Electric Field

In todays class we learned about an electric field.


An electric field is a region in space where a force is exerted on a positive test charge.  It is a region that would cause a test charge to move if it were placed within the region.

Electric Lines of Force- lines that represent the direction that a freely moving positive test charge will move in an electric field.  These lines originate at positively charged objects and terminate at negatively charged objects.


The strength of on electric field is shown by the distance between field lines.  The filed is stronger when the lines are closer together.

The field lines want to be as far part as possible from each other.  When the charge is negative the field lines will point towards it and positive they will point away format he charge.

1st ~ B < A

2nd~ C < D

3rd~ G < E < F

4th~ J < H < I

We determine this by the number of field lines coming off or going to the charges.

Next is Kurtis

Electricity and Coulomb's Law

Today in class we talked about how Coulomb's are the SI unit of a charge.

1 C= 6.24 x10^18 Electrons   1 Electron= 1.60 x10^-19

So the charge of one electron is called the Elementary charge. This charge is also the charge of 1 proton.

To find the charge on an object we use the formula  Q = Ne 
                                                                              Q= the quantity of charge
                                                                              N= number of elementary charge
                                                                              e=  the elementary charge (always 1.60 x10 ^-19

Ex.    Calculate the charge on a metal-leaf electroscope that has an excess of 5.0 x10^10 electrons.

Q= ?                                                                   Q= Ne
N= 5.0 x10^10                                                   Q= 5.0 x10^10 (1.60 x10^-9)
e= 1.60 x10^-9                                                   Q= -8.0 x10^-9C


Coulomb's Law


This is the formula which is applied to find the magnitude of the force of repulsion or attraction between two charges.
                                                                          F=K q1q2
                                                                                   d^2


F= electrostatic force
q= charge (C)
d= distance (m)
k= 8.99 x10^9Nm^2/C^2 (always)

A negative force implies an attractive force.
A positive force implies a repelling force.

krystle is next

Into Electricity!!!

In today's class we were introduced to the unit of Electricity. We used textbooks to match terms with their definitions. From this, we established:



Elementary Charge- the magnitude of the charge on a single proton or electron.

 e=1.602x10^-19C, where C= 1 coulomb



Electric Circuit- A closed-loop conducting path, consisting of a source of electrical energy, a conductor, and a load, which utilizes the electrical energy.



Conductor- known to have an electrical charge because it has excess or a deficiency of electrons. The charge is distributed over the surface of the conductor because of the similar charges’ repulsion.



Electric Current- the rate of which charges flow at- passing through a cross-sectional area in a conductor. It is considered to be a flow of positive charges.



Ammeter- used to measure the electric current in an electric circuit, and is connected in a series with the circuit.



Schematic Diagram- a plan or design which represents the components and their relationship to one another by symbols



Direct Current- the continuous flow of electrons in the same direction



Alternating Current- periodic reversal in the direction of the flow of electrons



Fundamental Law of Electrical Charges:

-opposite electric charges attract each other

-similar electric charges repel each other

-charged objects attract neutral objects



Conduction- is the process in which a neutral object gains a charge through contact with a charged object



Induction- an electrically charged object being used to create an electric charge on another object without touching.



After learning about these concepts, Mr. Banow proceeded to show demonstrations of  Electrostatics. He did so by showing the transferring of charges between a balloon, wall, and sweater. We ended the class with Mr. Banow experimenting with a Van de Graff Generator.



Next is Ryan J

Gravitational Potential Energy and Total Energy

In Wednesday's class, we did not really do anything but answer the questions from page 290 #1-4 for the whole class.

In Thursday's class, we started the class by reading the pages 291-292 in our textbook about Potential Energy and Law of Conservation of Energy. After that, we then proceed and read through our notes about Gravitational Potential Energy and Total Energy.

Gravitational Potential Energy (Eg) is the energy that is stored when an object is placed in a vertical  position relative to the ground level (which is the surface of the earth or the floor of any room), or any base level.

The formula you can use to find the Eg of an object is:

Eg = mgh

where:

Eg = Gravitational Potential Energy (Joules or J)

m = the mass of an object (kg)

g = acceleration due to gravity (9.8 m/s^2)

h = change in height relative to the reference point (m)

*** There are other types of potential energy but in this class, when potential energy is mentioned, only gravitational potential energy is usually used.

