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Physics > Motion > Flashcards

Motion Flashcards

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1
Q

what is instantaneous speed

A

it is the speed of the car over a very short interval of time.

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2
Q

How do you calculate instantaneous speed

A

drawing a tangent to the graph and calculate the gradient of the tangent

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3
Q

What does this graph imply

A

A) stationary object
B) constant + speed
C) constant - speed
D) changing speed, slow to fast
E) changing speed, fast to slow
F) constant speed

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4
Q

what is the gradient of a distance-time graph?

A

∆d / ∆t = speed

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5
Q

what do displacement-time graphs represent

A

the gradient represents the velocity of an object.

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6
Q

what is the definition of velocity

A

it is the rate of change of displacement per unit time

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7
Q

What is the definition of speed

A

it is the rate of change of distance per unit time

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8
Q

what is the formula and units for acceleration

A

a = ∆v / ∆t units: ms-2

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9
Q

What is the gradient of a velocity-time graph?

A

∆v / ∆t = a

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10
Q

what do these velocity-time graphs represent

A
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11
Q

What does the AREA of a velocity-time graph represent?

A

ms-1 x s = m

from v x t = s

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12
Q

define stopping distance

A

it is the total distance travelled from when the driver first sees a reason to stop, to when the vehicle stops

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13
Q

what are the two components of stopping distance

A

thinking distance + braking distance = stopping distance

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14
Q

define thinking distance

A

the distance travelled between the moment when you first see a reason to stop, to the moment when you use the brake.

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15
Q

define braking distance

A

the distance travelled from the time the brake is applied until the vehicle stops

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16
Q

what is the formula for thinking distance?

A

thinking distance = speed x reaction time

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17
Q

when is an object said to be in free fall?

A

when an object is accelerating under gravity, with no other force acting on it

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18
Q

what is implied when an object is thrown

A
  • the vertical velocity changes due to gravity
  • horizontal velocity remains constant
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19
Q

why does the horizontal velocity of the projectile remain constant

A

the acceleration of free fall is vertically downwards, the component of this acceleration in the horizontal direction is 0

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20
Q

how can we calculate the actual velocity of a projectile

A
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21
Q

when an object is fired at an angle θ how can the motion be analysed

A

splitting the force into components

vx= v(cos(θ))

vy= v(sin(θ))

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22
Q

how can we use an electromagnet and trapdoor to calculate g

A
  • an electromagnet holds a small steel ball above a trapdoor
  • when current is switched off, a timer is triggered,
  • the ball falls
  • when it hits the trapdoor, the electrical contact is broken and the timer stops.
    • calculate g from height and time taken
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23
Q

example of electromagnet and trapdoor practical

A
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24
Q

how can we use Light Gates to calculate g

A
  • two light beams, one above the other, with detectors connected to a timer
  • when the ball falls through the first beam, it interrupts light and timer starts
    • when the ball falls through the second a known distance the timer stops
25
Q

how can we use pictures to calculate g

A
  • a steel ball is dropped from test next to a metre rule, its fall is recorded on video
  • the position of the ball at regular intervals is then determined by examine the recording
26
Q

example of using pictures to calculate g

A
27
Q

define weight

A

the gravitational force acting on an object through its centre of mass

28
Q

define drag

A

frictional force that opposes the motion of the object in fluid

  • speed ∝ drag2
    • increased cross sectional area increases drag
29
Q

define upthrust

A

an upward buoyancy force acting on an object when it is in a liquid

30
Q

representing an object on a slope

A
31
Q

terminal velocity

A

when the drag force on an object is equal and opposite to the weight of the object, there is no resultant force and therefore the speed remains constant

32
Q

define moment

A

the moment of a force is the turning effect of a force about some axis or point

  • moment = force x perpendicular distance of the line of action of the force or point of rotation
    • moment = Fx
33
Q

principle of moments

A

for a body in rotational equilibrium, the sum of the anticlockwise moments is equal to the sum of clockwise moments about the same point

