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MCAT > MCAT - Physics > Flashcards

MCAT - Physics Flashcards

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MCAT flashcards
1
Q

1 Angström

A

10^-10 m

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2
Q

1 electron-volt (1eV)

A

1.6x10^-19J

The amount of energy gained by an electron accelerating through a potential difference of one volt.

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3
Q

Vector

A

Magnitude & direction

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4
Q

Scalar

A

Magnitude only

distance, speed, energy, pressure, mass

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5
Q

Vector Addition

A

Use tip-to-tail method when the arrows are proportional to the magnitude

You can also break vector into x- & y-components:
x = vcos(θ), y = vsin(θ)
v = sqrt(x^2 + y^2) (Pythagorean theorem)
θ = tan^-1(y/x)

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6
Q

Vector Subtraction

A

Add one vector to another vector in an opposite direction
V = A-B = A + (-B)
Then continue with tip-to-tail method

You can also use component method

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7
Q

Vector x Scalar

A

B = nA

Multiplying by a scalar of the opposite sign will flip the direction of the vector

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8
Q

Vector x Vector

A 
Dot product (A . B): ABcos(θ)
Creates a SCALAR product
Cross Product (AxB): ABsin(θ)
Creates a VECTOR product, then use the right-hand rule to determine the direction of the resultant vector.
**AxB does not equal BxA**
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9
Q

Displacement (denoted as x or d)

A

Change of position in space. Vector quantity

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10
Q

Distance (d)

A

Scalar, entire path travelled

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11
Q

Velocity (v)

A

Rate of change of displacement. Vector quantity

Units (m/s)

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12
Q

Speed (v)

A

Rate of the actual distance traveled over time

Scalar

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13
Q

Force (F)

A

Push or pull. Vector

Units (N) 1N = 1 (kg x m)/s^2

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14
Q

Gravity (g)

A

Attractive force felt by all forms of matter
Fg = (Gm1m2)/r^2,
where G = 6.67x10^-11 (N x m^2)/kg

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15
Q

Friction

A 
Type of force that opposes the movement of objects. Opposite the direction of the motion.
-Static friction: μN
-Kinetic friction: μN
Static friction > Kinetic friction
Surface area doesn't matter
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16
Q

Mass (m)

A

Measure of a body’s inertia. Amount of matter in an object. Scalar

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17
Q

Weight (Fg)

A

Gravitational force on an object’s mass. Vector. Units (N)

Fg = mg

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18
Q

Acceleration (a)

A

Rate of change of velocity due to an applied force. Vector
a = Δv/Δt
Units (m/s^2)
Slope of the velocity vs. time graph = instantaneous acceleration

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19
Q

Newton’s 1st (N1)

A

Fnet = ma = 0

Inertia. Object will remain at rest unless acted on by a force

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20
Q

Newton’s 2nd (N2)

A

Fnet = ma. Nonzero resultant force vector will accelerate (a) a mass (m)

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21
Q

Newton’s 3rd (N3)

A

Fab = -Fba

Equal and opposite forces

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22
Q

Equations of linear motion (four of them)

A 
vf = vi + at
x = (vi)t + (at^2)/2
vf^2 = vi^2 + 2ax
x = vt
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23
Q

Air resistance

A

Like a friction. Objects in free fall will experience a growing drag force as the magnitude of the velocity increases. Eventually, the drag force will equal in magnitude to the weight of the object, it will fall at a constant terminal velocity.

24
Q

Projectile Motion

A

Motion along two dimensions.
Usually only vy changes due to gravity, vx is constant under negligible air resistance.
X and Y components are independent of each other

25
Q

Inclined Planes

A

Divide force vectors into components that are parallel and perpendicular to the plane.
Gravity must be split.
Fg(parallel) = mgsinθ
Fg(perpendicular) = mgcosθ

26
Q

Circular Motion

A

When motion is uniform, the instant. velocity vector is tangent to the circular path.
Object along a circular path has a tendency (inertia) to break out of the pathway.

27
Q

Centripetal force

A

Points radially inward, prevents the object from breaking into linear motion. Generates a centripetal acceleration.
Fc = (mv^2)/r

28
Q

Torque

A

Moment of force. Application of force at some distance from the fulcrum (fixed point a lever arm rests on).
Depends on the magnitude of the force and on the length of the lever arm (dist. b/n force and the fulcrum).
τ = r x F = rFsinθ
Clockwise = negative, Counterclockwise = positive

29
Q

Mechanical Equilibrium conditions (Translational motion, rotational motion, and torque)

A

Vector sum of all forces is zero.
Translational: constant velocity, speed, and constant direction
Torque: object is either not rotating at all or at constant angular velocity

30
Q

Energy (E)

Total Mechanical Energy

A

System’s ability to do work.

