Physics MCAT Flashcards
4 major kinematic equations
Acceleration of centripetal force
a = (v^2)/r
Centripetal force
The force that is responsible for rotational motion. This can be gravity (orbital) or force of tension that the string exerts on the mass (the mass is tied to a string and swung around).
Definition of torque
Rotational force, caused by a force applied to a lever arm at a certain distance from an object capable of rotating.
Formula to calculate torque
t = Fdsin(θ); with θ is the angle btw the lever arm and the force applied.
Definition of Force
An interaction that can cause an object (mass) to accelerate.
F = ma
Unit: N or kg*(m/s^2)
Definition of Work
The transfer of energy that occurs when an object is moved with a certain displacement.
Unit: Joule (J) = N*m
W = F*d
Angle btw applied force and direction of movement
Conservative force
Path-independent; the amount of work done by a conservative force does NOT depend on its path. Care abt displacement only!
Ex: gravitation, spring force, electromagnetic force,…
Non-conservative force
- dissipate energy
- path-dependent
Ex: friction, air resistance, viscosity
PV Work (another equation for work)
Assume constant pressure, Work a gas does against piston to expand its container.
W = External pressure * Change in V
W = P * delta(V)
If pressure changes, Work = area under the curve of graph of pressure (y-axis) and volume (x-axis).
Mechanical advantage
Allows us to deploy less force, but does not do less work!
We apply less force than it would otherwise be necessary to perform a certain amount of work.
Ex: seesaw, inclined plane, pulley, lever
General formula of mechanical advantage
Mechanical advantage for inclined plane
Mechanical advantage = Length of incline / Height of incline
Mechanical advantage > 1. If = 1, no mechanical advantage.
The more angle increases, the more we shorten length of incline. So it decreases overall mechanical advantage
Power
Power = the rate at which work is done; work per unit of time
- More quickly, more powerful
P = W / delta(t)
Unit: watts (W) = J/s
Power of an object maintaining a constant velocity despite a force opposing that motion
Formula of gravitation force and spring force
Kinetic energy
All objects in motion have kinetic E
Formula of Gravitational and Elastic potential energy
Conservation of energy
Conservation of Energy for non-ideal system
When a system loses energy to environment, it’s due to non-conservative forces (friction, air resistance)
Work-Energy theorem
The work performed on or by an object is equal to the change of its kinetic energy.
- In an ideal system, the magnitude of work done by object A on object B equals the magnitude of work done by object B on object A.
What does (+) work mean?
+ Work done on an object by its environment
+ Increase object’s energy
+ Energy put into a system
What does (-) work mean?
- Work done by object on its environment
- Decrease object’s energy
- Energy taken out of a system
Convert Celsius degree to Kelvin
Celsius = ( T + 273) K
O C = 273 K
Relationship btw Celsius and Fahrenheit
oF = (9/5) C + 32
Reduction potential
Tendency to undergo reduction (willingness to gain electrons)
More positive value, greater tendency to gain electron
Cathode and Anode
Red Cat And Ox
Cathode is where REDUCTION takes place
Anode is where OXIDATION takes place
Calculate reduction potential of a cell (Ecell)
Ecell = Ecathode - Eanode
Unit: V
T/F
Reduction potential of galvanic (voltanic) cell is always positive so that its redox rnx is spontaneous.
True
Calculate specific gravity (SG)
SG = Density of objection / Density of fluid
SG > 1 -> Obj sinks
SG = 1 -> Obj in equilibrium with fluid
SG < 1 -> Obj floats
Doppler effect
When a sound source is approaching an observer, the perceived frequency of the sound increases, resulting higher pitch. This is because the sound waves are compressed as the source moves closer, causing the wavelengths to appear shorter.
When a sound source is moving away from an observer, the perceived frequency of the sound decreases, resulting lower pitch.
Define current (I)
Current = the rate of flow of electric charge. Current flows from (+) pt to (-) pt of voltage.
I = q / t
Unit: A = C/s
Define Voltage (V)
Voltage = the electric potential difference btw 2 pts
Ohm’s Law
V = I*R
V: voltage
I: current
R: resistance
Calculate resistance (R)
Calculate Power
P = I*V
Unit: Watts (W)
A circuit with resistors R wired in SERIES:
A circuit with resistors R wired in PARALLEL
How to wire ammeter to measure current
An ammeter is wired in series into a circuit.
Ideal ammeter has 0 resistance.
