RP: Determination of G

• What is the overall aim of the experiment?

  To calculate the value of acceleration due to gravity, g
• How is the acceleration due to gravity calculated in this experiment?

  By measuring the time for a ball-bearing to fall

  
• What is the independent variable in the experiment?

  Height, h
• What is the dependent variable in the experiment?

  Time, t
• What are the control variables in the experiment?

  • Same steel ball-bearing
  • Same electromagnet
  • Distance between ball-bearing and top of the glass tube
• What is the resolution of the metre ruler used in the experiment?

  1 mm
• What is the resolution of the timer used in the experiment?

  0.01 s
• What is the method for measuring the time taken for the ball-bearing to drop?

  1. Set up apparatus with electromagnet and glass tube.
  2. Measure distance between light gates as height, h.
  3. Switch on electromagnet and drop ball-bearing.
  4. Record time when ball passes through light gates.
  5. Repeat for different heights and calculate average time.
• How should the glass tube be positioned?

  Directly downwards, not at an angle
• What happens when the ball-bearing drops through the first light gate?

  The timer starts

  
• What happens when the ball-bearing drops through the second light gate?

  The timer stops
• How many values for height should be used in the experiment?

  At least 5 – 10 values
• What is the process for calculating acceleration in this experiment?

  1. Use SUVAT equations.
  2. Known quantities:

  • Displacement s = h
  • Time taken = t
  • Initial velocity u = 0
  • Acceleration a = g

  1. Rearrange the equation to find g.
• What is the equation used to find the acceleration due to gravity?

  Rearranged SUVAT equation
• What does the gradient of the graph represent in this experiment?

  The acceleration due to gravity, g
• How is the error in g calculated?

  By comparing best and worst fit lines
• What are the types of errors identified in the experiment?

  • Systematic Errors:
  • Residue magnetism affecting time recording
  • Random Errors:
  • Uncertainty in height measurement
  • Parallax error in reading height
  • Ball not falling accurately through light gates
• How can random errors be reduced in this experiment?

  By repeating the experiment multiple times
• What safety considerations should be taken into account?

  • Avoid water near the electromagnet.
  • Switch on current only after setup.
  • Use a cushion to catch the ball-bearing.
  • Secure the clamp stand with a G clamp.
• What are the steps to calculate g from the table?

  1. Complete the table with average times.
  2. Add a column for $2h/t$.
  3. Draw graph of $2h/t$ against time $t$.
  4. Calculate the gradient of the graph.