different types of energy

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.


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.


Mechanical potential energy
-  mechanical energy is the sum of energy in a mechanical system. This energy includes both kinetic energy, the energy of motion, and potential energy, the stored energy of position. A mechanical system is any group of objects that interact based on basic mechanical principles.


Chemical potential energy
-   Chemical potential energy is a form of potential energy related to the structural arrangement of atoms or molecules. This arrangement may be the result of chemical bonds within a molecule or otherwise. Chemical energy of a chemical substance can be transformed to other forms of energy by a chemical reaction.


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.


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.

cannon!

yeah!! we'll be building our cannons on Thusday!! the cannon is made of 5 pop cans. according to last unit(projectile motion), we know that the best angle to set our cannons is 45°、because it would reach the farthest distance.
But of course, the real cannon is not made of pop cans..
A cannon is any piece of artillery that uses gunpowder or other usually explosive-based propellants to launch a projectile.

Newton!!!

For equilibrium:
assumptions:

-          no air resistance

-          no friction

-          a=0 ( ax=0 and ay=0 )

-          break down in to x and y components

-          T1x=T2x

-          set positive axis⊕

for inclined problems：

assumptions：

-          no air resistance

-          FN  perpendicular to the surface

-         ＋axis is the direction of the motion

-          break down in to x and y components

-          acceleration does not equal to zero

-          FN-Fgy=0

-          Fgx-f=ma

 

for pulley problems:

assumptions:

-          pulley is frictionless

-          rope is frictionless

-          no air resistance

-          + axis is the position of the

-          2 Free Body Diagrams

-          T1=T2

-          ay1 = ay2

-          break down in to x and y components acceleration

 

for train prblems,

we consider the trains as a whole, to solve for ax.

Assumptions:

- 3 FBD to find T

- no air resistance

- ay = 0

- cables weightless

- positive along acceleration

- acceleration is consistent

projectile motion

when we do projectile motion problems, we always break the motion into to components. x component and y component. for x component, the acceleration is always zero, in other words, no acceleration for x. for y component, the acceleration is the same as gravity which is 9.8m/s
 

there are 4 types of projectile motion:
-the first one is when someone throw something from the higher level to the horizon.



-the second one is someone throw something from the horizon to the horizon.


-the third one is someone throw something from the horizon to the higher level.

-the last one is someone throw something from the horizon to the lower level.

physics behind roller coaster

Gravity is an important component of a roller coaster, the gravity pulls the roller coaster down to the ground, so that so roller coaster won't move vertically forward.
For a non-idealized roller coaster system, not all of the energy is conserved.  Friction is the main cause of energy leaks in the system and the reason why mechanical energy is not fully conserved for a real roller coaster.  This is because friction is a nonconservative force.  Nonconservative forces are forces that cause a change in total mechanical energy.  Friction opposes motion by working in the opposite direction.  The friction between the train and its tracks as well as between the train and the air take energy out of the system, slowing the train and creating both heat and sound.  This effect is most noticeable at the end of the ride as all remaining kinetic energy is taken out of the system though brakes.  Because of the energy leaks due to friction, each successive hill or loop on a roller coaster must be shorter than all the hills or loops previous to it, otherwise the train will not have enough energy to make it all the way over.

vector addition

     When we are doing vector additon question, we basically just add the X and Y. For each vector, we calculate the X and Y by doing the math, we use sine or cosine to calculate the value for "x" and the value for "y". And we add all the X together, also, add all the Y together, to obtain the final result Dx and Dy. Once we get that value, we can simply get the final result by using the pythagorean theory, and then use tangent law to calculate the angle.
And That is the Final Answer /!!!

equation 4

equation 3

the motion lab---walking graphs

Graph 1:

start at 1 meter away from the sensor and rest for 1 second, and then speed up, walk in positive direction  constant speed for 2 seconds. and then stop for  3 seconds, and then walk in negative direction constant speed for 1.5 seconds, and the graph is done.

Graph 2:

start 3 meters away from the sensor and walk in negative direction constant speed for 3 seconds, and then rest for 1 second and continue walk in negative direction constant speed for 1 second and then rest for 2 seconds and then walk in positive direction constant speed.

Graph 3:

Walk constant speed, run, keep the same speed, slow down and walk constant speed, walk very slowly and walk constant speed.

Graph 4:

 speed up for 4 seconds away from the origion, and then walking for 2 seconds at 0.5m/s away from the origion. slowing down for 0.15 seconds then stopping. then speed up for 0.15s towards the origion. and then walking for 3 seconds at 0.375m/s towards the origion. speed up for 0.1s towards the origion. rest for 0.9s.

Graph 5:

Starts at almost 1 meter from the origion and walk to the positive direction constant speed 1meter for 3 and half seconds, and then rest for 3 seconds and then walk fast to the positive direction in constant speed. 

