PAG 01.1 - Comparing Methods of Determining g Flashcards
What is meant by free-fall?
Determining g
Determining g
PAG 01.1 - Comparing Methods of Determining g
An object is said to be falling in free-fall if the only force acting on it is gravity. This means that no resistive forces are acting (or in practice they are considered
negligible).
What is ‘g’?
Determining g
PAG 01.1 - Comparing Methods of Determining g
Gravitational Field Strength (in our case, on the surface of Earth)
Why can the SUVAT equations be used in this experiment?
PAG 01.1 - Comparing Methods of Determining g
The SUVAT equations can be used since the object will fall with uniform acceleration. This is because the force of gravity is constant at the Earth’s surface.
When plotting a graph of t² against h, how is ‘g’ determined?
PAG 01.1 - Comparing Methods of Determining g
The gradient of the graph will be t²/h. Consequently, the acceleration (‘g’) will be equal to 2/gradient. This comes from the equation s = ut + ½ at², where s=h, a=g and u=0.
When plotting a graph of v² against h, how is ‘g’ determined?
PAG 01.1 - Comparing Methods of Determining g
The gradient of the graph will be v²/h. Consequently, the acceleration (‘g’) will be equal to half the gradient. This comes from the equation v² = u² - 2as, where s=h, a=g and u=0.
Describe how an electromagnet system can be used to determine ‘g’.
PAG 01.1 - Comparing Methods of Determining g
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.
When using a clamp stand in this experiment, what safety precaution should be taken?
PAG 01.1 - Comparing Methods of Determining g
The clamp stand should have a counterweight or G-clamp attached to its base to provide a moment to prevent it toppling over.
What safety precaution should be taken when using an electromagnet?
PAG 01.1 - Comparing Methods of Determining g
Electromagnets heat up over time. To reduce this heating effect, you should switch it off when not in use.
Suggest how light-gates could be positioned to ensure that the ball or dowel falls directly through them.
PAG 01.1 - Comparing Methods of Determining g
A plumb line could be used to demonstrate the expected path of the object. This allows the light-gates to be positioned in appropriate places so that the ball will fall through them.
Why is it advantageous to use a small ball-bearing over a larger ball?
PAG 01.1 - Comparing Methods of Determining g
The smaller the ball, the smaller the effects of air resistance. In the case of a small ball-bearing these effects can be considered negligible.
Why should there be a gap between the release position and the first light-gate?
PAG 01.1 - Comparing Methods of Determining g
There should be a gap to ensure that the time over which the ball is passing through the light gate is negligible (the ball is moving sufficiently quick enough).
Explain why this experiment would not be valid if the air resistance acting on the ball wasn’t negligible.
PAG 01.1 - Comparing Methods of Determining g
The ball wouldn’t be in free-fall since the acceleration would not be purely due to the force of gravity. The acceleration would also be variable since air resistance increases with speed, and so the uniform acceleration equations couldn’t be used.
Suggest why your obtained value of ‘g’ may not be the same as the accepted value.
PAG 01.1 - Comparing Methods of Determining g
- Delays in the timing equipment (if using a stop clock, this will be human reaction time)
- Resistive forces are acting
- Errors in height measurements, such as measuring from different positions on the ball each time
What is the advantage of using light-gates over a stop-clock in this experiment?
PAG 01.1 - Comparing Methods of Determining g
Using light-gates should result in a lower uncertainty in your time measurements. A stop-clock will involve human reaction times.
How could your results be improved?
PAG 01.1 - Comparing Methods of Determining g
You should take repeat readings at each height and then calculate the mean time taken. You should also ensure that height measurements are taken from the same position each time.