PAG 1.1 Comparing Methods Of Determining g Flashcards
What is meant by free-fall?
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 are considered negligible)
What is g?
Gravitational Field Strength (on the surface of the Earth)
Why can SUVAT equations by used in this experiment?
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 t^2 against h, how is g determined?
The gradient is t^2/h
Consequently the acceleration (g) will be equal to 2/gradient
Comes from the equation s=ut+1/2at^2
(s=1/2at^2 as u=0)
When plotting a graph of v^2 against h, how is g determined?
Gradient is v^2/h
Acceleration (g) is half the gradient
Comes from the equation v^2=u^2-2as
Describe how an electromagnet system can be used to determine 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 precautions should be taken?
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?
Electromagnets heat up over time. To reduce this heating effect, 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
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?
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?
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
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 the 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
Delays in timing equipment (stopwatch=human reaction time)
Resistive forces are acting
Errors in height measurements, such as measuring different positions on the ball each time
What is the advantage of using light-gates over a stop clock in this experiment?
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?
Take repeat reading at each height and then calculate the mean time taken
Ensure height measurements are taken from the same position each time
