Mechanics experiments Flashcards
Boyle’s Law - method
- 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
Boyle’s Law - graph
x-axis: 1/V (1/cm³)
y-axis: Pressure (Pa x 10⁵)
Boyle’s Law - how graph verifies Boyle’s law
straight line through origin verifies p ∝ 1/V
Boyle’s Law - use graph to estimate pressure of gas at volume of ___
- 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
Boyle’s Law - why might temp of gas have changed significantly during experiment
The temperature of a gas increases when compressed.
Boyle’s Law - how did student ensure temp of gas was same for each measurement?
Wait a few mins before making readings after changing volume/pressure to allow the temp to stabilise
Boyle’s Law - which is pressure and which is volume
- pressure is usually the bigger number, eg. 324 kPa
- V is usually the smaller number like 80 cm³
Boyle’s Law - units used when measuring these quantities
kPa and cm³
Boyle’s Law - method used to obtain the readings
- method of changing pressure/volume
- read pressure + volume
Boyle’s Law - how pressure of gas varied during experiment
- 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
Boyle’s Law - how pressure + volume of gas was measured
- pressure read from the Bourdon gauge
- Volume measured from scale on on Boyle’s Law apparatus
Boyle’s Law - why should there be a delay between adjusting pressure of gas and recording its value?
- allows for gas to cool and stabilise
- Allows liquid level to settle
Boyle’s Law - sources of error
- ensure classroom temp remains constant
- be careful to take meniscus into account when reading the volume of liquid
measure acceleration due to gravity “g” using free fall apparatus - method
- 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
measure acceleration due to gravity “g” using free fall apparatus - indicate distance s on your diagram
-distance indicated between bottom of ball + top of pressure plate/trapdoor
measure acceleration due to gravity “g” using free fall apparatus - describe how time interval t was measured
- timer starts when ball leaves release mechanism
- timer stops when ball hits trap door
- measured using timer attached to electromagnet and trapdoor
measure acceleration due to gravity “g” using free fall apparatus - graph
x-axis: time² (s²)
y-axis: distance s (m)
measure acceleration due to gravity “g” using free fall apparatus - finding g using slope
g = 2 x slope
measure acceleration due to gravity “g” using free fall apparatus - ways of minimising effect of air resistance on experiment
- small, smooth sphere
- no draughts
- in vacuum
- heavy/dense sphere
- distances relatively short
measure acceleration due to gravity “g” using free fall apparatus - finding g using equation
use s = ut + 1/2at², a will be g
measure acceleration due to gravity “g” using free fall apparatus - sources of error
- 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
measure acceleration due to gravity “g” using free fall apparatus - why use a small iron sphere
- reduce air resistance
- allows sphere to be held by electromagnet
measure acceleration due to gravity “g” using free fall apparatus - assumptions made when calculating a value for acceleration due to gravity
- sphere starts moving immediately when timer is started (no time delay)
- air resistance is negligible
- gravity is the only force acting on it
relationship between period and length of a pendulum + calc acceleration due to gravity, g - method
- 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
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
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
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
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
relationship between period and length of a pendulum + calc acceleration due to gravity, g - graph
x-axis: Period²/T² (s²)
y-axis: l (m)
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