Module 3 Practicals Flashcards

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1
Q

Determine g
- Method (5)
- Graphs and Calculations (2)
- Safety (2)
- Validity (6)

A
  • Attach two light gates to a clamp stand
  • Measure the distance between the light gates (h) with a metre ruler
  • Switch on an electromagnet and attach a ball bearing
  • Switch off electromagnet and measure time taken (t) for the ball bearing to pass through the light gates using a data logger connected to the light gates
  • Change the distance between the light gates and repeat
  • Plot a graph of 2h against t2
    • s=ut+½ at2 → 2h = gt2 (y = mx)
  • g = the gradient of the graph
  • Place a pad beneath the light gates to avoid the ball bearing bouncing upwards and causing injury
  • Place a counterweight on the clamp stand to avoid it tipping over
  • Place the light gates as close as possible to the electromagnet
  • If the distance of fall is too large or the ball is too small, air resistance may have a noticeable effect
  • Keep the distance between the electromagnet and the upper light gate the same each time
    • So the ball bearing reaches the upper light gate with the same speed each time
  • Repeat the experiment 3 times for each height and find a mean
  • Using light gates and data loggers are more accurate than using a stopwatch due to reaction times
  • Adjust the current of the electromagnet so that it only just supports the ball bearing as to high a current would result in a delay in release
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2
Q

Determine the Terminal Velocity of a Falling Object
- Method (2)
- Graphs and Calculations (1)

A
  • Use light gates connected to a data logger
  • Time when each of the two light beams are broken by the object is recorded
  • Velocity = distance between two light gates/time taken
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3
Q

Determine the Terminal Velocity of an Object in a Liquid
- Method (3)
- Graphs and Calculations (3)
- Safety (1)
- Validity (3)

A
  • Wrap elastic bands around tube of viscous liquid at set intervals measured by ruler
  • Drop ball into tub and record the time it reaches each band using a stopclock
  • Use a strong magnet to remove the ball bearing from the bottom of the tube
  • Calculate time taken to travel between consecutive bands
    • calculate average time for each experiment
  • Calculate mean velocity = distance/mean time of the bearing between each set of bands
  • Plot a graph of velocity against cumulative time
    • The velocity which the graph tends to is the terminal velocity
  • Use a viscous liquid that doesn’t cause skin irritation
  • Repeat 4 times to reduce effect of random errors
  • Use a teller tube to allow bearing to travel at terminal velocity for longer
  • Using larger intervals between band reduced percentage uncertainty in both distance and time between bands
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4
Q

Finding the Stopping Distances for a Range of Starting Velocities
- Method (6)
- Graphs and Calculations (2)
- Validity (2)

A
  • Put an interrupter card on top of block of wood and measure its length using a metre ruler
  • Set up a light gate so that it records the average starting velocity of the block moving through it (around 2cm away from start position)
  • Record the block starting position
  • Push the block of wood through the light gate
  • Measure the distance from the light gate to where the wood stopped
  • Return block to its starting position and push it again with a different velocity
  • Initial velocity = length of interrupter card/time on data logger
  • Plot a graph of sopping distance against starting velocity2
    • Should be straight line through the origin as:
    • Ek of block = ½ mv2 = force x stopping distance (as all EK converted to thermal energy by friction)
  • Interrupter card allows the distance moved through the light gate to be fixed
  • Surface block is pushed on and block material should stay constant to frictional force varies as little as possible
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5
Q

Finding the Centre of Mass/Gravity of an Object
- Method (5)

A
  • Make three holes in random places around the edge of the object
  • Freely suspend the object from a clamp stand at once of the holes
    • Let it swing and come to rest
  • Use a plumb line to draw a vertical line downward on object from point of suspension to bottom of object
  • Repeat from different points of the object
  • The centre of mass will be the point where all the lines drawn intersect
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6
Q

Determine the Young’s Modulus of a Metal
- Method (6)
- Graphs and Calculations (6)
- Safety (3)
- Validity (2)

A
  • Measure diameter of wire (repeat x3) with a micrometer
  • Clamp wire horizontally across a table with masses hanging off it via a pulley
  • Attach a metre ruler to the table and place a marker on the wire where 0cm is
  • Measure the original length of the wire from the clamp stand to the marker
  • Attach a mass to the end and record total mass and new position of marker
  • Repeat this six times
  • Calculate the mean diameter of the wire and so find the average cross sectional area of the wire
  • Calculate the force exerted on the wire each time using F = mass x g
  • Calculate the extension of the wire each time using extension = new position of marker - original length
  • Calculate the stress (F/A) and strain (x/L) for each reading
  • Plot a stress-strain graph and draw a line of best fit
  • The gradient of the line of bets fit is Young’s modulus
  • Wear eye protection as wire could snap and fly off
  • Place some cushioning beneath the masses so they will not bounce back up if the wire snaps and releases them
  • Place horse shoe shaped protectors over wire to prevent flying off if it snaps
  • Make original length of the wire as long as possible to reduce the uncertainty
  • Make sure wire is relatively thin as thinner the wire, greater the extension
    • A larger extension will reduce the uncertainty
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7
Q

Investigating a Property of Plastic
- Method (7)
- Graphs and Calculations (3)
- Safety (1)
- Validity (1)

A
  • Use a guillotine to slice a plastic bag lengthways and widthways
  • Hole punch one end of the plastic strip
  • Attach plastic strip to a clamp stand and measure its original length while taut with a ruler
  • Attach a 100g mass to the plastic from hole punch and measure new length
  • Repeat with more masses
  • Apply this method to other strips that are widthways/lengthways
  • Repeat the experiment recording the new length after removing masses to get data for unloading as well as loading
  • Calculate extension using: extension = new length - original length
  • Calculate the force applied using: Force = mass x g
  • Plot a graph of force against extension for loading and unloading
  • Cushion the floor below so masses do not bounce back up if they fall
  • Using a hole punch means the force isn’t evenly distributed through the strip but is concentrated near the hole
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8
Q

Investigating Springs in Series and Parallel
- Method (3)
- Graphs and Calculations (4)
- Safety (2)
- Validity (2)

A
  • Attach 2 springs in series/parallel and measure original length using a ruler
  • Attach the mass and measure the new length of the springs
  • Add more springs and repeat
  • Calculate extension for each combination using: new length - original length
  • Find the spring constant for each combination using: k = Force applied (mass x g) / extension of combination
  • Series:
    • In theory: 1/kcombination = 1/k1 + 1/k2 + …
      • Since xcombined = x1 + x2
      • F=kx so F/kcombined = F/k1 + F/k2 and divide by F
  • Parallel:
    • In theory: kcombination = k1 + k2 + …
      • Since Fcombined = F1 + F2
      • F=kx so xkcombined = xk1 + xk2 and divide by x
  • Do not extern too high a force on the springs so the springs don’t break
  • Wear eye protection
  • Using too high a force can permanently deform the springs
  • Always measure from the same point - use a marker
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