Physics 2 Flashcards
- Think of a “FIELD” as:
- an invisible influence capable of exerting a force on a MASS or CHARGE
- Universal Law of Gravitation (formula)
Fg=Gm1m2/r2
- The Universal Law of Gravitation is true everywhere, but NEAR EARTH’S SURFACE:
- What do we assume?
- What formula can we simplify to?
- Assume g= 10 m/s2
- Simplify to:
- F=mg
- Simplify to:
- 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
- use PEgrav=pgh
- 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!!!
- Friction opposes ____, not ____
SLIDING!
- not motion
- If theres SLIDING, it’s ___ friction
- If NOT, its ___ friction
- sliding= kinetic friction
- not sliding=static friction
- 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
- 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
- Inclined Planes
- Give the equation for:
- Force down an inclined plane
- parallel to the surface
- Force down an inclined plane
- Give the equation for:
F=mgsinθ
- Inclined planes:
-
Normal force on an Inclined Plane
- Equation=?
-
Normal force on an Inclined Plane
Fn=mgcosθ
- Inclined planes:
- Velocity of a particle at the base of an inclined plane
- Equation=?
Vf=√2gh
- Inclined planes
- ACCELERATION down an inclined plane
- Equation=?
a=gsinθ
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Hooke’s Law formula
F=kΔx
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- 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 p_oint
- for ONE trial
-
Difference in displacement
- between TWO trials
- _Displacement from equilibrium p_oint
- 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
- PEelastic
- Definition
- Equation=?
PEelastic=½kΔx2
- PEelastic= PE stored in a compressed spring
- 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
- Kinetic Energy equation=?
KE=½mv2
- Finding how far a spring compresses
- What COMBINATION of formulas would you use?
Set KE equal to PEelastic
- ½mv2 = ½kΔx2
-
ONE CYCLE of a pendulum is?
- (LOTR)
- “There and back again”
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- For a pendulum to exhibit Simple Harmonic Motion (SHM)…
- What value must be LOW?
- Angle of displacement
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Give 3 examples of Simple Harmonic Motion
- Pendulum
- mass on a string
- Things w/ circular motion when viewed from the side
- Ex: Something bobbing up & down in the water
- has a circular motion!
- Ex: Something bobbing up & down in the water
- Waves sloshing back & forth in a container
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-
Simple Harmonic Motion
- Give the Mass on a Spring formula
T=2π√m/k
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-
Simple Harmonic Motion
- Give the pendulum formula
T=2π√L/g
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-
Simple Harmonic Motion
- What is “T?”
- What thing is its inverse?
T=period
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- inverse to frequency
- f=1/T
- Objects at rest are in ___ equilibrium
STATIC equilibrium
- Objects moving at CONSTANT velocity are in ___ equilibrium
DYNAMIC equilibrium
- 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
- Give 3 examples of equilibrium
- Terminal velocity
- mg=Fair
- Constant velocity
- Objects at rest
-
Torque formulas3 variations)
- Break down what each part represents
- T=fl
- T=mgl
-
T=Frsinθ
- l=lever arm
- r=dist b/t force & point of rotation
- 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
- To solve for:
-
fulcrum and boards on strings problems
- Hint: these are in equilibrium
-
fulcrum and boards on strings problems
Set:
-
Tclockwise=Tcounterclockwise
- include ALL torques!
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- 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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- Define:
- systems NOT in equilibrium
- where the object has NON-ZERO ACCELERATION
- 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
- but add “ma” to the “losing side”
You can IGNORE SIGNS (+/-) when you do this method!
- 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
- Down forces always equal to F=mgsinθ
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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”
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)
How many radians per 1 revolution
~6
- 6.28 exactly
How to convert Radians to degrees
- 2π radians/360°
or
- π radians/180°
- An object is in rotational equilibrium IF:
- 2 options…either one or the other
- It is NOT rotating, or
- It is rotating with constant ω (angular velocity)
- Momentum formula=?
p=mv
- 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
- Define “Impulse”
-
change in an object’s momentum
- “Δp”
-
Impulse formula
- 3 variations (in order of how you should think of impulse)
- I=Δp
- I=mΔv
- I=Favgt
- 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
- Elastic vs Inelastic collisions
Elastic Collisions
- p AND KE conserved
Inelastic Collisions
- p conserved ONLY
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- If object is deformed during collision, it was a _____ collision
- inelastic
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- Elastic collisions
- Equation=?
- Hint: What gets conserved during elastic collisions?
½m1v12+ ½m2v22= ½m1v12+ ½m2v22
- p and KE both conserved
- For PERFECTLY elastic collisions, what 2 weird things happen?
- What’s a (albeit imperfect, but close enough) example of this?
-
Speed is conserved
- before AND after collision
- If mass of 2 objects is equal but they have different velocities:
- velocities get exchanged
- in order to conserve momentum (p=mv)
- velocities get exchanged
Think of: BILLIARD BALLS
-
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
- “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
-
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
- Thermal expansion formula
ΔL=αLoΔT
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- Heating solids leads to ___
- Cooling solids leads to ___
- expansion
- shrinkage
- 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
- because of of highly ordered lattice structure of ice
- PEelec
- formula=?
- 2 variations
- PEelec=Kq1q2/r
or
- PEelec=qEd
- PEcapacitor formula=?
- 3 variations
- PEcapac=½QV
- PEcapacitor=½CV2
- PEcapacitor=½Q2/C
-
Internal energy
- definition
- Energy of:
- Internal vibrations &
-
Random motions of:
- molecules and/or
- atoms w/
…in a system
- Heat energy
- Definition
- Where can Heat Energy come from? (2)
=energy dissapated as heat
-
Can come from:
- a collision
- a current-carrying wire
(among other things)
- Law of Conservation of Energy says…?
- in an isolated system:
- energy is *ALWAYS* *CONSERVED*
- e.g., it can be transferred, but never lost
- energy is *ALWAYS* *CONSERVED*
- Define an “Open system”
- both mass AND energy
- …can be exchanged with surroundings
Define a “Closed system”
-
Energy, but NOT mass
- …can be exchanged with the surroundings
- Define an “Isolated system”
-
Neither mass NOR energy
- …can be exchanged with the surroundings
- Think of “Work” in what order?
- …when it comes to formulas
- W=ΔE
- W=Fdcosθ
- When I see the following, Ill think “WORK”
- 7 things
- Change in velocity
- Change in height
- Change in positon of masses (or planets in space)
- Change in position of a charge
- Compression of a spring (PE stored up)
- Friction
- Air resistance
- Give 2 examples of W=Fdcosθ
- aka…give 2 examples of force being applied along a displacement
- Pushing a block along a table
- An object falling from height
- height=displacement!
- Dont forget that!
- height=displacement!
- What are the ONLY 2 ways energy can be transferred in/out of a system?
- Work
- Heat (dissapated)
- 1st Law of Thermodynamics
- Equation=?
ΔE= W + Q
- 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
- the work done on that object is equal to:
- Focus on W=ΔE
- correct use of this negates need to use work-energy theorem