Graph 6:

Walk at the constant speed for 3 sec at 0.375m. slow down and keep the same speed for 3 seconds, and little bit faster and keep the same speed.



the motor

     Our task for “Building an electric motor” this project was to build an electric motor and make the commutator spin. This simple motor was basically made of materials such as cork, wires, wood, thumbtack nails, and aluminum pieces. Firstly, we hammered the four nails into the wood, the distance between them was 5cm×3cm, and we bent two paper clips and placed each of them at the edges of the nails, the paper clips are used for holding the commutator. Secondly, we started to make our commutator. We firstly made the Axel went though the cork, the commutator involves two pins placed into the centre of the cross-section of the cork, and then we sanded the end of two side of the copper wire and wrapped the wire around one of the commutator pins around the cork until there was only a little bit of the wire left to wrap around the other commutator pin. The next is the brushes; we used two pieces of pop can instead of the metal brushes. We sanded both sides of the pop can pieces to remove its “insulation”, and we placed it between the paper clip holders and the nails. Thirdly we put our commutator upon the paper clip holders, and make sure the pins touch the brushes when it spins. Finally, we put 2 magnets, one on each side, and connect the power supply to make the motor spin.

Right Hand Rule#1&2

Right-Hand Rule #1 (RHR #1)
Right-Hand Rule #1 determines the directions of magnetic force, conventional current and the magnetic field.  Given any two of theses, the third can be found.
 

Using your right-hand: point your index finger in the direction of the charge's velocity, v, (recall conventional current). Point your middle finger in the direction of the magnetic field, B. Your thumb now points in the direction of the magnetic force, Fmagnetic.

Right-Hand Rule #2 (RHR #2)
Right-Hand Rule #2 determines the direction of the magnetic field around a current-carrying wire and vice-versa

Using your right-hand:

Curl your fingers into a half-circle around the wire, they point in the direction of the magnetic field, B
Point your thumb in the direction of the conventional current.

Ten Points For Magnetism

1. Magnetic field--the distribution  of a magnetic force in a region of a magnet.
2. similar magnetic poles, north and north or south and south, repel one another with a force at a distance. Dissimilar poles, north and south, attract one another with a force at a distance.

3. 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.
4. Oersted's Principle Charge moving through a conductor produces a circular magnetic field around the conductor.

5. Right-hand rule #1(RHR#1) for conventional current flow Grasp the conductor with the thumb of the right hand pointing in the direction of conventional, or positive(+), current flow. The curved fingers point in the direction of the magnetic field around the conductor.

6. Left-hand rule #1 for conductors Grasp the conductor with your left hand such that the thumb points in the direction of electron(-) current flow. The curved fingers point in the direction of the circular magnetic field around the conductor.
7. Right-hand rule #2(RHR#2) for conventional current flow Grasp the coiled conductor with the right hand such that curved fingers point in the direction of conventional, or positive(+), current flow. The thumb points in the direction of the magnetic field within the coil. Outside the coil, the thumb represents the north(N) end of the electromagnet produced by the coil.
8. Left-hand rule #2 for coiled conductors Grasp the coiled conductor with the left hand such that the curled fingers point in the direction of the electron（-）current flow through the conductor. The thumb points in the direction of the magnetic field within the coil. Outside the coil, the thumb represents the north(N) end of the electromagnet produced by the coil.
9. The magnetic field strength, B, is measured in units called tesla (T).1T is the magnetic field strength when a 1m long conductor, carrying a current of 1A, crosses a magnetic field at 90°, experiencing a magnetic force of 1N.
  the equation is 1T = 1N/A·m
10. Iron, nickel, and cobalt are ferromagnetic metals.

10 Points From Pg553-563

current flow is dependent on the voltage of the power supply and the 'nature of the pathway through the loads that are using electric potential energy'

R is the resistance in volts/ampere, Ohm（Ω）is the unit of the resistance.

Electrical resistance is the measure of an opposition in the flow.

series circuits connect loads in a single path

parallel circuits connect them parallel to each other.

Kirchhoff's current law: the total amount of current that flows through a junction point is the same as the amount of current that flows out of that same junction .

Kirchhoff's voltage law: the total amount of potential decrease in a circuit loop is equal to the total amount of potential increase in that same loop .

the resistance of a conductor depends on its length, cross-sectional area, the material it is made of, and its temperature.

Thinner wire has a larger resistance than thicker wire.

The gauge number of a wire indicates its cross-sectional area. In other words, a small cross-section has a large gauge number.

Just A Table......

Prelab: Using Voltmeter and Ammeter

Done......

energy ball and the diff between a series and a parallel circuit

On friday at Mr. Chung's class, we played the whole period with a ....ping pong ball= =!

Obviously it's not the one we're usually play with(the one is shown above...), it's actually a ping pong ball with electric circuit inside it, and there were two piecies of metal on the surface of tha ball, when your fingers touch both sides of the metal, the ball will start flashing and humming, so we call it "energy ball"! we were divided into groups of 4, and each group was given a envolop with 12 questions inside.

Q1. Can you make the energy ball work? what do you think makes the ball work?

      Yes, of course- -! The ball is actually an opened circuit, the two piecies of metals is actually act as the opened switch. When our fingers touch both sides of the metals, we actually connect the circuit with our body. So the whole electric circuit is complete and that makes the ball work.

