Constructive vs. Destructive Interference

We are now officially at the last unit relating to physics. This unit deals with waves and sound. Particularly we will be discussing constructive and destructive interference....sounds complicated??? Well hope I will be useful.

When two or more sound waves are released from different sources , and travel relatively at the same time, eventually they will interact with one another creating a new wave. The new creative wave is the sum of all the waves added together. This interaction between the waves is called, wave interference. There are two types of interference constructive and destructive interference. 

Constructive interference is when either the crests or the troughs of the two waves that are moving toward each other, interfere. It is important to mention that the two waves have to have the displacement in the same direction. When this happens the wave gets amplified , therefore producing a louder sound. In other words, the combined pattern of the waves is the sum of the individual wave outlines.

Constructive interference: Crest & Crest

Constructive interference: Trough & Trough 

On the other hand, destructive interference is when the two interfering waves have a displacement in the opposite direction. For a better understanding, destructive interference occurs when the crest of one wave , meets with the trough of the other wave. When interfering the new created wave will have a lower intensity, this is because the positive crest of one wave is added to the negative trough of the other wave, which results in a subtraction.

Destructive interference: Crest & Trough

*As Mr. Chung pointed out, it is important to remember that if the displacement of two waves is in the same direction (doesn't matter either negative or positive) it will still be a constructive interference .

Different Types of Energy

All about energy

Thermodynamics is the study of energy. Energy is the ability to do work. Work, is the process of energy transfer. Based on the first law of thermodynamics energy or matter can neither be created nor destroyed. There are a lot of different forms of energy and therefore when they change from one another work is being done on the object. These are some of the basics from of energy. 

Kinetic Energy

The two main types of energy are kinetic energy and potential energy. Kinetic energy it's a object in motion relative to the ground and is abbreviated as KE. The equation for calculating the kinetic energy of an object is KE = ½ mv² . We know that this type of energy exist, because we could see the different objects moving. If a soccer ball flies through the air it has kinetic energy, because it is moving. The faster the ball will move, the more kinetic energy it will have. 

 

Potential Energy

When holding an object at a distance from the floor, it has the potential to start moving, once letting it go. The force of gravity is pulling on the object, giving it potential energy. The equation is PE = mgh. This type of energy could be stored. 

Thermal or Heat energy

One type of kinetic energy is the thermal or heat energy. When holding a cup of coffee, it is believed to have "thermal energy "or "heat energy" which is really kinetic energy at the molecular level (the molecules have kinetic energy because they are moving and vibrating. Temperature is really a measure of how much thermal energy something has. The higher the temperature, the faster the molecules are moving therefore the more kinetic and potential energy the molecules have. 

Mechanical Energy

Mechanical energy is the sum of energy in a mechanical system. Is the energy that is held by an object due to its motion or due to its position.  Mechanical energy can be either kinetic energy (energy of motion) or potential energy (stored energy of position).When thinking about a moving baseball we have to account both mechanical energy due to its high speed (kinetic energy) and its vertical position above the ground (gravitational potential energy).

Chemical energy

Chemical energy is the potential of a chemical reaction to occur or to transform other chemical substances. The energy that is stored in chemical bonds is released when chemical reactions occur. 

Sound Energy

Sound energy is the energy produced by vibrations of the object as they travel through a specific medium. Because of movement of the object, this is a type of kinetic energy. The movement of sound depends through which material it travels. The denser the material, the harder for the sound to go through it. 

Gravitational Energy

Gravitational potential energy is the energy possessed by an object 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 acceleration due to gravity is assumed to be about 9.8 m/s2.When thinking about an water fall the energy was saved as potential energy in the gravitational field of the Earth and was released out of storage as the water dropped. When the water dropped, the energy was converted into kinetic energy. 

Elastic potential energy

This basically  is potential energy stored as a result of deformation, stretching or bending  of an elastic object, such as the stretching of a spring, bands, rubber  . The amount of elastic potential energy stored in the object is related to the amount of stretch done on the object - the more stretch, the more stored energy.