Ex. A hydraulic hoist lifts a 1100 kg car 2.5 m. What is Eg?

m = 1100 kg 

h = 2.5 m

g = 9.8 m/s^2

Eg = ?

Eg = mgh

Eg = (1100kg)(9.8m/s^2)(2.5m)

Eg = 27000 J

After talking about gravitational potential energy, we also talked about Total Energy. 

In an object, there will be an equivalent increase in gravitational potential when work is being done. When an object is raised, potential and kinetic energy interchanged which means when one of the energy would increase, the other one would decrease. The sum of kinetic and gravitational potential energy remains constant in any system, and the total value of energy remain constant (Law of Conservation of Energy).

Etotal = Epotential + Ekinetic

Note **** Friction and Air Resistance are ignored in Conservation of Energy.

Examples:

1. Roller Coasters

- There would be most potential energy or gravitational energy at the highest point of a roller coaster (and there is zero kinetic energy) 

- At the lowest point, kinetic energy is when it has its maximum value (or zero potential energy)

2. Pendulums

- The distance from equilibrium is like the height above earth.

3. Springs

- There are more Elastic Potential Energy a spring has when it is further deformed. 

- The formula you can use to find elastic potential is: 

Ep(elastic) = 1/2kx^2

k = the spring constant (every spring has a specific k value)

x = how far from the equilibrium the spring is depressed or stretched (also called Hooke's Law)

Ex. A compressed spring that obeys Hooke's Law as a potential energy of 18 J. If the spring constant of the spring is 400 N/m, find the distance by which the spring is compressed. 

Ep = 18 J

k = 400 N/m

x = ?

Ep = 1/2kx^2

(2Ep)/k = x^2

(2(18J)) / 400 = x^2

36/400 = x^2

x = 0.30m

Kinetic Energy( It Moves!)

In yesterdays class we learned more about energy and its different forms. We learned that

• Kinetic Energy (Ek) is the energy of motion
• Potential Energy (Ep) it the energy of rest
• Change in energy = Final Kinetic Energy - Initial Kinetic Energy (if on a level surface)
• Work = change in kinetic energy
• Ek = 1/2mv^2
• kinetic energy is a scalar quantitiy
• its SI unit is Joules(J)

ex. 1 If an 8.0 kg mass moves at 35m/s what is its kinetic energy?

Ek = 1/2(8.0kg)(35m/s)^2  Ek = 4900J

We also learned more about collisions.

• An Elastic Collision is when there is no loss of energy.(rarely happens)
• An Inelastic Collision is when there is some energy lost 
• An Completely Inelastic Collision is when two objects stick together  

Physics Works

We began the class of May 14th by reviewing the concept of Work(W). The key ideas of this concept are:

• Work is the product of an applied force and the displacement of an object in the direction of the applied force.
• Work is a scalar quantity
• The SI unit of Work is Joules (J)
• If there is no applied force, there will be no work done
• If there is no displacement there will be no work done

We then proceeded to do some example problems.

ex.

A boy pulling a wagon is exerting a force of 20.0 N at an angle of 35 deg to the horizontal. If he pulls it 100.0 m along the ground, calculate the work done.

Cos35 =   Fax                                                                          W = Fd

              20.0N                                                                        W = (16.38 N[fwd]) (100.0m[fwd])
Fax = 16.38 N [fwd]                                                                W = 1600J



   We also learned that work can be calculated from an applied force vs displacement graph by finding the area underneath the graph. However, estimation is sometimes needed when a graph is curved.

  We continued with the day's lesson by learning about Energy (E)

• Energy is the ability to do work
• When work is done, energy is transferred from one object to another
• Unit is Joules
• An increase of Energy of an object means that the work done on it will be positive and vice versa
• Not all Energy is used when it is converted from one form to another
• Energy efficiant products minimize lost Energy

***Time does not change the amount of work done, it does however tie into POWER***

What is Power (P)?

• The rate at which work is done
• The rate at which energy is used
• SI unit is the watt (W)
• Power = work
•                time
• The more time it takes to complete a task, the less power is had.

Ex:
A man does 120 J of work in lifting a box from the floor to the table. If it took 2.0 s to perform the task what is his power?

W = 120 J                                         P = W                       P = 120 J              P = 60. W
 T = 2.0 s                                                  T                               2.0s
 P = ?

And thus concludes the class that took place on Monday May 14th, 2012
 <-- work done!

