Constructive vs. Destructive Sound Waves

It's been a while since we had to blog! Here we go,

This one is about the difference between constructive and destructive waves.

First, some background knowledge: When two or more waves interact with each other at the same time, a new, combined wave is created. This interaction is known as wave interference and there are two types of wave interference.

1. Constructive Interference.
This is when the interacting waves coming together are moving in the same direction (when one wave upwards, the other waves upwards as well). The combination of these two waves will strengthen each other and produce a wave that adds the intensity of the combined waves. (e.g if one wave moves up one centimeter and the other wave moves up one centimeter, the combined wave will move up two centimeters)



Constructive Interference

 2. Destructive Interference
This is when the interacting waves that are coming together are moving in a different direction (when one wave moves upwards, the other moves downwards). This combination will interfer with each other destructively. The intensity of the combined wave is lowered and the amplitude is shortened in length. (They subtract) 

Destructive Interference

I recently came across this funny video of a cannon...

http://www.youtube.com/watch?v=Bo8Q88bAXyQ

LOLOLOLOLOL HAHAHAHA

Different Types of Energy

Energy is something that's all around us, in everything. The reason it has the ability to be in anything is because there are so many forms of it. Firstly, the two main forms are potential energy and kinetic energy.

This has a lot of potential energy

Kinetic Energy is the energy of a moving object. It considers the mass and velocity of the object when calculating the energy.

Potential Energy is the energy that the object has the potential of producing. There are many forms of this, the most simple being gravitational potential energy. That is when the object is not on the ground; it has the potential to accelerate towards the ground by gravity.

There are many more types of energy that root from potential and kinetic, they include: mechanical energy, heat energy, chemical energy, elastic energy, sound energy, and nuclear energy.

Mechanical energy is the combination of potential and kinetic energy. It is the energy associated with the motion or position of an object.

Heat energy is pretty much in everything. Unless the molecules of the particular item isn't moving at all, there will always be heat energy; although some things seem really cold, their molecules are still moving, although they are moving very slowly. It can be either potential or kinetic energy

This has potential energy too (elastic)

Chemical energy is produced when a chemical reaction occurs; it is a form of potential energy, because it involves energy that an object has the potential of producing.

Elastic energy is another form of potential energy produced when something is stretched out. It has the ability to return to its original shape, causing energy.

Sound energy is a form of kinetic energy. It is caused by movement, mostly a vibration that travels through a specific medium. The pressure is what usually causes the sound.

Nuclear energy is a form of potential energy since its the energy stored in specific atoms. Two types exist: nuclear fusion and nuclear fission. Nuclear fission is when the atoms and molecules release energy when they split while nuclear fusion is when atoms produce energy when they are joined together. Nuclear fusion normally occurs at very high temperatures

cannons shoot stuff

Currently, in the wonderful physics class of Mr. Chung, we are required to prepare cannons that fire STUFF out of just cans and duct tape. How? Well I don't really know but here is what i do know about cannons:


-Cannons shoot stuff to cause DESTRUCTION
Throughout history, cannons have been pretty much the oldest style of artillery fire used for warfare. They fire heavy objects at incredible speeds, (Force=mass x acceleration according to Newton) which means that they fire with a lot of force. Therefore, they have the capability to do incredible damage.


-The ammunition for a cannon should be round and smooth.
Throughout history, the ammunition used for cannons have evolved for a simple cannonball (just as the name suggests it's a sphere...) to missile shaped objects. The reason for this is because the object that is utilized has to counteract air resistance as good as possible to fire the longest distance possible at the greatest speed possible. Round and smooth objects can carve through the air better than boxy and bumpy objects.


-Kinematics equation for Range is a good equation to use to determine the maximum distance the cannon can fire.

(d=V1²sin2θ/g)

-Cannons should be placed at a 45 degree angle to the horizontal to maximize the distance fired.

This is because increasing the angle will increase airtime for the projectile while the angle can't be increased too much since it won't fire forward anymore. For example, if the cannon is pointed at over 90 degrees, the projectile will fire backwards (into your own people...) while a 90 degree angle will cause the projectile to fire straight up (and it lands into your own people...) and an angle higher than 45 degrees won't have as much of a velocity in the x-axis. This means to achieve the most ideal distance, a 45 degree angle should be utilized.

Newtons Problems

These days in physics class, we're learning new stuff about Newton. First of all, he devised 3 laws:

1. The law of inertia : Things don't like to stop doing what they're already doing (lazy) e.g if the object is moving it doesn't like to stop and if the object is still, it doesn't like to get up and move.

2. Force = Mass x Acceleration

3. For every action, there's an equal and opposite reaction.

With these three laws, there are many different questions known as "Newton Problems" that can be devised. The four simplest ones being objects in equilibrium, objects static on an incline, objects kinetic on an incline, pulleys, and trains.

EQUILIBRIUM

When an object is considered to be in "equilibrium" it means that the object is in a state where all the forces acting upon it are balanced and it is stationary. No acceleration in the x OR y direction is present.