34
Q

define couple

A

two forces must be parallel and along different lines in the opposite direction

35
Q

define torque

A

the moment of a couple is known as a toque it is defined as

  • torque of a couple = one of the forces x perpendicular separation between the forces = Fd
36
Q

define pressure

A

the normal force exerted per unit cross-sectional area

  • p = F/A
  • calculate pressure in liquids
  • p(ressure) = hpg
  • h - height of the liquid column
  • p - density
    • g - gravity
37
Q

archimedes principle

A

the upthrust exerted on a body immersed in a fluid whether fully or partially submerged is equal to the weight of the fluid that the body displaces

38
Q

upthrust formula

A

upthrust = Axpg

A - area

x - depth

p - density

g - gravity

39
Q

what is work done

A

work done = force x distance moved in the direction of the force

W = Fx

40
Q

principle of conservation of energy

A

the total energy of a closed system remains constant: energy can never be created or destroyed, but it can be transferred from one form to another

41
Q

energy exchange

A

Ek = ½mv2

GPE Ep = mgh

mgh = ½mv2

gh = ½v2

42
Q

define power

A

power is the rate of work done

p = w/t

p- power

w - work done

t - time

43
Q

power and motion

A
  • a constant force F moves the car a distance x in a time t
  • work done by the force W = Fx
  • P= w/t = Fx/t
  • (x/t) = velocity
    • P = Fv
44
Q

efficiency formula

A

efficiency = ( useful output energy / total output energy ) x 100

45
Q

tensile and compressive forces

A
  • forces that produce extension are known as tensile forces
  • forces that shorten an object are known as compressive forces
  • a helical spring undergoes tensile deformation when tensile forces are exerted
    • similarly compressive deformation occurs when compressive forces are exerted
46
Q

hookes law

A
  • the extension of the spring is directly proportional to the force applied as long as the elastic limit of the spring is not exceeded
  • F = kx
    • k - force constant which is a measure of the stiffness of a spring
47
Q

describe the force extension graph

A
  • straight line from the origina up to the elastic limit (A)
  • in this region it undergoes elastic deformation, will therefore return to its original length when the force is removed
  • beyond A is plastic deformation: permanent structural changes to the spring occur and doesnt return to its original state
  • area under graph = work done
48
Q

elastic potential energy

A

E = ½Fx = ½(kx) * x

F - force producing an extension x

E = ½kx2

49
Q

tensile stress

A
  • defined as the force applied per unit cross-sectional area of the wire
  • tensile stress = force/cross-sectional area
    • σ = F/A
50
Q

tensile strain

A

defined as the fractional change in the original length of the wire

tensile strain = extension/original length

Ɛ = x/L

51
Q
A
  • stress ∝ strain from the origin to P, the limit of proportionality
  • E represents the elastic limit
  • elastic deformation occurs up to the elastic limit and plastic deformation beyond that
  • y1 and y2 are upper and lower yield points ,where material extends rapidly
    • UTS , ultimate tensile strength is the maximum stress that a material can withstand when being stretched before it breaks
52
Q

young modulus

A

the ratio of stress to strain for a particular material is a constant and is known as its young modulus, E.

young modulus = tensile stress/ tensile strain

E = σ / Ɛ

53
Q

newtons first law

A

an object will remain at rest or continue to move with constant velocity unless acted upon by a resultant force.

54
Q

newtons third law of motion

A

when two objects interact, they exert equal and opposite forces on each other

55
Q

momentum

A

product of mass and velocity

p = mv

56
Q

principle of conservation of momentum

A

for a system of interacting objects, the total momentum in a specified direction remains constant, as long as no external forces act on the system

57
Q

what is the difference between perfectly elastic and inelastic collisions

A
58
Q

newtons second law

A

the net force acting on an object is directly proportional to the rate of change of its momentum and is in the same direction

F = P/t

F is the net force, P is the change in momentum over time interval t

59
Q

F = ma for momentum

A
  • F = ma
  • a = (v-u)/t
  • F = m(v-u)/t
  • F = (mv-mu)/t
    • F = p/t

Physics (12 decks)

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