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Physics > Dynamics > Flashcards

Dynamics Flashcards

1
Q

what is dynamics?

A

Dynamics considers the forces that affect the motion of moving objects and systems.

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2
Q

balanced forces do/do not cause a change in the motion.

A

does not

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3
Q

what are the forces that act on an object when net force = 0?

A

gravitational force and normal force.

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4
Q

force is _______ quantity.

A

vector

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5
Q

what is net force?

A

vector sum of all the forces acting on an object.

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6
Q

the force of an object = 0 N then the force is ___________.

A

balanced

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7
Q

what is inertia?

A

the tendency of an object in motion to stay in uniform velocity, and objects at rest to stay at rest unless acted upon by an external force to change its motion or direction.

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8
Q

what is force?

A

vector quantity which changes or tends to change the state of a body, start or stop its motion speed it up or slow it down & can change the direction of force and shape of an object.

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9
Q

state the law of inertia?

A

an object at rest will remain at rest, and an object in motion will continue moving with a constant velocity, unless acted upon by an external unbalanced force.

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10
Q

what does net force tell us?

A

whether the forces on the object are balanced or not balanced.

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11
Q

for forces to be balanced, it should ____________.

A

be equal in MAGNITUDE
be opposite in DIRECTION
these cancel the effect and 0 net force.

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12
Q

Δv=0 then

A

a = 0
F net =0

no acceleration = no motion

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13
Q

inertia is _________ ∝ to the mass of an object.

A

directly

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14
Q

inertia is _______ ∝ to the acceleration.

A

inversely
more inertia (mass) less acceleration.

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15
Q

The measure of inertia is _______________.

A

the mass of the body

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16
Q

a is __________ proportional to the F net.

A

directly

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17
Q

greater the unbalanced net force, the ______
the acceleration.

A

greater

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18
Q

greater the mass of an object, the __________ the acceleration.

A

smaller

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19
Q

a is ____________ proportional to the mass of an object

A

inversely

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20
Q

state Newton’s 2nd law of motion?

A

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

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21
Q

Newton is the unit of _______.

A

force (N)

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22
Q

1N =

A

1kg x 1m/s2
OR
kg m/s2

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23
Q

what is matter?
what is mass?

A

anything that has mass and occupies volume
amount of matter an object contains.

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24
Q

what is weight?

A

gravitational force acting on a mass.

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25
Q

W=

A

m x g

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26
Q

W is measured in ________.

A

Newtons

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27
Q

object in uniform motion has net force of ________.

A

0

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28
Q

net force =?

A

applied force - frictional force

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29
Q

the force exerted by the bullet on the gun is written as ______________

A

Fbg

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30
Q

why do feel pain when punching a wall or falling on the ground?

A

because we also get force on to our hands and legs as a reaction force.

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31
Q

what is tension?

A

the pulling force exerted by a stretched rope or sting on an object to which it’s attached.

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32
Q

tension is a _______ force.

A

only pulling

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33
Q

In Figure A, in what direction the weight and tension is?
what causes it? what can we conclude?

A

the block pulls the string downward by its weight, this causes T in the string. The tension is acting upward.
As the block is at rest, therefore the weight of the block must be balanced by the upwards T in the string.
Thus we conclude that T must be = and opposite to the weight of the block.

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34
Q

inextensible?

A

unable to be stretched

35
Q

in Atwood machine what is the formula of a and g

A

a= m1 - m2 / m1+ m2 g
g = 2m1 + m2 / m1 - m2 a

36
Q

tension formula in Atwood machine?

A

2m1 m2/ m1 + m2 g

37
Q

in figure 3 of frictionless pulley what are the forces acting on body B and body A?
why is the tension same for both bodies?
what is the formula for a and T?

A

frictionless pulley

38
Q

diffusion can happen in gas and liquids. T/F

A

True

39
Q

what is momentum?

A

quantity of the motion it possesses due to its mass and velocity.

Quanitity of motion: It’s a measure of how much a moving object resists changes in its motion (due to its mass) and how fast it’s moving (due to its velocity).
The larger the mass or the faster the velocity of an object, the greater its momentum.

40
Q

SI unit of momentum? symbol? vector or scalar?

A

kg/ms or Ns
P
vector

41
Q

momentum is a ___________ quantity that points in which direction?

A

vector
in the same direction as velocity.

42
Q

state the formula of momentum in terms of force and state 2nd law of motion?

A

change in momentum/t=F
when a force acts on a body, it produces acceleration in the body and will be equal to the rate of change of momentum of the body.

43
Q

derive that rate of change of momentum= force in 2 ways.

A

pg 68
pg 73

44
Q

When does momentum remain constant?

A

If no unbalanced or external net force acts on a system then according eq. 3.14 its momentum remains constant.

44
Q

define isolated system?

A

group of bodies, under study separated by a boundary is called a system. If the net external force on the system is 0, it is termed as isolated system.

45
Q

State the formula for conservation of momentum?

A

m1u1 + m2u2 = m1v1 + m2v2
u = initial velocity

46
Q

How should we know that the the m2 ball will move in what direction after collision? and why?

A

We will solve for it using formula of law of conservation of momentum and if the answer is + it will move in the same direction the other m1 ball moves and if - then vice versa. Because the greater velocity influence the direction of smaller velocity.