The Best Cannons in History

Cannons

The first cannons appeared in the early 14th century in Europe. It didn't undergo a lot of changes since then. The basic structure of cannons is basically a strong cylinder permanently closed at one end, while temporary closed by a cannonball at the other end. Between this two ends a explosive charge was placed. When the charge was inserted through the touch-hole, it exploded in the direction needed.  Back in time people used cannons for smashing a wall, killing men, horses and bombing ships . 

 

When looking back in time, we see a lot of different types of cannons that were built in different times and by different people.  Some of the most impressive cannons are:

1. Gustav Gun - The Largest Gun Ever Built

The largest gun ever built was the "Gustav Gun" built in Essen, Germany in 1941 by the firm of Friedrich Krupp A.G.

2. The Tsar cannon

 

It is a huge gun commissioned in 1586 by the Russian Tsar. The cannon weighs nearly 38 metric tonnes and has a length of 5.34 meters (17.5 feet). The Guinness Book of Records lists it as the largest howitzer ever made. The cannon has never been fired and it may have been intended as a military showpiece. 

3. Armstrong 100 Ton Gun in Malta (1457)

One of the largest bore cannon ever built (bore is twenty inches).

4. The Crimean war Cannon in Odessa

Newton's Laws and Applications

Newton's Three Laws

1. Newton's First Law: Law of Inertia:

An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

Ex: Imagining a satellite traveling through space . It will want to continue traveling  forever, and it will do so unless the satellite will crash into something( unbalanced force).

2. Newton's Second Law: F = ma

The acceleration of an object is directly affected by its mass and how much force is applied to it. The greater the mass of a specific object, the greater the forces need to accelerate the object. 

Ex: For example, it is easier for a strong adult to push a full shopping cart than it is for a baby to push the same cart. (This is depending on the net force acting on the object.) Also, it is easier for a person to push an empty shopping cart than a full one. (This is depending on the mass of the object.)

3. Newton's Third Law:

 

For every action force , there is an equal and opposite reaction of the force.

Ex: An example could be a rocket. The rocket's action is to push down on the ground with the force of its powerful engines, and the reaction is that the ground pushes the rocket upwards with an equal force.

Applying Newton's Laws to four types of problems:

I order to solve the followings problems assumptions are needed to be present. After having them it is important to draw a Free Body Diagram = FBD, to show all the forces that act on the specific object. It will help in answering the question and understanding it. 

Equilibrium: when the forces acting on an object are balanced. In order to solve these types of problems , assumptions are needed to be done.

Assumptions:

no friction 

T1x=T2x  

a = o therefore ax = 0                            

ay = 0

 

Inclines (static): when the object is almost ready to move, but still not moving

Assumptions:

Fn - perpendicular to the surface                                        

acceleration = 0                                                       

positive axis are in the direction of acceleration

no air resistance

Inclines (kinetic): in these types of problems , the object is moving but only horizontally. Kinetic friction is created by the mass accelerating.

Assumptions:

no air resistance

positive axis in the direction of acceleration

Fn - perpendicular to the surface

acceleration is not equal to 0

ay = 0 

 

 

Pulleys: 

Assumptions:

no friction

the rope also has no friction

no air resistance

2 FBD's

T1 = T2

acceleration is the same for both masses

positive axis in the direction of acceleration

   

Trains: These types of problems are similar with pulleys, the only difference is that they are placed horizontally. The main cabin of the train will have an applied force.       

  

Assumptions:

positive axis in the direction of acceleration

1 FBD for acceleration(imagining the train asa a single dot on FBD)

3 FBD's for T1 & T2

no air resistance

the cable is weightless

ay = 0

acceleration is constant

 

Last important tip, in order to solve the problems, it is needed to split the FBD's into x and y components. Then solve for the variables needed.