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Phy > Chap 2- forces, moment, pressure > Flashcards

Chap 2- forces, moment, pressure Flashcards

1
Q

Define force

A

a push, pull or twist

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2
Q

What can a force change

A

speed, direction, shape

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3
Q

Which type of quantity are forces

A

vector

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4
Q

What is used to show forces

A

arrow with heads

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5
Q

How does the arrow show force

A
  • arrow size - magnitude (size) of force
  • arrow head - direction of force
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6
Q

Note: Always label your arrows magnitude

A
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7
Q

name the 9 types of forces

A

-friction,
-compression
-tension
-weight
-applied
-air/ water resistance
-magnetic
-electrical
-normal (upthrust, buoyancy for in water)

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8
Q

Name the 6 contact forces

A

-friction
-applied
-compression
-normal
-air/ water resistance
-tension

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9
Q

Name the 3 non contact forces

A

-electrical
-weight
-magnetic

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10
Q

Name 2 types of friction

A

-static
-dynamic

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11
Q

define friction

A

force that opposes one surface moving or tying to move past another (opposes motion)

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12
Q

define static friction

A

force that keeps object at rest

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13
Q

define dynamic friction

A

opposes sliding or rolling motion

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14
Q

When walking on the floor what forces magnitude are equal or not equal to each other

A

-normal = weight
-thrust is more than resisting force (friction and air resistance combined) because the person is able to moving

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15
Q

Why do we not sink into the floor or float

A

because normal force is equal to weight

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16
Q

Which is bigger: static or dynamic friction

A

static friction

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17
Q

Which friction is on a object at rest

A

static

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18
Q

what is resisting force

A

force opposing another force

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19
Q

What is resultant force

A

a single force that can replace all individual forces acting on the object, and have the same effect

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20
Q

How do you find the resultant force

A

-arrows in same direction = add the forces
-arrows in different direction = minus the forces and the greater force will the the resultant force in the greater force direction
-if minus becomes 0, the resultant force is 0 so stationary

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21
Q

Which directions can a force move in

A

North, South, East, West and anywhere in between

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22
Q

What are the effects of friction

A

opposes motion, creates heat

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23
Q

What is the unit for force

A

Newtons (N)

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24
Q

define Newton’s 1 law

A

An object will remain stationery ( at rest) or move in a constant (uniform) speed in a straight line unless a net resultant force acts on it

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25
Q

define Inertia

A

an objects resistance to change in speed and its direction

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26
Q

What is the relationship between Mass and Inertia

A

As mass increase, Inertia increases

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27
Q

What is the effect of increased Inertia

A

greater Inertia, more difficult to move the object when stationary or change its speed or direction when moving

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28
Q

What is the mass of a body

A

measure of Inertia

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29
Q

State Newton’s 3 law

A

for every action, there is an equal and opposite force on it (forces act in pairs)

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30
Q

Define balanced

A

forces in opposite directions that have the same magnitude

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31
Q

how does forces always act in

A

pairs

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32
Q

What does every object with a mass have

A

a gravitational field

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33
Q

an object with a constant speed has what forces that are?

A

forward and backward forces that are balanced

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34
Q

When will there be in unbalanced forces

A

acceleration

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35
Q

define Newton’s 2 law - symbols and words

A

force = mass x acceleration
F = ma

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36
Q

What are the units in Newton’s second law

A

-Force - Newtons (N)
-Mass - Kilograms (Kg)
-Acceleration - ms^-2

37
Q

What is the relationship between force and acceleration

A

as forces increases, acceleration increases
mass is constant

38
Q

What is the relationship between Mass and acceleration

A

as mass increases, acceleration decreases
force is constant

39
Q

Write down the symbols and units for:
-weight
-force
-mass
-velocity
-speed
-acceleration

A

-weight - w, N
-force - F, N
-mass - m, kg
-velocity - v, ms^-1
-speed- s, ms^-1
-acceleration - a, ms^-2

40
Q

define human reaction time

A

time taken for a human reaction

41
Q

When happens when:
-a force is applied to a spring
-the forces is removed from the spring
- keep applying a force on the spring
-stretch the spring too far

A
  • change shape
    -return to original shape
    -keep getting bigger
    -spring expands to a point where it cannot return back to its original shape
42
Q

what are the 2 purposes for springs

A

tension, compression

43
Q

define elastic object

A

an object that returns back to its original shape

44
Q

When drawing graph, where must the line of best fit start from

A

the origin

45
Q

give 3 examples of elastic objects

A

rubber band, spring , sponge

46
Q

Define limit of proportionality

A

-the point beyond which the extension of an elastic object is no longer directly proportional to the force applied to it
-(where it stop being proportional)