YAY work

Good day everyone. On Friday we started a new chapter in physics, all to do with work, power and energy. We started by listing what we knew about the topic and came up with several pieces of information including:

• It takes energy to do work
• You get energy from food 
• Electricity is a form of power (Steam power, coal power)

We also discussed kinetic and potential energy, kinetic energy being the amount of energy an object has while it is in motion and potential energy being the amount of stored energy and object has.

Example of Potential Energy:

Holding a football above the ground, has potential energy due to the force of gravity because if you let go, the ball will fall to the ground. The higher you hold the ball the more potential energy the football has.

Work:

After discussing the informtion we already knew about the subject we finally defined Work as the product of an applied force and the displacement of an object in the direction of the applied force. In other words it is when we apply a force to an object and the object moves in the direction the force was applied or in the opposite direction.

W=Fd 

W= work F=force d=displacement

Unit = Joules (J)

If there is no applied force upon an object or there is a displacement of zero, no work has been done. For example if you pushed all day on a wall but the wall has not moved, you have made no progress therefore you have done no work.

Also no work has been done if the force being applied and the displacement of the object are perpendicular to one another. For example a satellite orbiting the earth, the satellite is moving forward around the earth but gravity is pulling the satellite down, by definition it is not work.

Positive work- when the applied force and the displacement act in the same direction

Negative work- when the applied force and the displacement act in opposite directions

We followed all of this great knowledge with some examples.

1. Find the work required to lift a 3.0x10^3 kg object to a height of 5.0 m?

F=mg                                                   W=Fd

F= (3.0x10^3 kg)(9.8 N/kg)                W=29400 N x 5.0 m

F= 29400 N                                         W=15000 J

d= 5.0 m

W= ?

2. A person pushes a loaded box 55.0 m by exerting a horizontal force of 35.0 N on the box. How much work is done?

d= 55.0 m                                            W=Fd

F= 35.0 N                                            W= 35.0 N x 55.0 m

W= ?                                                    W= 1925 J = 1930 J (significant digits)

(If the object is not being lifted we do not have to worry about mass x gravity as in example 1.)

Conservation of Momentum!

In Thursday's class we learnt about the laws of conservation of momentum. We learnt that initial momentum is equal to final momentum. An isolated system is one where no external net force acts on the system. There are four types of explosions and collisions.

1. Explosion from rest: M1V1 = -M2V2
2. Explosion from motion: (M1+M2)Vi = M1Vf1+M2Vf2
3. Elastic Collision: M1V1i+M2V2i = M1V1f+M2V2f
4. Inelastic Collision: M1V1i+M2V2i = (M1+M2)Vf

Example: A 0.205 kg hockey puck moving at 51 m/s is caught by a 80.0 kg goalie at rest. With what speed does the goalie slide on the ice?

M1V1i+M2V2i = (M1+M2)Vf
Vf = M1V1i / M1+M2
Vf = (0.205kg)(51m/s) / (80.0kg+0.205kg)
Vf = 0.13m/s



Next up is Susanne

Impulse And Momentum!

Yesterday we already had our Labs set up and went straight to work. We began our Impulse and Momentum labs. The objective were to 1. Measure a cart's momentum change and compare to the impulse it receives. 2. Comapre average and peek forces in impulses. We began the lab by using the web quest and a cart connected to an elastic band  finding final velocity, and  initial velocity on the lab quest. From here we could determine change of velocity. We then took the average force which helped us to find durations of impulse and the impulse.  From the lab we took down the data and were able to compare and constrast Impulse and change of momentum. We found out that  mpulse equals the change in momentum.

Next up is Ty.

FREE FALL AND MOMENTUM!

On Friday's class we finished up learning about free fall and terminal velocity. We then started learning about momentum. Momentum can be described as "inertia in motion". The more mass and velocity an object has, the more momentum. This can be found through the formula p=mv.

ex. What is the momentum of a 1 kg piece of fecal matter being flung by a monkey at 15 m/s [E]?
    m= 1kg                              p=mv
    v= 15 m/s [E]                    p= (1 kg)(15 m/s[E])
    p= ?                                   p= 15 kgxm/s [E]

On monday's class we started setting up for impulse and momentum lab. We answered some general question about momentum and how if an object is in contact with a force for a longer period of time, it will have more momentum.

Next up is Dylann. Sorry my blog post sucks.