How to wire voltmeter to measure voltage
A voltmeter is wired in parallel into a circuit.
Ideal voltmeter has extremely high resistance.
What is an idealized capacitor?
- Capacitor is for storing charges.
- Consist of 2 parallel conductive plates separated by a non-conductive, insulating material (dielectric material).
- Capacitor creates uniform electric field (E)
Capacitance
The degree to which a capacitor can store charges
Capacitance C = Q / V
or Q = C * V
Unit: Farad (F)
F = C / V
Calculate capacitance based on area and distance
Dielectric constant k and modified capacitance C’
Electric field (E)
Direction: same as the direction of positive test charge movement; from positive to negative
Strength of electric field
Potential energy (PE) of capacitor
Capacitors wired in SERIES
Capacitors in PARALLEL
Gases deviate from ideal gas behavior at a
Low T and high pressure
General formula to calculate mechanical advantage (MA)
Which force keeps protons together in the nucleus? (overcome repulsive force btw same-charge particles)
Strong nuclear force
Binding energy of a nucleus
A potential energy
- the minimum amount of energy required to disassemble nucleons
- how much less potential E the whole nucleus has compared to the sum of its individual components
Calculate binding energy of nucleus
Mass defect
The difference btw predicted mass and actual mass.
- Principle of mass energy equivalence: some of the subatomic particles’ mass is converted into energy. That is why the actual mass is lower than the predicted mass.
de Broglie equation (Planck const, wavelength, mass and velocity)
Heisenberg uncertainty principle
The more precisely we know about the position of a particle, the less precisely we know abt its momentum.
- Provide the answer why electrons dont collapse into the nucleus
Photoelectric effect
A substance (usually metal) emits electrons in response to a beam of photons being shined onto it. The energy of incident photons is absorbed by the material and excites electrons to the point that they are ejected from their atoms.
Note: Frequency-dependent (threshold frequency) for this effect to occur
Calculate energy of a photon
Work function in photoelectric effect
The minimum amount of energy needed to expel an electron from an atom of a substance.
What if a metal is hit by a photon carrying more energy than the bare minimum necessary to eject the electron?
Extra energy can go towards the kinetic energy of the electron
T/F
Intensity of light corresponds to the number of photons in that light
True
Rydberg equation
R is Rydberg constant
In which condition (energy level) does energy (photon) is absorbed?
When an electron is being excited to a higher energy level
Ex: from n = 1 to n = 2
In which condition (energy level) does energy (photon) is released/ emitted?
When an electron is dropping back down to a lower energy level
Ex: from n = 3 to n = 2
5 main types of radioactive decay
Radioactive decay formula
(The amount of material remaining at time t)
The fraction of material remaining after n half-lives
Alpha decay
Alpha particle (helium nuclei) is emitted.
Beta-minus decay
Neutron is converted into a proton, so the atomic number increases by 1: Z + 1
An electron is ejected to maintain charge balance
Beta-plus decay
Proton is converted into a neutron, so atomic number decreases by 1: Z - 1
a positron (e+)/ beta-plus particle is emitted to preserve charge.
Gamma decay
Emit gamma ray (light), which is a high-energy photon, from an excited nucleus
No atomic number or atomic mass change.
Electron capture
Nucleus grabs an electron, changing a proton into a neutron.
Atomic weight stays the same, but atomic number Z decreases by 1: Z - 1
Calculate remain and how much sample is lost, knowing numbers of half-lives n
Calculate reduction potential Ecell
Spring-related formula: Fspring, PEelastic, periodic motion
Kinetic energy and root mean square of velocity
1st law of thermodynamics
Total energy in an isolated system is constant.
The change in entropy due to a reversible process
Conduction
Heat is directly transferred btw 2 substances placed in direct contact with each other, mediated through the transfer of kinetic energy from the particles of one substance to those of the other.
Convection
Direct transfer of kinetic energy/ heat transfer from one substance to another due to the circulation of fluids.
Radiation in thermodynamics
Energy is transferred via electromagnetic waves; not require direct contact btw 2 substances.
Thermal expansion
Heating a substance generally causes it to expand.
Exception: ice is less dense than water.
Formula for linear expansion and volume expansion
Work in terms of pressure and change of volume
2nd law of thermodynamics
Why must the person either lean forward or slide their feet under the chair to stand up?
To keep the body in equilibrium while rising.
Venturi effect
The reduction in fluid pressure that results when a fluid flows through a constricted section of a pipe.
Example of Venturi Effect