47
Q

What is Hooke’s law

A

the extension of a spring is directly proportional to the force applied to it until it exceeds the limit of proportionality

48
Q

define spring constant measure

A

stiffness of the spring

49
Q

what is the relationship between the spring constant and the stiffness of the spring

A

as spring constant increases, stiffness of the spring increases

50
Q

What is the formula for spring extension - symbols and words

A

Force = spring constant x extension of spring
F = kx

51
Q

What are the units in the formula for spring extension

A

-Applied Force = Newtons (N)
-Spring constant = Newtons per meter (Nm^-1)
-extension = meters (m)

52
Q

How do you find the extension of a spring

A

stretched length - original length

53
Q

Give 2 places tension springs are used

A

machines and trampolines
(creates suspension)

54
Q

Give 2 places compression springs are used

A

pens, cell phones

55
Q

define moment

A

turning force

56
Q

which 2 direction can a moment turn into

A

clockwise, anti-clockwise

57
Q

Explain the resultant force in a moment

A

difference between clockwise and anti-clockwise moments, needs to have a magnitude and direction (unbalanced)

58
Q

define Equilibrium in a moment

A

the clockwise and anti-clockwise moments are equal (balanced) = resultant force and resultant moment are 0

59
Q

define pivot

A

turning point (needs to touch the surface)

60
Q

where is the force applied and which direction on a beam with pivot

A

at the end of the beam, down

61
Q

How are the arrows in a moment drawn

A

draw the arrow as the size of the force and the direction of the force (curved)

62
Q

What is the formula for moment - symbols and words

A

moment = force x perpendicular distance from the pivot
m = Fd

63
Q

What are the units for the formula for moment

A

-moment - Newtons x meters (Nm)
-Force - Newtons (N)
-distance - Meters (m)

64
Q

Define distance in moment

A

distance has to be perpendicular to pivot from the force

65
Q

Define center of gravity

A

point where whole weight of object seems to act

66
Q

what is the requirement for a regular shape

A

needs at least 1 line of symmetry

67
Q

define a regular shape

A

has 1 or more lines of symmetry

68
Q

How do you find centre of gravity for regular shapes

A

do lines of symmetry and the middle where the lines intersect is the center of gravity

69
Q

What must you do when you draw the lines of symmetry and find the centre of gravity

A

label them

70
Q

How do you find center of gravity for irregular shapes

A

-on a retort stand place the cork
-poke a hold into the shape and place it hanging freely using a nail
-place a bob on the cork and draw a line on following the string of the bob on the shape. Repeat 3 time, each time poking holes in different places

71
Q

How is an object stable

A

the center of gravity is within the base of the object

72
Q

define stability

A

how likely an object will fall when disturbed

73
Q

relationship between the base and stability

A

-bigger the base, more stability

74
Q

relationship btw center of gravity and stability

A

-higher center of gravity, less stability

75
Q

Name 3 types of equilibrium and explain them

A

-stable equilibrium - object returns to its original equilibrium position
-unstable equilibrium- object does not return to its original equilibrium position
-Neutral equilibrium - object remains in displaced position

76
Q

what is the difference between w = fd and m = fd

A

w = fd - d- distance + displacement
m = fd - d - physical distance

77
Q

what are equal when balanced (moment)

A

anti - clockwise moment = clockwise moment

78
Q

what is pressure

A

force per unit area

79
Q

what is the equation for pressure in solid

A

p = F / A
pressure = force / area

80
Q

what is the units for pressure in solids

A

p= Pa (pascal) / Nm ^-2 / Ncm ^-2
F= N
A = m^2

81
Q

note: 10000cm ^2 = 1m ^2

A
82
Q

Note: be careful with the unit for area

A
83
Q

as area increases, pressure?

A

decreases

84
Q

as force increased, pressue?

A

increases

85
Q

what is the equation for pressure in liquids

A

p = hpg
pressure = height x density x gravity

86
Q

what is the units for pressure in liquids

A

p = Pa
h = m
p = density
g =NKg ^-1 (9.8)

87
Q

how does pressure act at 1 depth in liquids

A

equally in all directions

88
Q

what does pressure not depend on

A

size and shape of the container

Phy (11 decks)

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