Wave interference

Waves interfere when one wave passes through another.

Constructive interference: when a crest meets a crest or a trough meets a trough
The shape of the wave formed is determined by the sum  of the seperate amplitudes of each wave.
Animation : http://zonalandeducation.com/mstm/physics/waves/interference/constructiveInterference/InterferenceExplanation2.html

Destructive interference: when a crest meets a trough.
The shape of wave formed is determined by the sum oftheamplitudes of each wave.
Since the postive amplitudes from one crest are added to the negative amplitudes from the other trough, the addition will look likea subtraction.
Animation: http://zonalandeducation.com/mstm/physics/waves/interference/destructiveInterference/InterferenceExplanation3.html

Different types of energy

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There are different forms of energy, but they can generally be divided into two groups: potential and kinetic energy.

A. Potential energy - stored energy and energy of position
- Chemical energy - energy stored in bonds of atoms and molecules
- Gravitational energy - energy stored in an object's height
- Elastic energy - energy stored in objects by tention e.g compressed springs and stretched rubber bands

B. Kinetic energy - motion of waves, molecules, objects, substances, and objects
- Mechanical energy - energy stored in movement of objects
- Thermal energy - vibration and movement of atoms and molecules within substances
- Sound energy - movement of energy through substances in longtitudinal (compression/rarefaction) waves

Reference: http://www.eia.doe.gov/kids/energy.cfm?page=about_forms_of_energy-forms

Cannon... Σ(ﾟДﾟ；

Found a useful simulation for projectile motion~
http://phet.colorado.edu/sims/projectile-motion/projectile-motion_en.html

After a few trials, it is discovered that the launge angle of 45 degree enables the bullet to travel the maximum distance...

Then I found that, the larger the velocity the cannonball has, the longer the distance it can travel...

Some websites said that a longer barrel gives a higher velocity to the cannonball since the long length of the barrel gives a longer distance for the ball to gain acceleration. But for the cannon we are going to make, the cannonball is places at the exit of the cannon so I think this theory may not be useful here...

Newton problems

1. Equilibrium

Assumption:
-Positive axes
-∑F = 0 ( ∑Fx = 0 , ∑Fy = 0), a = 0
- no friction
- no air resistance
- rope is weightless

When calculating, divide all the force to x-axis and y-axis,
Fx = max        Fy = may
Fx = 0              Fy = 0



2. Inclines

(a) object is at rest
Assumptions:
- postive is along the incline direction
- ∑F = 0, a = 0
- no air resistance
- FN is perpendicular to incline
                     ∑F = ma 
∑Fx = max                ∑F = may
∑Fx = 0                       ∑F = 0
Fgx - f = 0                 FN - Fgy = 0




(b) object is moving
Assupmtions:
- positive is along the incline direction
- ∑Fy = 0 , ∑F is not equal to 0
- no air resistance
- FN is perpendicular to incline
use the same method of calculation as when object is at rest

3. Polley

Assumptions:
- polley is frictionless
- rope is frictionless and weightless
- no air resistance
- 2 systems (2 FBDs)
- T1 = T2
- a of the system is the same (ay1 = ay2)

Note that ∑Fx = 0 for both objects
Do the calculation by dividing the foerces into x and y.


4. Train

Assumptions:
- Use 3FBDs  to find T
- no air resistance
- ay = 0
- cables are weightless
- positive is in the direction of a
- a is consistant

Assume the whole system as an object to calculate the acceleration
Then use 3 FBDs to find tension amoung the masses


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