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Physics > Topic 5 - Forces, Density and Pressure > Flashcards

Topic 5 - Forces, Density and Pressure Flashcards

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1
Q

Forces

A

actions upon an object that results in an interaction between objects.

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2
Q

Common type of forces. ( 6 )

A
  • Gravitational forces
  • Electrival forces
  • Magnetic forces
  • Frictional forces
  • Drag forces / viscous drag
  • Upthrust force / Buoyant force
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3
Q

Gravitational Force

A

Region where mass experience a force in gravitational field.

  • acts on all masses
  • weakest force
  • field lines are directed towards centre of m
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4
Q

Electrical Force

A

attractive and repulsive interactions that acts on all charged particles

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5
Q

Magnetic Forces

A

acts on magnetic materials / moving charges

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6
Q

Frictional Forces

A

forces which opposes motion that are in contact with each other

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7
Q

Drag force / Viscous drag

A

forces that oppose / prevent motion

  • found in fluids
  • directly proportional with speed
  • also known as air resistance
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8
Q

Upthrust / Buoyant Force

A

vertically acting upwards force on an object partially or fully immersed in fluid due to difference in pressure of fluid

• bottom pressure - top pressure

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9
Q

Terminal velocity

A

Maximum constant velocity when an object is in motion in a fluid / resisting medium and net force is zero.

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10
Q

How different masses varies the terminal velocity?

A
  • higher mass - higher terminal velocity
  • higher mass requires a larger air resistance to balance out the weight of the object
  • higher velocity is needed to gain a larger air resistance
  • hence results in a higher terminal velocity
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11
Q

How energy is conserved in free fall at terminal velocity?

A
  • Object experiences loss in GPE
  • No gain in kinetic energy (constant velocity)
  • Energy is used to do work against air resistance
  • Heat increases - thermal vibration also increases
  • Energy converted to internal energy, increase in internal energy
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12
Q

Centre of gravity

A

(def.) a point where the whole weight / gravity is considered to act, regardless of its orientation.

• uniform shape
- at the geometrical centre

• non-uniform shape
- towards higher mass

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13
Q

Pivot point

A
  • stationary point

* if centre of g > pivot point, object will topples.

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14
Q

Moment of a force

A

(def.) Turning effect of a force

Product of force and the perpendicular distance of pivot to the line action of force

  • M = F x d
  • clockwise & anti clockwise rotation
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15
Q

System in equilibrium

A

TRANSLATIONAL EQUILIBRIUM
• Sum of forces in any direction = 0

ROTATIONAL EQUILIBRIUM
• Sum of moments about any point = 0

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16
Q

Principle of Moments

A

(def.) for an object to be in equilibrium, the sum of moments about any point must be zero

enables us to :
• check whether object will rotate / remains balanced

• calculate unknown force or distance if the object is balanced

17
Q

Common point

A

Intersection points of all forces so that the sum of moments at this point is zero

18
Q

Couples

A

(def.) a pair of equal and oppositely directed paralled forces whose line of action does not coincide.

19
Q

Torque

A

(def. ) turning effect or moment of a couple
(def. ) product of one of the forces with the perpendicular distance between two forces

Torque = F (d1 + d2)

20
Q

Difference in moment and torque

A

Moment
• turning effect of ONE force
• affected by the perpendicular distance of force from PIVOT

Torque
• turning effect of a COUPLE
• affected by the perpendicular distance BETWEEN TWO FORCES

21
Q

Density

A

(def.) mass per unit volume

• constant for :

  • solid
  • liquid that is not compressed

• not constant if
- there’s change in T / V

22
Q

Pressure

A

(scalar quantity)

(def.) Force acting normally per unit surface area

23
Q

Pressure in liquid

A
  • increases the with depth below its surface
  • equal in all directions at the same depth
  • proportional to the density
  • depends on height of liquid only

P = pgh

24
Q

Pressure in gas

A

due to collision between particles and the wall of container
• change in momentum (N2L)
• impulses
• impulsive force is exerted on the wall (N3L)
• gas pressure produced

25
Q

Type of meters

  • Barometer
  • Manometer
A

Barometer : determines Patm

Manometer : determines Pgas
also known as U-tube

Physics (4 decks)

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