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Flashcards in Physics 2 Deck (71):
1

  • Think of a "FIELD" as:

  • an invisible influence capable of exerting a force on a MASS or CHARGE

2

  • Universal Law of Gravitation (formula)

Fg=Gm1m2/r2

3

  • The Universal Law of Gravitation is true everywhere, but NEAR EARTH'S SURFACE:
    1. What do we assume?
    2. What formula can we simplify to?

  • Assume g= 10 m/s2
    • Simplify to:
      • F=mg

4

  • Give the PEgrav formula NEAR EARTH

For FLUIDS (which DON'T always move as a single uni), what change to the formula do we make?

PEgrav=mgh

  • For fluids:
    • use PEgrav=pgh
      • p=density=m/v

5

  • Give the PEgravformula
    • IN SPACE, or
    • NEAR EARTH'S SURFACE 
      • if we AREN'T assuming g=10 m/s2

PEgrav= - Gm1m2/r

Radius is NOT squared here!!!

6

  • Friction opposes ____, not ____

SLIDING!

  • ​not motion

7

  • If theres SLIDING, it's ___ friction
  • If NOT, its ___ friction

  • sliding= kinetic friction
  • not sliding=static friction

8

  • Give the formulas for static & kinetic friction

STATIC FRICTION:

  • Ff=UsFn ​
    • or Ff=Usmgcosθ

KINETIC FRICTION:

  • Ff=UkFn
    • or Ff=Ukmgcosθ

​Us / Uk = Coefficient of static/kinetic friction

Fs / Fk= Force of static/kinetic friction

n= "normal force"=mgcosθ

 

 

9

  • Define MAX static friction

  • once this value is reached, OBJECT BEGINS TO SLIDE
    • at this moment, we now have kinetic friction, NOT STATIC 

Ex: no mvmt at 500 N (static) but starts moving at 501 N=kinetic 

10

  • Inclined Planes
    • Give the equation for:
      • Force down an inclined plane
        • parallel to the surface

F=mgsinθ

11

  • Inclined planes:
    • Normal force on an Inclined Plane
      • Equation=?

Fn=mgcosθ

12

  • Inclined planes:
    • Velocity of a particle at the base of an inclined plane
    • Equation=?

Vf=√2gh

13

  • Inclined planes
    • ACCELERATION down an inclined plane
    • Equation=?

a=gsinθ

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14

Hooke's Law formula

F=kΔx

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15

  • How do you calculate k (spring constant) by hanging weights?
    • Remember calculation is different for just doing ONE trial and doing TWO (+) trials

  • Solve using Hooke's Law
    • F=kΔx
    • for Δx, use:
      • Displacement from equilibrium point 
        • for ONE trial
      • Difference in displacement 
        • between TWO trials
    • For F, use:
      • Force applied in ONE trial, or
      • Difference in force
        • between TWO trials
  • Remember to convert mass of object to force
    • using F=mg

16

  • PEelastic 
    • Definition
    • Equation=?

PEelastic=½kΔx2

  • PEelastic= PE stored in a compressed spring

17

  • PEelastic most likely used for what kinds of questions?
  • How would you use PEelastic to find out how far a spring compresses when an object hits it?

Conservation of energy questions!

  • When a mass of velocity V hits a spring:
    • ALL of its KE is converted into PEelastic
    • Setting KEinitial equal to final PEelastic
      • ...lets you find how far the spring will compress

18

  • Kinetic Energy equation=?

KE=½mv2

19

  • Finding how far a spring compresses
    • What COMBINATION of formulas would you use?

Set KE equal to PEelastic

  • ½mv= ½kΔx2

20

  • ONE CYCLE of a pendulum is?
    • (LOTR)

  • "There and back again"

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21

  • For a pendulum to exhibit Simple Harmonic Motion (SHM)...
    • What value must be LOW?