Therefore, for these types of questions, the resultant Force (net force) should equate to zero; or at least very close to 0.



An object in equilibrium



Assumptions for equilibrium questions:

-no air resistance/friction

-no acceleration in the x or y direction

-1 free body diagram in total

-Fg = mg = m(9.8) = Fn, in which Fn is the force keeping the object up

-there's a constant positive axis

-forces acting on the x-axis are equal on both directions





STATIC INCLINE

When an object is static while being on an incline, this means that the object is on a slant, at an angle just before the force of gravity overcomes the force of the friction pulling it back. The object is still in equilibrium, there is no acceleration in either the x or y direction.

Therefore, for these sorts of questions, the sum of all forces acting upon the object should still equate to 0.

Assumptions for static incline:

-no air resistance

-no acceleration in the x or y direction

-1 FBD

-positive axis on a slant dependent on the direction the incline is facing (if the incline is like /, the left will be positive)

-Friction static = miu static x Force normal, in which miu static is the coefficient of friction in this case (also the tan of theta [the angle measured for the incline])

-gravity is split into the x and y component (y is usually opposed by the normal force and x is usually opposed by friction)

KINETIC INCLINE

When the object is kinetic on an incline, this means there is acceleration and there IS motion of the object (due to gravity) as opposed to static when the object is held still by friction. In this case, there is also friction, but it is overpowered by gravity.

For these sorts of questions, the net force no longer sums to 0. There will be a direction of travel. 

Assumption for kinetic incline: 

-no air resistance

-acceleration is consistent (not 0)

-1 FBD

-positive axis on a slant dependent on the direction the incline is facing (the direction the object travels)

-Friction kinetic = miu kinetic x force normal, in which force normal is equivalent to the force of gravity (y), which is in turn the mass of the object multiplied by gravity (9.8)

-gravity > friction (that's why the object is moving)

PULLEYS

A pulley is a tool where there are two objects (yes that means 2 free body diagrams now) where they are connected by a rope of cable of some sort. This means that the side with the heavier object will dominate the side with the lighter object.

The net force should not be 0 unless the mass is equivalent on both sides of the pulley.

Assumptions for pulleys:

-frictionless pulley

-frictionless rope/cable

-no air resistance

-2 systems -> 2 FBDs

-T1=T2 (the tention on both sides of the pulley should be equivalent due to Newton's 3rd law)

-acceleration is the same in the y direction

-positive axis on the direction of travel (one side will be going down, and one side will going up)



TRAINS

Trains are pretty much pulleys, except rather than having movement on the y-axis, their movement is on the x-axis. BTW trains are exactly what they sound like (chugga chugga chugga choo choo) One mass pulling the rest.

Net force is in one direction, and greater than 0 because friction is overpowered by the applied force.

Assumptions for trains:

-2+ FBD (as many as there are parts added)

-no air resistance

-acceleration in the y-axis = 0

-cables weightless

-the direction of the + axis is the direction of acceleration

-acceleration is consistent

Projectile Motion

So for the past two days, physics class was composed of determining projectile motion

On the first day, we all attempted an experiment with a marble and a ramp on a table. The marble was rolled off the ramp, and the elapsed time was taken from the point the marble left the table to the point it hit the ground.

On the second day, we just learned the conceptual stuff behind projectile motion.

So basically, when an object it released at speed, the gravity is taken into account while the object slowly drops.
However, there are two points in which to take into consideration. The first one being the movement on the x-axis (horizontal movement), and the second one being the movement on the y-axis (vertical movement). The horizontal movement is always at a constant velocity (the velocity at which the object was released), and the vertical movement requires the addition of gravity (9.81 m/s²). Usually, the vertical component begins with a V1 of 0, because it is dropped onto the ground, therefore, there is no initial velocity. Also, the height of the object is usually the distance the y component travels before it hits the ground.

Furthermore, the elapsed time of the x component should be equivalent to the time for the y component. Knowing these facts, many different pieces of information can be obtained using the big 5 equations.

That is a brief summary of projectile motion :)

Rollercoasters are Fun

Mostly, people don't really care about the physics of rollercoasters or how they work. They just enjoy going on them because they're FUN! :) However, being the curious student that I am hehehe... I am interested in how they work.

That guy has the BEST reaction EVER!

Believe it or not, rollercoasters do not have engines to propel them at the exhilerating speeds they go at. Instead, they are brought up by a track to the highest point of the coaster. At the top, they are released and for the rest of the ride, they are just released and left to travel on the power of gravity. In other words, when the coasters are being brought up, they obtain potential energy. The potential energy is then converted into kinetic energy on the way down. Sounds familiar? This concept is the Law of Conservation Energy. For rollercoasters to continuously move, the altitude has to continuously drop.

To answer the question of my favourite rollercoaster, the one that I've been on that I like the most is probably the SkyRider at Wonderland. I don't even know why, but it just felt the most fun. It isn't the fastest rollercoaster, the tallest one, but for some reason, I like it the most. Also, in my opinion, the faster the rollercoaster... the better it is!! WEEEEEEEE