Mechanics experiments Flashcards
(77 cards)
1
Q
Boyle’s Law - method
A
- connect air pump to oil reservoir of Boyle’s Law apparatus
- Pump air in until pressure gauge shows its at max. Close + remove tap
- Leave apparatus for a few mins to allow temp to stabilise + not affect results
- Read pressure off Bourdon gauge
- Measure volume of liquid using scale on apparatus
- Open tap to release some air, then close. Leave for a few mins, then record pressure + volume again
- repeat a no. of times until pressure goes back to atmospheric pressure
2
Q
Boyle’s Law - graph
A
x-axis: 1/V (1/cm³)
y-axis: Pressure (Pa x 10⁵)
3
Q
Boyle’s Law - how graph verifies Boyle’s law
A
straight line through origin verifies p ∝ 1/V
4
Q
Boyle’s Law - use graph to estimate pressure of gas at volume of ___
A
- Find 1/V first as graph is in 1/V
- Use graph and make sure to write x kPa, not Pa as the graph is in Pa x 10⁵
5
Q
Boyle’s Law - why might temp of gas have changed significantly during experiment
A
The temperature of a gas increases when compressed.
6
Q
Boyle’s Law - how did student ensure temp of gas was same for each measurement?
A
Wait a few mins before making readings after changing volume/pressure to allow the temp to stabilise
7
Q
Boyle’s Law - which is pressure and which is volume
A
- pressure is usually the bigger number, eg. 324 kPa
- V is usually the smaller number like 80 cm³
8
Q
Boyle’s Law - units used when measuring these quantities
A
kPa and cm³
9
Q
Boyle’s Law - method used to obtain the readings
A
- method of changing pressure/volume
- read pressure + volume
10
Q
Boyle’s Law - how pressure of gas varied during experiment
A
- connect air pump to oil reservoir of Boyle’s Law apparatus
- Pump air in until pressure gauge shows its at max.
- Close + remove tap
- Leave apparatus for a few mins to allow temp to stabilise
- Read pressure off Bourdon gauge
- Measure volume of liquid using scale on apparatus
- Open tap to release some air, then close. Leave for a few mins, then record pressure + volume again
- repeat a no. of times until pressure goes back to atmospheric pressure
11
Q
Boyle’s Law - how pressure + volume of gas was measured
A
- pressure read from the Bourdon gauge
- Volume measured from scale on on Boyle’s Law apparatus
12
Q
Boyle’s Law - why should there be a delay between adjusting pressure of gas and recording its value?
A
- allows for gas to cool and stabilise
- Allows liquid level to settle
13
Q
Boyle’s Law - sources of error
A
- ensure classroom temp remains constant
- be careful to take meniscus into account when reading the volume of liquid
14
Q
measure acceleration due to gravity “g” using free fall apparatus - method
A
- set up as per diagram
- switch electromagnet on so sphere stays in place
- attach timer to electromagnet + trapdoor, ensure it starts when it should
- measure distance s from bottom of ball to top of trapdoor
- set timer to zero, flick switch + record time taken for ball to reach trapdoor
- repeat three times, smallest value will be used in calculations
15
Q
measure acceleration due to gravity “g” using free fall apparatus - indicate distance s on your diagram
A
-distance indicated between bottom of ball + top of pressure plate/trapdoor
16
Q
measure acceleration due to gravity “g” using free fall apparatus - describe how time interval t was measured
A
- timer starts when ball leaves release mechanism
- timer stops when ball hits trap door
- measured using timer attached to electromagnet and trapdoor
17
Q
measure acceleration due to gravity “g” using free fall apparatus - graph
A
x-axis: time² (s²)
y-axis: distance s (m)
18
Q
measure acceleration due to gravity “g” using free fall apparatus - finding g using slope
A
g = 2 x slope
19
Q
measure acceleration due to gravity “g” using free fall apparatus - ways of minimising effect of air resistance on experiment
A
- small, smooth sphere
- no draughts
- in vacuum
- heavy/dense sphere
- distances relatively short
20
Q
measure acceleration due to gravity “g” using free fall apparatus - finding g using equation
A
use s = ut + 1/2at², a will be g
21
Q
measure acceleration due to gravity “g” using free fall apparatus - sources of error
A
- use a heavy, dense, small, smooth ball
- make sure no draughts in room
- measure from bottom of ball to top of trapdoor
- make falling distance relatively short
- repeat each run three times
- use a centi or milli-second timer
22
Q
measure acceleration due to gravity “g” using free fall apparatus - why use a small iron sphere
A
- reduce air resistance
- allows sphere to be held by electromagnet
23
Q
