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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
how can you find the centre of mass of an object
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
when would an object topple over
if the line action of its weight falls outside it's base area since a resultant moment occurs which provides a turning force
27
describe a stable object
will have a low centre of mass will have a wide base area
28
describe how forces act on supports
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
what is speed
how fast something is moving regardless of direction
30
what is displacement
how far an object's travelled from it's starting point in a given direction
31
what is velocity
the rate of change of an object's displacement
32
what is acceleration
the rate of change of an object's velocity
33
state the 4 main suvat equations
v = u + at s = ut + 1/2at^2 v^2 = u^2 + 2as s = (u+v)/2 * t
34
when are the suvat equations used
when acceleration is constant
35
what does the gradient of a displacement-time graph show
velocity
36
if the gradient of a displacement-time graph isn't constant ( a curve ) what does it mean
the object is accelerating the velocity is constantly changing
37
what is an object's instantaneous velocity how do you find it on a graph
it's velocity at a particular moment in time tangent to the curve at that point
38
what is the average velocity
total displacement / total time
39
what is the gradient on a velocity-time graph
acceleration
40
what does uniform acceleration look like on a graph
straight line steeper gradient - greater acceleration
41
what does the area under a velocity-time graph represent speed-time
displacement of the object distance travelled by the object
42
how is non-uniform acceleration shown on a graph
non-constant gradient curve on velocity-time graph
43
main advantages of data loggers
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
what is freefall
when there's gravity acting on an object and nothing else 'motion of an object undergoing acceleration g'
45
who's this galileo guy
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
determining g using free fall
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
what are common sources of error in the determining g required practical
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
what is a projectile
an object given initial velocity and then left to move freely under gravity horizontal and vertical components are independent of one another
49
why do projectiles follow a curve
horizontal velocity remains constant vertical velocity affected by acceleration due to gravity , 'g'
50
air resistance in projectile motion
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
a block is at rest on the floor describe the forces acting up on it
weight - force of block on floor due to gravity support force - force on block due to floor
52
how can you calculate the weight of a beam/ metre ruler
weight acts through centre of mass so at 0.5m then apply principle of moments
53
upwards force =
downwards force
54
two support problem
if centre of mass is midway between beam, weight is shared equally between the two supports if not, ~~↓ = ~~~~~~~~↑
55
what does it mean to say a body is in stable equilibrium why?
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
what is tilting
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
what it toppling
if tilted too far an object will topple line of action of the weight passes beyond the pivot
58
2 conditions for equilibrium
resultant force must be zero principle of moments must apply. turning effects balance out
59
as speed increases how is air resistance affected
air resistance increases proportional to square of speed
60
what is meant by terminal velocity
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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