Physics Flashcards
Blueprint MCAT Prep
What are the key SI prefixes?
deci (-1), centi (-2), milli (-3), micro (u, -6), nano (-9), pico (-12)
Kilo (3), mega (6), giga (9), tera (12)
What are the trigonometric functions?
SOH CAH TOA
Describe the difference between scalars and vectors
Vectors have magnitude AND direction, while scalars only have direction
When splitting velocity into X- and Y- components, which trigonometric functions do you use?
Vx = vCos()
Vy = vSin()
What is the key component of adding vectors?
X components must only add with X components, while Y components can only add with Y components
Displacement
Change in location; is a vector quantity (scalar equivalent is distance)
Velocity
Change in displacement over time; is a vector quantity (scalar equivalent is speed); area under the curve of a velocity vs. time graph is displacement
Acceleration
Change in velocity over time; is a vector quantity; area under the curve of an acceleration vs. time graph is change in velocity
What is acceleration in free fall?
-9.8 m/s2
What is Vy at the top of a projectiles trajectory?
Vy = 0
What is force
Something that causes an object with mass to accelerate
Newton’s First Law
Inertia; An object remains at rest or a constant velocity within a reference from unless an external force acts upon it
Newton’s Second Law
Defines Force; States that the total sum of forces acting on an object, also known as the net force, is equivalent to its mass times its acceleration
Newton’s Third Law
Force comes in pairs; Every action has an equal and opposite reaction
Explain some key points to remember about free body diagrams
Free body diagrams work with center of mass and draw out all forces acting on an object; Forces act from center of mass; Resolve non-perpendicular forces using trigonometry; Solve using Newton’s laws (mainly 1st and 2nd)
Static Friction
When object isn’t moving; A certain amount of force must be applied to break static friction
Kinetic Friction
When object is moving
Is more force needed to overcome static friction or kinetic friction?
Static friction
Gravitation
A force of attraction between objects with mass (know equation); Note that force of gravity is proportional to mass and inversely proportional to the square of the distance between the objects
Centripetal Force
Causes rotational motion; Common examples are gravity (eg. satellites in orbit) and tension force (mass on a string)
Hooke’s Law
Force needed to compress/stretch a spring by x is F = -kx, where k is a constant unique to each spring that represents its stiffness
Torque
Can be though of as rotational force; Know equation; Be aware of static equilibrium with torque: You may need to balance clockwise and counterclockwise forces
Work
Defined in units of energy (Joules)
What is the difference between conservative and non-conservative forces?
With conservative forces, such as gravity, work is path-independent (displacement); Non-conservative forces are path-dependent (distance) and include friction and air resistance
Mechanical Advantage
Less force –> same work
Power
Work divided by time (units are Watts)
Kinetic Energy
Know Equation; Energy due to motion
Potential Energy
Energy an object has stored within itself; Can be gravitational, elastic, electrical, or magnetic
Conservation of Energy
Energy can neither be created nor destroyed, just transferred from one form to another. This is a basic law of nature, no exceptions have been found
How do non-conservative forces affect conservation of energy?
Non-conservative forces like friction may remove energy from a specific system that we’re interested in modeling, which may be dissipated as thermal energy, but the physical law of conservation of energy is still followed
What is important to note about the equation for conservation of energy? Why is it particularly significant
Note connection between conservation of energy and the kinematic quantities of v and ∆y - this means that conservation of energy can be used to efficiently solve some kinematics problems; For some problems, you can choose between the strategies of kinematics equations or conservation of energy; Kinematics equations are needed if you need to account for time, and conservation of energy is needed if the physical setup is too complicated to apply MCAT trigonometry (eg. rollercoster)
What does the work-energy theorem link?
Work-energy theorem links work and kinetic energy; Very effective way to solve problems were you need to link work/energy with change in velocity
What does the area under the curve represent in a graph relating pressure and volume?
