Friday, December 10, 2010

Different types of energy!!

Everything have different types of energy and there are many energy acting on many object such as, kinetic energy, potential energy, gravitation potential energy, energy, elastic energy, thermal energy, mechanical potential energy, nuclear energy, and chemical energy.


Kinetic Energy→↓
The kinetic energy of an object is the energy which it possesses due to its motion. 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.

Potential energy→↓
Potential energy is one kind of the energy that we learned in our physics class. Potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. We calculate potential energy in J (joule). It's the SI unit of work and energy. The term "potential energy" was coined by the 19th century Scottish engineer and physicist William Rankine.

Gravitation energy→↓
Gravitaion energy is the energy that act on any object in the world due to the gravity. If an object falls from one point to another point inside a gravitational field, the force of gravity will do positive work on the object, and the gravitational potential energy will decrease by the same amount.

Thermal energy→↓
Thermal energy is the energy that makes objects hot. It is a form of kinetic energy at the molecular level, the movements of atoms and molecules. It is the translation of two different energy. For example, Hot water has more kinetic energy then cold water because there are more molecule acting in the hot water than the cold water.
Elastic energy→↓
Elastic energy is the potential mechanical energy stored in the configuration of a material or physical system as work is performed to distort its volume or shape.


Chemical Energy→↓
  Chemical energy is the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances. Breaking or making of chemical bonds involves energy, which may be either absorbed or evolved from a chemical system.


CANNON!

To make the best cannon, it's back to the projectile moetion problems, cannon is highly related to the projectile motion. To make a better cannon, we should have a good angle and the inside of the cannon should have less friction, so the deceleration would be less. Although we are not using the gunpowder in our experiment, but we could use alcohol so the power would be less and it would be more safe to do the experiment. In this experiment, the force that's acting on our cannon ball would apply to Newton's first law and it might travel 1~ 4m. As there a velocity on the cannon ball causes by the cannon, it would turn up to be the concert of projectile motion. Best way to make the angle of the cannon is between 40 to 50 degree.

Newton's Problems

 There are four kinds of Newton's problems that we learned in our physics class, those four are equilibrium, incline, pulley, and train.

Equilibrium happens when there are no acceleration acting on the object and the positive force are equal to the negative force.

Assumptions→↓
 -no air resistance
- no acceleration  ax = 0   ay = 0
- T1y = T2y = mg
-one free body diagram
-Set positive axises
The second Newton's problem is incline. There are two different types of incline, static and kinetic.

Incline (static)
Assumptions→↓
-no air resistance
-no acceleration
-Fn is perpendicular to the surface
-Fgy - Fn = 0
-one free body diagram


The only different between static incline and kinetic incline is the change of acceleration. In kinetic incline, there is acceleration.

Assumptions→↓
- no air resistance
-Acceleration not = 0
-positive in the direction of acceleration
-Fn is perpendicular to the surface
-one free body diagram
-Fn - mgy = 0



Pulley

Assumptions→↓
-pulley is frictionless
-rope frictionless
-no air resistance
-2systems>2 FBDs
-T1 = T2
-a of the system is the same
-positive in the direction of acceleration



Train

Assumptions→↓
-positive in direction of acceleration
-3 FBDs
-no air resistance
-cables weightless
-a is consistant


 

Projectile Motion!

To calculate a projectile motion problem, initial velocity, final velocity, accerleration, time, and distance are included, but the mass of the object is excluded. The key to solve the projectile motion problems is to break in two components, the horizontal and vertical component.
As we know that the gravitational acceleration is 9.8m/s². The acceleration in the y-component is always 9.8. If the speed of the obeject would be constant in the x-component. As we know that the speed acting on the object is just begin, the initial velocity/ the highest point of the object in y-component would be 0.
There are 4 types of projectile motion, the first type would be an object from the top and a force acting on the horizontal component. This kind of projectile motion can be solved by determining the time. In this case, the initial velocity of y-component is always zero and the velocity in x-component is always constant.
※The first type of projectile motion

The second type of the proejectile motion would be an object that has a velocity against the gravity. In the highest point of the whole projectile system, the velocity would become zero and the acceleration is determined as negative 9.8.

The third type of projectile motion also would be an object that have a velocity that against the gravity. But in this case, the displacement in y-component is not zero any more, there would an positive number in the y-component.

The last type of projectile motion is an object that habe a velocity that against the gravity and end with a negative displacement in the y-component.




PHYSICS BEHIND ROLLAR COASTER

  I go to wonderland often because of the rollar coaster. I am a really big fan of rollar coaster, but I haven't known about the physics behind rolllar coaster before the physics class.

  The physics in the rollar coaster is due to the gravitational force and the apply force acting on it. The friction in the rollar coaster is also an very important part of a rollar coaster. Without friction, the rollar coaster might not able to stop and the people wouldn't be able to step forward. Anthor physics behind rollar coaster is the energy of the collar coaster. As we know, Many energy in acting on an obect, the most affective energy that act on the collar coaster would be potential energy and the kinetic energy. As the rollar coaster is pulled on the top, a porential energy is created and once the rollar rolls from the top, the potential energy would transferred to both kinetic and potential energy.

Tuesday, October 26, 2010

How to add vertors

To determine the resultant : As we add straight vectors (※subtracting vectors means adding a vector in the opposite direction) , we would find the closest distance between the origin and destination. That would be our resultant. According to the Pythagorean Theorem, a² + b² = c², which "c" represents the hypoteneuse.

To determine the angle : The easiest way to measure the angle accordance to N or S is to use the protactor. But in this course, we would recommand to use the Trigonometry Theorem, Cos, Sin and Tan.



 To determine the vectors components: First, we set the positive axes, then break all vectors down into two components ( x and y). We calculate the total of x and y and follow the step as above (To determine the resultant, To determine the angle )

Thursday, October 21, 2010

How equation#4 derived from the V/T graph















In Equation #4, only V2 is usable. In another way to calculate the area of the trapezoid, we could calculate the area of the trangle and subtract the area of the triangle.   That would come out the equation #4, which is d=V2Δt-½aΔt².

Equation #4  ────  d=V2Δt - ½aΔt²
                                   ↓            ↓
                              Rectangle    Triangle


To determine the area of the rectangle, we would multiple V2 (as symbol "b" shown in the graph《Height》)  to t2 - t1, which known as Δt. (as symbol "h" shown in the graph《Height》)

It will give us an equation,
Area of Rectangle = V2Δt

To determine the area of the rectangle, we would multiple (V2 - V1) 《Base》to  Δt 《Height》divided by 2.

According to Equation #1  = V2 - V1, so, as we sub this equation,
                                         V1= V2 -  aΔt

Area of triangle = ½(V2 - V1)(Δt)
Area of triangle = ½(V2 - V2 - aΔt)Δt
Area of triangle = ½(- aΔt)Δt
Area of triangle = -½aΔt²

Displacement = Area of rectangle - Area of triangle (As we sub the equations in,)

Displacement = V2t + ( -½aΔt²)

Displacement = V2t - ½aΔt²