measure acceleration due to gravity “g” using free fall apparatus - assumptions made when calculating a value for acceleration due to gravity
A
- sphere starts moving immediately when timer is started (no time delay)
- air resistance is negligible
- gravity is the only force acting on it
24
Q
relationship between period and length of a pendulum + calc acceleration due to gravity, g - method
A
- clamp one end of string between flat faces of split cork. Tie bob to other end of string
- hang bob over edge of bench. Ensure free to move, no draughts, movement around room kept to min
- measure distance from bottom of cork to centre of bob (length l of pendulum)
- start with longest possible length for l
- set swinging at angle no greater than 5° (check with protractor)
- measure time taken for 30 oscillations, 30T. Divide by 30 to find time taken for one swing
- repeat three times
- decrease length of pendulum + repeat for diff lengths
25
relationship between period and length of a pendulum + calc acceleration due to gravity, g - why use a small angle
formula is only valid only for a small angle / SHM only occurs for a small angle
26
relationship between period and length of a pendulum + calc acceleration due to gravity, g - how to suspend the pendulum from a fixed point
use split cork/two coins
27
relationship between period and length of a pendulum + calc acceleration due to gravity, g - between which points was the length of pendulum measured?
-bottom of cork/coins to middle of bob
28
relationship between period and length of a pendulum + calc acceleration due to gravity, g - which t value is most accurate?
the biggest t value, smallest percentage error
29
relationship between period and length of a pendulum + calc acceleration due to gravity, g - graph
x-axis: Period²/T² (s²)
| y-axis: l (m)
30
relationship between period and length of a pendulum + calc acceleration due to gravity, g - using graph to find g
g = 4π² x slope of line
31
relationship between period and length of a pendulum + calc acceleration due to gravity, g - sources of error
- time taken for large no. of swings taken so average length for a swing can be calculated. This reduces error
- In-extensible string used to ensure it does not stretch as it swings, would distort result
- string clamped tightly to ensure length not affected
- heavy bob used to keep string taut + reduce air friction
- small angle of swing used to ensure pendulum moves w/ SHM
- no draughts, affect bob as it swings
32
relationship between period and length of a pendulum + calc acceleration due to gravity, g - how to obtain value for length of pendulum + its corresponding periodic time
-measure length l from bottom of cork to centre of bob using metre stick
or
-measure length l from bottom of cork to top of bob
-measure diameter of bob using vernier calipers
-length
-length = l + radius
-measure time taken for n oscillations, then divide total time by n
33
relationship between period and length of a pendulum + calc acceleration due to gravity, g - two factors that affect accuracy of measurement of periodic time
- number of oscillations selected
- precision of timer
- smaller percentage error in T with longer lengths
- nature of string eg in-extensible string
34
relationship between period and length of a pendulum + calc acceleration due to gravity, g - why measure time for 30 oscillations
reduce percentage error in the period, get average time (taken for one oscillation)
35
relationship between period and length of a pendulum + calc acceleration due to gravity, g - how to ensure length remained constant as it swung
- in-extensible string
| - string suspended at a fixed point (eg. split cork)
36
relationship between period and length of a pendulum + calc acceleration due to gravity, g - relationship
T²∝ l
37
relationship between period and length of a pendulum + calc acceleration due to gravity, g - why small heavy bob used
-to reduce air resistance + keep string taut
38
relationship between period and length of a pendulum + calc acceleration due to gravity, g - why string inextensible
-so length remains constant
39
relationship between period and length of a pendulum + calc acceleration due to gravity, g -describe how pendulum was set up
-string placed between split cork
40
relationship between period and length of a pendulum + calc acceleration due to gravity, g -precautions when allowing pendulum to swing
- small angle
- no draughts
- one plane only
- avoid spinning
41
relationship between period and length of a pendulum + calc acceleration due to gravity, g - how graph verifies relationship
