Cheatography

# Physics Cheat Sheet (DRAFT) by sxdnxy

Basic physics with brief coverage of some topics.

This is a draft cheat sheet. It is a work in progress and is not finished yet.

### Repres­ent­ation of motion

 Motion Diagram Dots that are created in evenly spaced intervals. Larger gaps relate to larger velocity. Positi­on-Time Straight line represents constant velocity. Larger gradient large velocity. Free body Object is repres­ented as a particle with tails repres­enting forces. Tails represent direction and magnitude.

### Newton's Laws of motion

 1st Law If the forces are balanced then the object will maintain its current state of motion. 2nd Law Relati­onship stating net force is equal to the accele­ration times mass. More mass means increased resistance to change in accele­ration. 3rd Law Forces have action­-re­action pairs which are equal in magnitude but opposite in direction. These forces act on different objects.

### Thermal Physics

 Heat Transfer of thermal energy Temper­ature The average speed of all of the particles Heat flow continues until the average kinetic energy of each atom is the same.

### Geomet­rical optics

 Electr­oma­gnetic waves come in different wavele­ngths. Some within the visible spectrum and some outside of it. Reflection and transm­ission of waves occur at any change in medium that the waves travel through. The law of reflection The angle of incident light is equal to the reflected light Ray diagrams can be drawn to locate the position of the image Light bends in relation to the normal when the medium changes. Fast - Slow - Towards Slow - Fast - Away Refractive index and optical density both have an effect on light speed. The critical angle is when the refracted ray is 90 degrees to the normal. Meaning no light enters the second medium.

### Vectors vs Scalars

 Scalars - Physical quantities with magnitude but no direction. Scalars can be negative. Some examples are temper­ature, speed, energy and time. Vectors - Physical quantities with both magnitude and direction. Examples include forces, displa­cement, velocity and accele­ration.

### Useful equation

 Gravity F=mg 2nd Law F= ma Velocity v= u + at Displa­cement v= ut + 1/2 at2 Other v2=u2+2as Kinetic energy KE=1/2mv2 Thermal change Q=mc(T­2-T1) Ohm's Law V=IR Power P=VI, P=I2R, P=V2/R
v = final velocity
u = initial velocity
a = accele­ration
g = gravit­ational accele­ration
t = time
P = power
V = Voltage
I = Current
R = Resistance
T = temper­ature
c = heat capacity
s = distance

### Waves

 Logitu­dinal waves Contra­ctions caused by pushing and pulling Transverse waves Waves caused by up and down motions Frequency Number of crests in a given time Period Time between two identical points on a wave Wavelength Distance between two crests Speed increases in lower density and higher force mediums Superp­osition Sum of the two waves at a specific point Wavelength multiplied by frequency is equal to speed of the wave If speed increases frequency stays constant, amplitude

### Motion

 Time Total time that has passed since t=0 Time interval Difference between two times Distance Movement of object including double backs (Scalar) Position Location of an object relative to origin (Vector) Displa­cement A change in position (Vector)

### Energy

 Energy can be transf­erred across system boundaries through work, heat flow, or particle transfer. Work External forces cause movement in a system. Positive work causes movement in the same direction. Initial energy and work must always be equal to final energy.

### Methods of heat transfer

 Radiation Transf­erred through collision of particles Convection Occurs in fluids and relies on changes of density during heating. Radiation Heat travelling in infrared waves that can pass through vacuums.

### Electr­icity

 Positive charges can attract neutral objects Voltage potential difference - work done per unit charge Ohmic vs non-ohmic Ohmic resistors have constant resistant irresp­ective to the voltage across. In series the voltage changes across resistors and bulbs. Current stays constant. In parallel current splits and voltage stays constant. The more resistance you add in parallel the more current will flow. Voltage can be calculated by finding the previous voltage and subtra­cting IR of the resistor.