Paper 3: Required practical 3 - Determination of g

Question 1

What graph can be plotted from experimental data to determine g?

Answer 1

A graph of 2h/t against t can be plotted
The value of g is the gradient

Question 2

How can an electromagnetic be used to determine g?

Answer 2

• A magnetic ball bearing can be released by an electromagnet clamped at a known height
• The timing system starts when the electromagnet is switched off, and the timer is stopped when the ball lands on the finish pad

Question 3

What safety precaution should be taken when using an electromagnet?

Answer 3

• Electromagnets heat up over time
• To reduce the heating effect, you should switch it off when not in use

Question 4

How can light gates be positioned so the the ball falls directly through them?

Answer 4

A plumb line could be used to demonstrate the expected path of the ball

Question 5

Why is it an advantage to use a small ball-bearing over a larger ball?

Answer 5

• The smaller the ball, the smaller the effects of air resistance
• With a small ball these effects can be considered negligible

Question 6

Why should there be a gap between the release poistion and the first light gate?

Answer 6

To ensure that the time over which the ball is passing through the light gate is negligible (moving sufficiently quick enough)

Question 7

Why would the experiment not be valid if the air resistance acting on the ball wasn’t negligible?

Answer 7

• The ball wouldn’t be in free fall since acceleration wouldn’t be purely due to the force of gravity
• The acceleration would also be variable since air resistance increases with speed so the uniform acceleration equations couldn’t be used

Question 8

Why sould the value of g not be the same as the accepted value?

Answer 8

• Delays in timing equipment (if using a stop clock this will be human reaction time)
• Resisitive forces may be significant
• Errors in height measurements such as measuring from different positions on the ball each time

Question 9

How could your results be improved?

Answer 9

• Take repeat readings at each height and then calculate the mean time
• Ensure the height measurements are taken from the same position on the ball each time

Question 10

What is the advantage of using light gates over a stop clock?

Answer 10

• Light gates should result in a lower uncertainty in your time measurements
• A stop-clock will involve human reaction times and therefore an associated error