straight line through origin verifies T²∝ l
42
constant velocity of an object - method
- set up as per diagram
- place track on bench, adjust levelling screws to ensure no slope on track
- turn on blower, adjust screws so trolley not moving due to air blowing
- turn off blower
- measure width of card (the distance) using metre stick + attach to trolley at height that will block beam of light gates
- turn on blower, give trolley push
- record time taken for card to block + unblock beam at each light gate. Displayed on data logger
- calculate velocity using distance and time values
43
constant velocity of an object - graph
distance-time graph
44
constant velocity of an object - finding velocity using graph
slope is velocity
45
constant velocity of an object - velocity formula
v = d/t
46
constant velocity of an object - sources of error
- make sure track is level when blower is on, or trolley may accelerate
- use two light gates in order to find velocity at two points. Ensures velocity remains constant
- adjust amount of air coming out of blower, make sure trolley remains in position when untouched
- adjust height of card so it blocks + unblocks light gate
47
measure constant acceleration of an object - method
- set up as per diagram
- place track on bench, adjust + ensure no slope on track
- attach + turn on blower, adjust screws so trolley no moving due to air blowing
- turn off blower
- measure distance s, using metre stick, between light gates
- measure width of card, d, + attah to trolley at heigh that will block beam of light gates
- Place weight on pan + hold pan until experiment ready
- turn on blower, give trolley push + check it accelerates as it travels
- record time taken for card to block + unblock beam at each light gate + therefore find velocity at start + end of journey
- repeat with diff weights
48
measure constant acceleration of an object - graph
velocity-time graph
49
measure constant acceleration of an object - sources of error
- ensure track is level when blower is on
- adjust amount of air coming out of blower so trolley remains in position when untouched
- adjust height of card so it blocks + unblocks light gate
50
measure constant acceleration of an object - steps in measuring acceleration of the body
- measure width of card on trolley using metre stick
- -record time taken for card to block + unblock beam at each light gate
- therefore find initial and final velocities
- record time interval from initial to final velocities and use v=u+at
51
measure constant acceleration of an object - what graph tells you about relationship
straight line thru origin??
a ∝ F
52
measure constant acceleration of an object - use graph to find mass of body
- slope
| - f = ma?
53
measure constant acceleration of an object - suggest why the graph might not go through the origin + how apparatus should be adjusted so it does
- friction
| - adjust track, use blower
54
equilibrium - method
- find centre of gravity of metre stick by hanging from single loop of string + adjusting until balanced
- Find weight of metre stick by hanging it from a Newton spring balance
- Set up as per diagram
- Place weights at various positions, ensuring it is balanced each time
- Measure distance (using the scale on metre stick) of each force from a chosen point on metre stick
- Calculate the upwards and downwards forces and calculate the moments
- change the position of the balances and repeat for diff weight and distance values a number of times
55
equilibrium - sources of error
- centre of gravity may not be at centre due to chips that have come off metre stick or due to scale not starting exactly at zero on exact end of stick
- make sure metre stick is horizontal before taking any distance readings. If at an angle, sine and cosine of angle of incline will have to be factored into calculations
56
equilibrium - how centre of gravity was found
- balance horizontally on a pivot/at a point
| - suspend horizontally from a thread/string
57
equilibrium - how weight of metre stick was found
-newton balance
or
-mass balance and multiply by g
58
equilibrium - how upward forces and downward forces were determined
- upward: newton balances
| - downward: known weights
59
equilibrium - why centre of gravity is not at 50.0 cm mark
- metre stick not uniform
- stick chipped
- extra material on one end
- stick worn at one side
- stick could've had a hole in one side
60
equilibrium - explain how your calculations verify the laws of equilibrium
net vertical force ≈ 0 N
sum of moments about a point ≈ 0 Nm
or
forces up = forces down
