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aqa a level physics > mechanics > Flashcards

mechanics Flashcards

1
Q

define scalar quantity
give three examples

A

has no direction, only magnitude
mass, length,distance

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2
Q

define vector quantity
give three examples

A

has both magnitude and size
displacement, velocity, acceleration

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3
Q

describe how you would find the resultant vector of two vectors

A

scale drawing
tip-to-tail
measure missing side of triangle for resultant vector

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4
Q

describe how you would resolve a vector

A

Vx = Vcosθ
Vy = Vsinθ

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5
Q

what is a free-body force diagram

A

shows a single body on its own
shows all the forces acting on the body
arrows

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6
Q

what does it mean to say an object is in equilibrium

A

all forces acting on it are balanced and cancel each other out
no resultant force on the object

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7
Q

are objects at equilibrium always at rest

A

no, can be moving at constant velocity too

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8
Q

forces acting on an object in equilibrium have what property when drawn to scale

A

tip-to-tail
form a closed loop

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9
Q

how would you investigate equilibrium **

A

using a force board
when ring at the centre of the board, equilibrium

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10
Q

what is the mass of an object

A

a measure of the matter in the object
Kg
mass remains constant no matter the gravitational field

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11
Q

what is inertia

A

the resistance to a change in velocity

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12
Q

what does a greater mass mean

A

the greater its resistance to a change in velocity (it’s inertia)

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13
Q

what is weight

A

a force
N
experienced by a mass due to a gravitational field

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14
Q

Weight {}

A

W =mg

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15
Q

approximate value for gravity on the moon

A

1.6NKg^-1

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16
Q

what are the units for gravitational field strength

A

NKg^-1

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17
Q

what is a moment

A

the turning effect of a force around a turning point
force * perpendicular distance from the line of action of the force to the point

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18
Q

moment {}

A

M = Fd
Nm = N * m

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19
Q

what does the principle of moments state

A

for a body to be in equilibrium the sum of the clockwise moments must equal the sum of the anticlockwise moments about any point

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20
Q

if the moments on an object aren’t balanced what happens to the object

A

it explodes!
just kidding.
it will turn

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21
Q

what is a lever

A

where an effort force acts upon a load force by means of a rigid object rotating about a pivot

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22
Q

why are levers useful

A

less force is needed for the same amount
since they increase the distance from the pivot at which force is applied
useful in situations where a large turning effect is needed ( spanners, wheelbarrows ect.)

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23
Q

what is a couple

A

pair of forces of equal size which act parallel to each other in opposite directions
doesn’t cause any resultant force, produces a turning effect

d is the full distance
F is one of the F’s

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24
Q

what is the centre of mass

A

the single point through which you can consider the whole weight of an object to act

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25
Q

how can you find the centre of mass of an object

A

hang the object freely from a point
draw a vertical line downwards from the point of suspension, use a plum bob to get the line completely vertical
hang the object from a different point
draw another line
where the lines cross = centre of mass

26
Q

when would an object topple over

A

if the line action of its weight falls outside it’s base area
since a resultant moment occurs which provides a turning force

27
Q

describe a stable object

A

will have a low centre of mass
will have a wide base area

28
Q

describe how forces act on supports

A

force acting on each support won’t be the same
the closer to the centre of mass the support is, the stronger the force acting on the support

principle of moments

29
Q

what is speed

A

how fast something is moving regardless of direction

30
Q

what is displacement

A

how far an object’s travelled from it’s starting point in a given direction

31
Q

what is velocity

A

the rate of change of an object’s displacement

32
Q

what is acceleration

A

the rate of change of an object’s velocity

33
Q

state the 4 main suvat equations

A

v = u + at
s = ut + 1/2at^2
v^2 = u^2 + 2as
s = (u+v)/2 * t

34
Q

when are the suvat equations used

A

when acceleration is constant

35
Q

what does the gradient of a displacement-time graph show

A

velocity

36
Q

if the gradient of a displacement-time graph isn’t constant ( a curve ) what does it mean

A

the object is accelerating
the velocity is constantly changing

37
Q

what is an object’s instantaneous velocity

how do you find it on a graph

A

it’s velocity at a particular moment in time
tangent to the curve at that point

38
Q

what is the average velocity

A

total displacement / total time

39
Q

what is the gradient on a velocity-time graph

A

acceleration

40
Q

what does uniform acceleration look like on a graph

A

straight line
steeper gradient - greater acceleration

41
Q

what does the area under a velocity-time graph represent

speed-time

A

displacement of the object

distance travelled by the object

42
Q

how is non-uniform acceleration shown on a graph

A

non-constant gradient
curve on velocity-time graph

43
Q

main advantages of data loggers

A

data more accurate
human reaction times don’t have to be accounted for

much higher sampling rate (more reading can be taken per second)

data can be processed and displayed in real time

44
Q

what is freefall

A

when there’s gravity acting on an object and nothing else
‘motion of an object undergoing acceleration g’

45
Q

who’s this galileo guy

A

he conspired that all objects fall at the same rate
free-falling objects fell too quickly for him to be able to take any accurate measurements, air resistance always came in the way too
he measured time it took for a ball to roll down a smooth slope
observed the distance travelled was proportional to the square of the time taken
accelerating at a constant rate

46
Q

determining g using free fall

A

set up electromagnet in a circuit with switch
ball bearing
measure height h
release ball bearing and simultaneously begin the timer
when ball bearing hits trapdoor stop the timer
repeat few times to calculate an average
repeat for different heights h
plot a graph of height against s^2
gradient = 1/2 g

47
Q

what are common sources of error in the determining g required practical

A

random error - uncertainty of using rulers
small and heavy ball bearing - air resistance can be assumed to be negligible
stopwatch - reaction times can heavily skew results

48
Q

what is a projectile

A

an object given initial velocity and then left to move freely under gravity
horizontal and vertical components are independent of one another

49
Q

why do projectiles follow a curve

A

horizontal velocity remains constant
vertical velocity affected by acceleration due to gravity , ‘g’

50
Q

air resistance in projectile motion

A

causes a drag force that acts in opposite direction to motion and affects trajectory of a projectile
vertical component - drag affects the maximum height the projectile will reach

51
Q

a block is at rest on the floor
describe the forces acting up on it

A

weight - force of block on floor due to gravity
support force - force on block due to floor

52
Q

how can you calculate the weight of a beam/ metre ruler

A

weight acts through centre of mass
so at 0.5m
then apply principle of moments

53
Q

upwards force =

A

downwards force

54
Q

two support problem

A

if centre of mass is midway between beam, weight is shared equally between the two supports
if not, ~~↓ = ~~~~~~~~↑

55
Q

what does it mean to say a body is in stable equilibrium

why?

A

is the body is suspended and then released it returns to it’s equilibrium position

the line of action of weight of the object feels the need to pass through the point of support
when the object is at rest
the centre of mass of an object is directly below its point of support

56
Q

what is tilting

A

when an object at rest on a surface is acted on by a force that raises it up on one side
Fd > weight*(base/2)
clockwise > anticlockwise

57
Q

what it toppling

A

if tilted too far an object will topple
line of action of the weight passes beyond the pivot

58
Q

2 conditions for equilibrium

A

resultant force must be zero
principle of moments must apply. turning effects balance out

59
Q

as speed increases how is air resistance affected

A

air resistance increases
proportional to square of speed

60
Q

what is meant by terminal velocity

A

when the forces acting on a falling object become balanced
zero acceleration
falling at a constant velocity

aqa a level physics (10 decks)

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