Work = area under the curve of a graph with pressure on y-axis and volume on x-axis; Common Application: use of pistons to compress gas
Heat
A form of energy transfer
Temperature
A way of measuring the average kinetic energy of the particles that much up a substance; Heat and temperature and NOT the same thing
What temperature does water freeze & boil in Fahrenheit; What is normal body temperature?
Water freezes at 32°F, boils at 212°F, and normal body temperature is 98.6°F
What temperature does water freeze & boil in Celcius; What is normal body temperature?
Water freezes at 0°C, boils at 100°C, normal body temperature is 37°C
Open Systems (Thermodynamics)
Open systems can exchange matter and energy with their surroundings
Closed Systems (Thermodynamics)
Closed Systems can only exchange energy with their surroundings
Isolated Systems (Thermodynamics)
Isolated systems can exchange neither energy nor matter with their surroundings. Arguably the only true example is the universe, although we may try to simulate isolated systems in various contexts
State Functions vs. Path Functions
Describe the state of a system at a given moment, while path functions describe transitions
Zeroth Law of Thermodynamics
If System A is in thermal equilibrium with systems B and C, then systems B and C must be in thermal equilibrium with each other (essential for explaining temperature)
First Law of Thermodynamics
Conservation of Energy; Energy change of a system = transfer of energy in the form of heat minus work done by system on surroundings
Second Law of Thermodynamics
Deals with increasing entropy over time; If two objects are in thermal contact, but not in thermal equilibrium, heat energy will spontaneously flow from the object with the higher temperature to the object with the lower temperature; The entropy of an isolated system will increase over time; Microscopically, entropy is a measure of how many micro states are compatible with a given macro state, or a measure of degrees of freedom of the molecules within a state of matter
Conduction (Heat Transfer)
Direct transfer between substances in contact with each other
Convection
Heat transfer due to circulation of fluids (liquids or gas)
Radiation
Does not require direct contact between two substances (Sunlight = thermal radiation)
Thermodynamic conditions relevant for PV Curves
Isobaric: Pressure Constant
Isothermic: Temperature Constant
Adiabatic: No heat or matter transfer
Isochoric: Same Volume
What is the Density of Water?
1000 kg/m3 = 1 kg/L = 1 g/mL = 1 g/cm3
Describe the mechanical advantage in a hydraulic lift
Idea is that same volume of fluid is being moved, but the force necessary depends on area
Surface Tension
Caused by uneven intermolecular interactions at an interface between two surfaces
Cohesive Forces vs. Adhesive Forces
- If cohesive forces within a molecule are stronger than adhesive forces to walls of a container, a convex meniscus results (mercury)
- If adhesive forces to walls of a container are stronger than cohesive forces within a molecule, a concave meniscus results (water0
Viscosity
ON an intuitive level, viscosity = resistance to flow (technically resistance to deformation by shear stress). Water is relatively non-viscous
Laminar Flow vs. Turbulent Flow
Laminar Flow = Flow of smoothly regulated layers
Turbulent Flow = Chaotic
What key relationships can be derived from Bernoulli’s Law & continuity equation?
Narrow tube = lower pressure (Venturi effect), higher velocity
Higher Velocity = Lower pressure
What is a Pitot Tube used for?
Pitot tube can be used to calculate velocity of a fluid
Charge
A property of subatomic particles; electrons are negatively charged, and protons are positively charged; Like charges repel, opposite charges attract
Field Lines
Field Lines in an electric field point in a direction that a positive charge would move
Dipole
Substance with two stable charges at each end
- Dipole in a uniform electric field will align with electric field lines
Electric Potential Energy
Measure of how much work is needed or is performed to drag a charge from infinity to a given location within an electric field
Electric Potential (V)
A measure of electric potential energy normalized for charge
Equipotential Lines
Lines connecting points with equal elctric potential; no work is done moving charge along equipotential lines
Current
Charge over time (1A = 1 C / 1 s)
Is electromotive force (emf) a force?