total clockwise moments ≈ total anticlockwise moments
61
equilibrium - how to ensure system was at equilibrium
how to ensure metre stick was in equilibrium
system not moving
metre stick was at rest/balanced
62
verify principle of conservation of momentum - method
- set up as per diagram
- measure width (distance) of card using metre stick, attach to trolleys at height that will block beam of light gates
- adjust levelling screws to ensure no slope on track
- attach + turn on blower, place trolleys over track, adjust screws until trolleys not moving due to air blowing underneath it
- give trolley 1 a push, record time taken for card to block and unblock beam at first light gate (on data logger)
- Record time taken for two trolleys to block + unblock the second light gate
- Use distance and time values to calculate initial velocity of trolley 1 and the final velocity of the two trolleys
- find mass of each trolley on electronic balance
- place weights on trolleys and repeat a number of times for diff values of mass
63
verify principle of conservation of momentum - sources of error
- friction and gravity have been minimised by using air track and horizontal track
- magnets or blutac used to attach two trolleys to ensure system of bodies in collision act as one
64
verify principle of conservation of momentum - state what measurements the student took and how these measurements were used to calculate the velocities
- masses of trolleys
- time for card to block and unblock beam at first light gate and time taken for two tolleys to block and unblock second light gate
- length of card
calculate: velocity = distance/time
65
verify principle of conservation of momentum - using the recorded data, show how the experiment verifies the principle of conservation of momentum
find mu
find mv + mv
(or use conservation of momentum formula)
they should be approx the same, but don't worry if they're not exactly the same.
eg: 0.273 kg m/s ≈ 0.277 kg m/s
66
verify principle of conservation of momentum - forces that need to be taken into account to ensure no net external forces are acting on bodies + how to reduce effects of these forces
- Weight (Gravitational force)
- Friction
minimised by: using a horizontal air track
- air cushion to separate surfaces
- horizontal track
67
verify principle of conservation of momentum - adjustments to make sure body A would move at constant velocity
- adjust gradient of track
| - clear holes of air track
68
verify principle of conservation of momentum - how student knew body A was moving at constant velocity
- same time interval shown by both light gates
| - horizontal line on v vs t graph (datalogging method)
69
verify principle of conservation of momentum - describe how to measure velocity v of bodies after collision
- measure length of card using metre stick (this is the distance)
- Record time taken for two trolleys to block + unblock the second light gate (on data logger)
- velocity = distance/time
70
verify principle of conservation of momentum - how could accuracy of experiment be improved?
select greater distance
avoid parallax error
use digital balance
71
verify principle of conservation of momentum -describe how the time was measured
- two light gates and card on trolley
| - read times on data logger
72
verify principle of conservation of momentum - show how experiment verifies the principle of conservation of momentum
use calculations
momentum before ≈ momentum after
73
acceleration proportional to force - method
- set up as like the other trolley experiments
- place all but one of the weights on trolley, place last weight on pan
- record mass of this weight in pan
- hold pan until ready
- position trolley at other end of track
- give trolley push, record time taken for card to block + unblock beam at each light fate
- find velocity at start and end of journey, then use to calculate acceleration of trolley
- transfer a weight from trolley to pan, repeat process, record new mass on pan
- repeat until all weights transferred to pan
74
acceleration proportional to force - graph
x-axis: F (N)
| y-axis: a (m/s2)
75
acceleration proportional to force - conclusion from graph
straight line thru origin verifies a directly proportional to F
-as force applied to pan increased, acceleration of trolley increased
76
acceleration proportional to force - error
- track level
- adjust air
- adjust height of card
77
equilibrium calculations
-dont forget to draw in the force of the weight of the ruler acting in the centre
-Write net forces/sum of moments as
net force ≈ x , sum of moments ≈ y
