a longer range. In order to achieve that goal, some background research was needed. It was very hard to find background information about cannon because almost all the searching results are about the brand called Canon, but I was still able to pull something out.

According to research, there are basically two factors that can affect the range of the ethanol fueled cannon. The first factor is the angle of the barrel. Angle is a very important factor to maximize the range. Consider this, the energy given is about the same which is 3ml of ethanol, and we already know from projectile motion that gravitational force is the reason why cannon ball will fall. Therefore, if we threw a ball too high, the v_y factor will have a bigger value, therefore the maximum height may be very high, but the vx will be smaller because the energy is taken by vy. And if we threw a ball too low, the vx factor will be bigger but since the vy is smaller, the ball will land on the floor very soon. Therefore, 45°is the angle that can have the maximum range because all vectors are equal.

The second factor that can affect the range is the height of the cannon. As I mentioned above, angles that are below 45 degree have a bigger vx component, but due to the insufficient of vy, the ball will land on the floor very fast. But if the height of the cannon was increased, the vy component will increase too. Therefore, the ball will have a longer hang time and this will maximize the range.

4 types of Newton problems

Projectile motion

Physics behind roller coasters

Everyone should at least ride on a roller coaster once before he dies, to experience the excitements physics bring. You may question, why do I say physics? Aren’t the roller coasters driven by electricity? In fact, it is driven only using potential energy and kinetic energy.

Potential energy is the energy stored in an object or in a system due to its position in a force field or due to its configuration. For example, a text book will create a very laud sound when it is dropped on the floor. Where does that sound energy come from? Well, gravity gives energy to all objects on this planet, the higher the text book is from the ground, this greater the energy it is stored. Therefore, gravity is the driven force of the roller coaster. When the train is released from the top of the lift hill, gravity pulls it down. Potential energy is the greatest when it is at the highest point of the roller coaster, as is the lowest at the lowest point. Kinetic energy is the energy which it possesses due to its motion. As it slides downwards, the potential energy is converted into kinetic energy, because according to Einstein’s conservation of mass, energy cannot be created or destroyed, but it can be converted from one form to another. However, every roller coaster system will have friction force between the wheels and the rail, which is one of the major factors that cause the coaster to slow down.

How to add vectors

How to add vectors?

1.       Set positive axis (north east)

2.       Break vectors into x components and y components

3.       Calculate x and y by sin and cos

4.       Use Pythagorean theory to solve for R (a2 + b2 = c2)

5.       Use tan to solve the angle of R

deriving equation 3 and 4 from graph

The motion lab: translating walking graph

A: the object stands 1m away from the origin for 1 second

B: the object moves away 1.5m from the origin for 2 seconds

C: the object stopped moving for 3 seconds

D: the object moves 0.75m towards the origin

E: the object stands 1.75m away from the origin for 2.5 seconds

A: the object stands at 3m and moving towards the origin 1.5m for 3 seconds

B: the object stopped moving for 1 second

C: the object moves 1m towards the origin for 1 second

D: the object stopped moving for 2 seconds

E: the object moves 2.5m away from the origin

A: the object stays at the origin for 2 seconds

B: the object walks away from the origin at a velocity of 0.5m/s for 3 seconds

C: the object stays for 2 seconds

D: the object walks towards the origin at a velocity of 0.5m/s for 3 seconds

A: the object speeds up for 4 seconds

B: the object moves away from the origin at a velocity of 0.5m/s for 2 seconds

C: the object moves towards the origin at a velocity of 0.4m/s for 3 seconds

D: the object stays for 1 second

 

A: the object moves 1m away from the origin for 3.5 seconds

B: the object stays for 3 seconds

C: the object moves 1.3m away from the origin for 3 seconds

A: the object moves away from the origin at a velocity of 0.3m/s for 3 seconds

B: the object speeds up for 0.3 seconds

C: the object slows down for 0.3 seconds

D: the object moves towards the origin at a velocity of 0.3m/s

E: the object stays for 3 seconds

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