No
Resistance
Units of Ohms (1 V / 1 A), resistors convert current to other forms of energy in a circuit (heat or light)
Ohms Law
V = IR
Capacitors
Store charge in parallel plates
Dielectric Insulators
Increase capacitance
What kind of electric field do capacitors create?
Capacitors create a uniform electric field
Magnetic Fields
Generated by magnetic materials and moving charges, can affect MOVING, CHARGED particles
How do you find the direction of magnetic fields?
Given by right hand rule when generated by a current (thumb points in direction of current, while curled fingers represent magnetic field around the wire)
How do you find direction of force of a magnetic field on a moving charge?
2nd Right hand rule; Right hand rule with thumb for motion of charge, fingers for magnetic field, and curled fingers for direction of force for a POSITIVE charge (opposite for negative)
Periodic Motion
Displacement is y, periodic motion is t (in time), frequency (f) is in 1/T (Hz)
- Conservation of Energy: at peak all energy is PE, and at equilibrium point (y = 0), all energy is KE. Periodic motion involves a constant interplay between KE and PE
Transverse Waves
Motion of particles is perpendicular to direction that the wave is moving in. Classic examples include waves in water, as well as light/electromagnetic waves
Longitudinal Waves
Motion of particles is parallel to direction that the wave is moving in. Classic example is sound.
Interference
When waves overlap, amplitudes add together
- Constructive Interference: Amplitudes in same direction add up for increased overall amplitude
- Destructive Interference: Amplitudes in opposite direction cancel each other out, either totally or partially (dampening)
Velocity of waves in different materials
Velocity of waves is different in different materials
What does the velocity of sound depend on?
Velocity of sound depends on bulk modulus (B) and density (p)
- Bulk modulus measures how much pressure is needed to compress a substance by a certain amount
- Takeaway Point: Sound moves fastest in non-compressible materials (solids), slower in liquids (because they are more compressible), and slowest in gas (because it is most compressible). Speed of sound in air is 343 m/s
Intensity
Intensity is defined in terms of power (W) divided by area
Decibels Definition
Decibels are a logarithmic measure of intensity
Doppler Effect
Waves get “bunched up” or “stretched out” (i.e. frequency increases or decreases) from the perspective of an observer depending on the motion of the observer and the source.
***Signs with Doppler equation can be tricky: Do a reality check based on the physical setup, and whether you expect waves to be bunched up or stretched out, whenever you are doing a Doppler problem
Standing Waves
Occur when waves reflect back in a constrained medium. Harmonics. Draw them out.
Strings and Pipes (waves)
Strings and open pipes have different patterns of nodes and antinodes (nodes on both ends for strings, antinodes on both ends for open pipes)
Light
Light is an example of an electromagnetic (EM) wave; in EM waves, electric and magnetic components are both perpendicular to propagation direction and to each other; can be polarized
EM Spectrum
HUGE range of wavelengths; visible light is ~400-750 nm
Object’s Apparent Color
The apparent color of an object is due to the light wavelength it doesn’t absorb
Reflection
When a light wave bounces off of an object; Angle of incidence equals angle of reflection
Refraction
Angle of light in a new medium changes due to a change in velocity
Remember, in optics, all angles are to the normal
Light moving between different mediums
As light moves from a medium with a larger index of refraction to one with a smaller angle of refraction (meaning that it is speeding up), total internal reflection can occur past the critical angle
Diffraction
When waves move through a barrier with a small opening, they spread out
Concave vs. Convex Mirrors and Lenses
Concave mirrors curve in; Convex mirrors curve out
Real vs. Virtual Images in Mirrors
SEE TABLE ON PHYSICS BOOK PAGE 163
Positive Lenses
Positive (convex, converging) lenses cause light waves to bend towards each other
Negative Lenses
Negative (concave, diverging) lenses cause light waves to bend away from each other
Real Images
Formed by real rays and are inverted
Virtual Images
Back-traced and upright