Q2. Why do you have to touch both metal contacts to make the ball work?

      I just answered this question at Q1...we have to touch both metal contacts because we have to complete the circuit. Again the ball is an opened circuit, and us were acting like a conducter, when our fingers touch both metals, we actually make the circuit inside the ball.

Q3. Will the ball light up if you connect the contacts with any material?

      The ball can light up as long as the material is a conductor or some materials sort of metals.

Q4. Which materials will make the energy ball work? Test your hypothesis...

      Any materials as long as it is a good conductor..

Q5. This ball does not work on certain individual - what could cause this to happen?

This ball does not work when the material isn't a good conductor.

Q6. Can you make the energy ball work with all 5-6 individuals in your group? will it work with the entire class?

     Yes, of course//the enery ball lights up in my group by connecting hands. It will surely work with the entire class as long as everyone connects their hands with each other. 

Q7. What kind of a circuit can you form with one energy ball?

    My group formed a DC, which is direct current. because as the definition for DC is: the current flows in a single direction from the power supply to through the conductor to a load. We are actually making a circuit and the electric just moved through our body. It fits the definition for a DC.

Q8. Given 2 balls(combine two groups) can you create a circuit where both balls light up?

Yes! We joined another group and hold our pinkies together to make a circle(you always have to make a circle), just as what we did for the first one, the only difference is this time, we need two people to hold the balls. And it surely works~ we made both balls light up.  

Q9. What do you think will happen if one person lets go of the other person's hand and why?

When one person lets go of the other person's hand, that means the circuit is incomplete, since the circuit is incomplete, the ball won't light up. Because inside the ball, it is a DC current, when the current is disconnected, the electric ccannot transfer, so that the circuit won't be completed, and the ball won't be light up.

Q10. Does it matter who lets go? try it...

No, it does not matter. No mater who lets go, that means the ciecuit would be disconnected. Which indicates the electrons cannot pass on, and obviously the ball won't light up.

Q11. Can you create a circuit where only one ball lights(both balls must be included)

YES! In parallel circuit the above situation appears. As the picture shown below, in parallel circuit, even if one circuit is disconnected, there's still another circuit will be connected, in this situation, there's only one ball lights up, but there're really two light bulbs present.

Q12. What is the minimum number of people required to complete this?

 The minimum number of people that are required to complete this parallel circuit is 5.

                                                                                                                                                   
THE  DIFFERENCE BETWEEN A SERIES AND A PARALLEL CIRCUIT

The difference is that a parallel circuit has more than one path in the circuit,

and a series circuit only has one way around it.

【Blog#2】tall structures

Yesterday I built up a tall structure with Jess and Linda. First we thought that to make a stable structure, the base should be a close-to-triangle structure. So we rolled the newspaper and fold it to make a triangle structure as the base. Then we tightly rolled the rest of the newspaper (so the roll would be longer and taller) as the body of the tower. at first the structure cannot balance itself, but we don't want to kill the height of it, after our little discussion, we found out that the tower cannot stand because the top part was so heavy, so we decided to flip it over, we flipped the top of the newspaper to the bottom and taped it on the base so it stayed stable.




Now the question asks for the physics of tall structures, according to my experience, I'll say that the physics I tested out from the challenge is the mass of weight. As I said before, if the top part is heavier than the bottom part, the structure wouldn't be balanced. The less weight at the top, the more balance the structure will be. Another words, the base is important, the top is also important. We all know that the base should be heavier and bigger, such as the structure of a tumbler. But we often ignored the top part which is also an important part of the entire structure. as a result, the mass of weight is one of the physics of tall structures. For the second question: what makes a tall structure. I think this question is a bit similar as the first one. As I mentioned before, the more weight at the bottom, the more balance the structure will be. So for the purpose of making a balance tall structure, the first thing we'll need is a heavy and big base. And again, the body part should be light to make the whole structure stable. To sum up, the heavy base and the light body make a tall structure.



The centre of gravity is a geometric property of any object. In other words, the center of gravity is the average location of the weight of an object. For different shapes of objects, the centre of gravity is also different.

【Blog#1】Notes on Current Electricity

1. the definition for current is the rate of charge flow. it is a flow of negatively charged electrons repelling one another. and the equation for current is I = Q/t .

2. example#1:

    example#2:

3. the definition for conventional current is the model of positive charge flow.

4. current is flowing from the black negative(—) terminal to the red positive (+) terminal.

5.the electric potential difference is the difference in electric potential (V) between the final and the initial location when work is done upon a charge to change its potential energy. in equation form:V = E/Q. potential difference is often called voltage and the unit for this is the volt.

6.electric circuit is simply a closed loop through which charges can continuously move.for an electric circuit, the energy delivered to the load depends on the potential(energy per charge) and the rate at which the charge is delivered( the current). the energy transferred by charge flow is E = VIt.

7.how to draw circuit symbols? see textbook P547 for more info.

8.a direct current(DC), the current flows in a single direction from the power supply through the conductor to the load.(eg:light bulb)

9.a alternating current(AC), the electrons periodically reverse the direction of their flow. 

10.images of electric circuits.