47
Q

Derive the formula for the law of conservation of momentum?

A

Page 69

48
Q

What is friction?

A

the force that opposes the motion of moving object.

49
Q

The greater the pressing force, _________ will be the force of friction. why?

A

Greater
because the weight of the object (or pressing force) is more and they’re pressed harder together so the interlocking between irregularities is more.

50
Q

what are the factors that affect friction?

A

nature of both surfaces
force with which the two surfaces are pressed together.

51
Q

friction symbol? unit? quantity? for which matter it acts?

A

f
N
vector (cz it’s a force)
solids, liquids and gases.

52
Q

why is friction caused?

A

irregularities on the 2 surfaces in contact.
more irregularities ,more friction. cz they interlock more.

53
Q

what is force of limiting friction?

A

the maximum force of friction that can exist between the two objects before one of them starts sliding to the other. It opposes the initiation of motion.
aka Static Friction.
FMIGTN

54
Q

what is coefficient of friction?

A

the ratio between the force of limiting friction and the normal force is constant. This constant is called coefficient of friction.

normal force= reaction to weight.

55
Q

mu=

A

Coefficient of Friction (μ) = Force of Limiting Friction / Normal Force

56
Q

F s=

A

F s = μs X R

R= normal force

μs= coefficient of friction

57
Q

what is sliding friction?

A

the resistance created by any two objects when sliding against each other. This friction is defined as the force that is needed to keep a surface sliding along another surface.
aka kinetic friction

58
Q

what is rolling friction?

A

when a body rolls over a surface, the force of friction is called rolling friction.

59
Q

rolling friction is _______ than sliding friction.

A

less
sliding is more.

60
Q

sliding friction is _____ than static friction. why?

A

less
static is more.

61
Q

why does the cyclist need to stop his wheels rolling over to stop?

A

as soon as the brakes are applied, the wheels stop rolling and begin to slide over the road. Since sliding friction is much greater than rolling friction Therefore, the cycle stops very quickly.

62
Q

what are the types of frictional forces?

A

2
static
kinetic (sliding)

63
Q

how to measure force of limiting friction? symbol?

A

fs= mu x N

64
Q

How to measure normal force?

A

N = W= mg

65
Q

why do cars skid?

A

to stop a car quickly, a large force of friction is needed, however, there is a limit to this force of friction that the wheels can provide. So when the brakes are applied strongly the tires lock up and skid due to its large momentum.

66
Q

advantages and disadvantages of friction?

A
67
Q

what are the methods to reduce friction?

A

4
1. Making the sliding surfaces smooth by polishing
2. By applying lubricants to surfaces
3. By using ball bearings this method converts the sliding friction into rolling friction by the use of ball bearings.
4. Streamlining the fast-moving objects, this causes the smooth flow of air and minimizes air resistance at high speeds.

68
Q

what does centripetal & centrifugal mean?

A

centri, “center” petere, “go towards, seek”.
latin centri and fugere meaning “to flee”

69
Q
  1. in uniform circular motion, what is the direction of force?
  2. how can there be force?
  3. where is force in there?
  4. is the body moving at a constant velocity?
A
  1. towards the center
  2. acceleration is there (direction)
  3. in the rope (tension in rope)
    no, constant speed, changing velocity (change in direction)
70
Q

what is the direction of the velocity of the ball at any point?

in uniform circular motion

A

the direction of velocity is perpendicular to the radius. direction of the velocity is along a tangent to the circle
when the string is cut then the direction of that ball will be perpendicular to the radius, when a ball flies off in a straight line, it is tangent to the circle at that point it flies off.

71
Q

what is the direction of acceleration in uniform circular motion?

A

same as force
towards the center (inwards)
centripetal acceleration
the direction of acceleration is always perpendicular to the velocity at that point.
acceleration is always changing the direction of velocity not magnitude of velocity.

72
Q

ac =?

A

v2/r

73
Q

Fc=?

A

m ac
m v2/r

74
Q

ac is ___________ proportional to the radius and velocity?

ac=centripetal acceleration

A

inversely As the radius decreases, the centripetal acceleration increases

directly as the velocity increases, the centripetal acceleration also increases.

75
Q

what is centripetal force and acceleration?

A

A centripetal force is a net force that acts on an object to keep it moving along a circular path.

76
Q

what is centrifugal force?

A

centripetal reaction that pulls the string outward is sometimes called the centrifugal force. It is defined as an apparent force. The apparent outward force has been given a name. This outward tug is called centrifugal force.

77
Q

balanced forces causes _____________.

A

no motion

78
Q

unbalanced forces causes _____________.

A

motion

79
Q

define 1 Newton?

A

the force that produces acceleration of 1 m/s2 in a body of mass 1 kg.

80
Q

state the law of conservation of momentum?

A

the momentum of an isolated system of two or more than two interacting bodies remains constant.

81
Q

velocity time graph for zero, positive, negative, constant, increasing acceleration.

A

zero acceleration= constant velocity

82
Q

final and intital momentum of gun & a bullet? what does the -ve sign inidcate?

A

MV + mv = 0
V=-mv/M
velocity of gun is opposite to the velocity of the bullet ie the gun recoils.

Physics (9 decks)

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