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Physics > 1) Circular Motion > Flashcards

1) Circular Motion Flashcards

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1
Q

Rotation of a rigid body around an axis

A
  • all points of the body perform circular motion
  • the circular trajectories lie in a parallel line
  • the centre of the circle lies on the axis of rotation
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2
Q

Equation of circular motion

A

Alpha= f(t)

DRAWING

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3
Q

Angular velocity equation and angular acceleration equation

A

Angular velocity

W= d(alpha)/ dt

Angular acceleration

E= Dw/dt

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4
Q

Distance, velocity and acceleration

A

Distance travelled
S=r(alpha)

Velocity
V=rw

Acceleration
a_t=rE

DRAWING

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5
Q

Centripetal force

A

For uniform rotation of a particle with mass M a force of constant magnitude is needed pointing towards the centre or rotation = F_c

F_c changes the direction of velocity and gives rise to centripetal acceleration a_c

F_c= m x a_c

a_c= rw^2

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6
Q

Torque (moment)

A

Torque(M) exerted by F relative to the axis of rotation

M= F r sinB
B= Vector between F and r

B and M can be negative or positive depending on direction of rotation

M can change the magnitude of velocity

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7
Q

Separation of components in heterogeneous system

A

Place heterogeneous system in field of appropriate force

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8
Q

Sedimentation

A

Separation of components of a heterogeneous system by gravity.

F_g=mg=pVg

F_a= p_sVg

F=(p-p_s) Vg

DRAWING

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9
Q

Sedimentation 2

A

When P = Ps the heterogeneous system can’t be separated by sedimentation

DRAWINGS

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10
Q

Centrifugation

A

Gravitational forces are weak and sedimentation only takes place very slowly or is impossible bc of diffusion (Brownian motion)

Centrifugation is the separation of the components of a heterogeneous system by the centripetal force

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11
Q

Centrifugation 2

A

DRAWING

F= (P-Ps) Va_c

F=(P-P_s) Vrw^2

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12
Q

Separation of components in heterogeneous system

A

Place heterogeneous system in field of appropriate force

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13
Q

Sedimentation

A

Separation of components of a heterogeneous system by gravity.

F_g=mg=pVg

F_a= p_sVg

F=(p-p_s) Vg

DRAWING

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14
Q

Sedimentation 2

A

When P = Ps the heterogeneous system can’t be separated by sedimentation

DRAWINGS

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15
Q

Centrifugation

A

Gravitational forces are weak and sedimentation only takes place very slowly or is impossible bc of diffusion (Brownian motion)

Centrifugation is the separation of the components of a heterogeneous system by the centripetal force

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16
Q

Centrifugation 2

A

DRAWING

F= (P-Ps) Va_c

F=(P-P_s) Vrw^2

17
Q

Centrifugation 3

A

When p =p_s then the separation of heterogenous systems using centrifugation will not occur

DRAWING

17
Q

Sedimentation rate and duration of sedimentation

A

All moving particles experience drag

F_d=Fv
F= friction
V= velocity

DRAWING

18
Q

Sedimentation rate and duration of centrifugation 2

A

Particles with constant velocity:

Fv=(p-p_s)vrw^2

Terminal velocity:

V=(p-p_s)vrw^2/F

The centrifugation time is sufficient for even the most distant particles to reach the end of the tube

19
Q

Sedimentation rate

A

This is proportional to

P-P_s
r
The square of W
The reciprocal of f

20
Q

Sedimentation coefficient and relative centrifugal force RCF

A

Sedimentation coefficient:

S=v/a_c = v(p-p_s)/f

RCF:

G= a_c/g = rw^2/g

21
Q

Centrifuge and main parts

A

An instrument that separates heterogenous systems by rotation

Main parts

  • axis
  • rotor (fixed angle rotor)
  • motor (swinging bucket rotor)
22
Q

Rotor balancing

A

The overall radial force has to be very small otherwise the centrifuge could be damaged

  • ensure that tubes are placed symmetrically to distribute weight evenly
  • the masses of the tubes have to be equal
23
Q

Types of centrifuges

A

Preparative
- used for the isolation of cell membranes, organelles and cells

Analytical
-used for the investigation of biological macromolecules

24
Q

Centrifugal methods

Differential centrifugation

A
  • suspension of 2 solid fractions

Centrifugation at low speed will isolate fractions with higher sedimentation

Centrifugation at high speed will seaports second fraction from solvent

25
Q

Centrifugation methods

Zone centrifugation

A

-mixture of 3 solid fractions

The density of solvent is growing from top to bottom

The mixture of particles is placed at the top

Centrifugation results in the grouping of particles according to sedimentation rate

26
Q

Centrifugation methods

Isopycnic centrifugation

A

-mixture of 3 solid fractions

The sample is stirred this produces a density gradient during centrifugation

The particles move to the place where the density of the solvent is equal to their own density and stop

Physics (11 decks)

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