  • Angle of displacement

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22

Give 3 examples of Simple Harmonic Motion

  1. Pendulum
    • mass on a string
  2. Things w/ circular motion when viewed from the side 
    • Ex: Something bobbing up & down in the water
      • has a circular motion! 
  3. Waves sloshing back & forth in a container

 

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23

  • Simple Harmonic Motion 
    • Give the Mass on a Spring formula

T=2π√m/k

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24

  • Simple Harmonic Motion
    • Give the pendulum formula

T=2π√L/g

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25

  • Simple Harmonic Motion
    • What is "T?" 
    • What thing is its inverse?

T=period

  • inverse to frequency 
    • f=1/T

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26

  • Objects at rest are in ___ equilibrium

STATIC equilibrium

27

  • Objects moving at CONSTANT velocity are in ___ equilibrium

DYNAMIC equilibrium

28

  • What do you do to solve equilibrium problems?
    • Hint: make a T...

Make a T

  • put opposing forces on opposite sides
  • balance them out

 

  • Ex: If 180 N in downward direction
    • then 180N upward

29

  • Give 3 examples of equilibrium

  1. Terminal velocity
    • mg=Fair
  2. Constant velocity
  3. Objects at rest

30

  • Torque formulas3 variations)
    • Break down what each part represents

  1. T=fl
  2. T=mgl
  3. T=Frsinθ​
    • l=lever arm
    • r=dist b/t force & point of rotation

31

  • In Torque equation:
    • r = l only when...?
    • What is always equal to "l?"

r = l only when θ=90°

  • "rsinθ"  is always equal to l

32

  • To solve for:
    •  fulcrum and boards on strings problems
      • Hint: these are in equilibrium

Set:

  • Tclockwise=Tcounterclockwise
    • include ALL torques!

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33

  • Torque
    • In what scenario would you use T=Frsinθ?

  • When Force applied is NOT perpendicular to the surface
    • i.e., when θ is NOT 90°

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34

  • Define:
    • systems NOT in equilibrium

  • where the object has NON-ZERO ACCELERATION

35

  • When solving for systems NOT in equilibrium:
    • How do you solve it differently than systems that are in equilibrium?
    • What can you IGNORE when solving for systems that are not in equilibrium? 

  • Solve in same way as equilibrium problems (T method
    • but add "ma" to the "losing side"
      • This equals it out

You can IGNORE SIGNS (+/-) when you do this method! 

36

  • Equilibrium on an Inclined Plane
    • How to solve?

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Use T method

  • One side= UP forces

  • Other side=DOWN forces

    • Down forces always equal to F=mgsinθ
      • since force of friction is always parallel to the plane opposite the direction of motion

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37

How to solve problems involving 2D forces

Use T method

  • Put formula that predicts component of each force into boxes
  • Add "ma" onto the "losing side"

38

Define the "right hand rule" for angular velocity (ω)

  • Curl fingers around axis of rotation, so that fingers are pointing in the direction of rotation
    • Your thumb will then be pointing in the direction of the vector (ω)

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39

How many radians per 1 revolution 

~6

  • 6.28 exactly

40

How to convert Radians to degrees 

  • 2π radians/360°

or

  • π radians/180°

41

  • An object is in rotational equilibrium IF:
    • 2 options...either one or the other

  1. It is NOT rotating, or
  2. It is rotating with constant ω (angular velocity)

42

  • Momentum formula=?

p=mv

43

  • Think of momentum as?
    • When is it always conserved?

...as INERTIA INCREASED BY VELOCITY

  • p is always conserved in an isolated system
    • is not conserved when not in an isolated system

44

  • Define "Impulse"

  • change in an object's momentum 
    • "Δp"

45

  • Impulse formula
    • 3 variations (in order of how you should think of impulse)

  1. I=Δp
  2. I=mΔv
  3. I=Favgt

46

  • What are common impulse questions?
    • How are velocity and impulse related?

CAR CRASHES!

  • No change in V= No impulse
  • High change in V=High impulse

47

  • Elastic vs Inelastic collisions

Elastic Collisions

  • p AND KE conserved

Inelastic Collisions

  • p conserved ONLY

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48

  • If object is deformed during collision, it was a _____ collision

  • inelastic

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49

  • Elastic collisions
    • Equation=?
    • Hint: What gets conserved during elastic collisions?