E = U - K

31
Q

Kinetic Energy (KE) or (K)

A

Energy of motion.
KE = 1/2mv^2
Units (J = (kg.m)/s^2)

32
Q

Potential Energy (PE) or (U)

A

Energy associated with a given object’s position in space or other intrinsic qualities of the system
Gravitational: Depends on object’s position w/respect to the ground (datum)
- U = mgh
Elastic: Springs and other elastic systems. When compressed or stretched from equil. length, it gains PE.
- U = 1/2kx^2

33
Q

1st Law of Thermodynamics

A

Conservation of mechanical energy.
Conservative forces: path independent, energy change is equal regardless of the path taken. ΔE = ΔU - ΔK = 0
Non-conservative: Like friction, energy is lost from the system in another form, like heat.

ΔU = Q-W
\+ΔU = increasing temp
-ΔU = decreasing temp
\+Q = heat flows into system
-Q = heat flows out
\+W = work done by the system (expansion)
-W = work done on system (compression)
34
Q

Work

A

Energy is transferred from one system to another.
W = F.d = Fdcosθ
Work done on or by a system can be determined by finding the area under pressure-volume graph. Pressure can be thought of as “energy density”

35
Q

Pressure-Volume Relationships

A
  1. Gas expands: work was done, work is positive
  2. Volume stays constant, volume changes (ΔV = 0): No work is done, no area under curve. *Isochoric/Isovolumetric
  3. Pressure remains constant as volume changes (ΔP = 0), area under curve is a rectangle. W = PΔV Isobaric
36
Q

Power

A

Rate at which energy is transferred from one system to another.
P = W/t = ΔE/t
Units (J/s)

37
Q

Work-Energy Theorem

A

Wnet = ΔK = Kf - Ki

38
Q

Mechanical Advantage

A

Any device that allows for work to be accomplished through a smaller applied force.
Mech. adv. = Fout/Fin
Fout = force exerted on object by simple machine
Fin = force actually applied on the simple machine
distance through which the smaller force must be applied INCREASES. Work DOESN’T CHANGE

39
Q

Simple Machines (6 of them)

A

Wedge, wheel axle, lever, pulley, and screw

40
Q

Pulleys (eq. of efficiency, how they work)

A

Apply a smaller force through a greater distance.
Efficiency: Wout/Win = ((load)(load distance))/((effort)(effort distance))
Load dist. is height you want to lift obj. It needs to be pulled a displacement twice that amount, the effort distance.
Adding six pulleys results in 1/6 the load, but you need to pull a length six time the desired displacement.

41
Q

0th Law of Thermodynamics

A

If first and second object are in thermal equil., and the second is in thermal equil. with the third, then the first and third are in thermal equil.
If a = b & b = c, then a = c.

42
Q

Temperature

A

Proportional to the average kinetic energy of the particles that makes up the substance. Spontaneous transfer of energy from high to low.

43
Q

3rd Law of Thermodynamics

A

Entropy of a perfectly-organized crystal at absolute zero is zero.
Δ1K = Δ1C
F = 9/5C + 32
K = C + 273

44
Q

Thermal Expansion (eq. of length and volumetric thermal expansion)

A

ΔT results in the change of a solid’s length.

  • ΔL = αLΔT, α = coeff. of linear expansion, units (K^-1 or C^-1)
  • ΔV = βvΔT (β = 3α)
45
Q

Isolated Systems

A

Not capable of exchanging energy or matter with their surroundings. Total change in internal energy is zero. Ex. bomb calorimeter

46
Q

Open Systems

A

Can exchange both energy and matter. Energy may transfer in the form of heat or work. Ex. boiling pot of water, humans, un-contained explosions

47
Q

Closed Systems

A

Capable of exchanging energy, but not matter, with the surroundings. Ex. gases in vessels with movable pistons.

48
Q

2nd Law of Thermodynamics

A

Objects in thermal contact not in thermal equil. will exchange heat energy from high to low until they both have same temp.
Units of heat: 1 Cal = 10^3 cal = 4184 J = 3.97 BTU

49
Q

Conduction (heat transfer)

A

Direct transfer of energy from molecule to molecule through collisions. Must be in direct contact.

  • Metals are best heat conductors b/c rapid energy transfer due to sea of e-
  • Gases are poorest b/c collisions occur infrequently
50
Q

Convection (heat transfer)

A

Transfer of heat by physical motion of a fluid over a material. Convection involves FLOW, so only liquids & gases can transfer heat this way. Ex. running a cold water bath to cool rxn

51
Q

Radiation (heat transfer)

A

Transfer of heat by electromagnetic waves (EM). Can occur through a vacuum. Ex. the sun

52
Q

Specific heat (c)

A

Amount of heat energy required to raise one gram of a substance by one degree C or K. Changes according to an object’s phase.
q = mcΔT
Units (1 cal/g.K) or (4.184 J/g.k)

53
Q

Heat of Transformation

A

Phase changes occur at constant temp. Temp will not change until all of the substance has been converted from one phase into to the other.
q = mL, where L = latent heat
Heat of fusion and heat of vaporization

54
Q

Adiabatic

A 
Q = 0
ΔU = -W
55
Q

Entropy

A

Measure of spontaneous dispersion of energy at a specific temp.
ΔS = Qrev/T
Work must be done to concentrate energy
Net entropy change is zero in physically reversible rxns

MCAT (1 decks)

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