½m1v12+ ½m2v22= ½m1v12+ ½m2v22

  • p and KE both conserved

50

  • For PERFECTLY elastic collisions, what 2 weird things happen?
    • What's a (albeit imperfect, but close enough) example of this?

  1. Speed is conserved
    • before AND after collision
  2. If mass of 2 objects is equal but they have different velocities:
    • velocities get exchanged
      • in order to conserve momentum (p=mv)

Think of: BILLIARD BALLS

51

  • Inelastic collisions formula
    • What thing DO you need to remember to use here that you DON'T need to use for elastic collisions?

m1v1+m2v2=m1v1+m2v2

You need to remember to USE SIGNS!! (+/-)

  • Velocity has a negative sign when:
    • going to the LEFT or
    • DOWN 

52

  • "Perfectly INelastic" collisions
    • definition & formula

  • objects collide and stick together
    • it's like MARRIAGE!
  • if they move after collision, they do so together

m1v1+m2v2=(m1+m2)v3

53

  • Reverse Collisions definition
    • What is commonly use by the MCAT to test you on reverse collisions?

  • Two objects start out together and come apart
    • it's like DIVORCE

Common examples:

  • Bomb exploding
  • Also, RADIOACTIVE DECAY is frequently used 

54

  • Thermal expansion formula

ΔL=αLoΔT

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55

  • Heating solids leads to ___
  • Cooling solids leads to ___

  • expansion
  • shrinkage

56

  • What makes water unique when it comes to thermal expansion?

  • When temperature of water gets close to zero, it EXPANDS (INSTEAD OF SHRINKING)
    • because of of highly ordered lattice structure of ice
      • This is why the solid ice doesnt sink on liquid water

57

  • PEelec
    • formula=?
    • 2 variations

  • PEelec=Kq1q2/r

or

  • PEelec=qEd

58

  • PEcapacitor formula=?
    • 3 variations

  • PEcapac=½QV 
  • PEcapacitor=½CV2 
  • PEcapacitor=½Q2/C

59

  • Internal energy
    • definition

  • Energy of:
    • Internal vibrations &
    • Random motions of:
      • molecules and/or
      • atoms w/

...in a system

60

  • Heat energy
    • Definition
    • Where can Heat Energy come from? (2)

=energy dissapated as heat

  • Can come from:
    1. a collision 
    2. a current-carrying wire

(among other things)

61

  • Law of Conservation of Energy says...?

  • in an isolated system:
    • energy is ALWAYS CONSERVED
      • e.g., it can be transferred, but never lost

62

  • Define an "Open system" 

  • both mass AND energy
    • ​...can be exchanged with surroundings

63

Define a "Closed system" 

  • Energy, but NOT mass
    • ...can be exchanged with the surroundings

64

  • Define an "Isolated system" 

  • Neither mass NOR energy
    • ​...can be exchanged with the surroundings

65

  • Think of "Work" in what order?
    • ...when it comes to formulas

  1. W=ΔE
  2. W=Fdcosθ

66

  • When I see the following, Ill think "WORK" 
    • 7 things

  1. Change in velocity
  2. Change in height 
  3. Change in positon of masses (or planets in space)
  4. Change in position of a charge
  5. Compression of a spring (PE stored up)
  6. Friction
  7. Air resistance

67

  • Give 2 examples of W=Fdcosθ​
    • aka...give 2 examples of force being applied along a displacement

  1. Pushing a block along a table
  2. An object falling from height
    • height=displacement!
      • Dont forget that!

68

  • What are the ONLY 2 ways energy can be transferred in/out of a system?

  1. Work
  2. Heat (dissapated)

69

  • 1st Law of Thermodynamics
    • Equation=?

ΔE= W + Q

70

  • Work-Energy theorem
    • What should you focus on instead?

  • If Fnet does work on a rigid object:
    •  the work done on that object is equal to:
      • the change in KE of the object
  • Focus on W=ΔE
    • correct use of this negates need to use work-energy theorem

71