Halp! (2 Viewers)

[ohexploitable]

Just a few questions...

In the pendulum experiment to find 'g', what are some controlled variables? I was thinking the person timing it and string material but they seem kinda shit.

And what are the controlled variables in the experiment to observe the motor effect while changing the current direction and magnetic field direction? Like you have a battery connected to some aluminium foil using connecting wires and the foil is placed in a magnetic field and you observe what happens when you reverse the current and reverse the magnets.

 

[khorne]

lol OE, how ironic, do you not think?

1) more important to know independant/dependant variables than controlled. Controlled variables could be size of masses (although mass doesn't influence it, air resistance does), types of string used is important one too. The thing is, it's not an experiment in the true sense, it's merely collecting data for a mathematical model. The model has been proven, so they only need values etc.

 

[ohexploitable]

lol OE, how ironic, do you not think?

How so?

 

[hscishard]

idk say same equipment and some other things that are left unchanged

 

[Fizzy_Cyst]

Just a few questions...

In the pendulum experiment to find 'g', what are some controlled variables? I was thinking the person timing it and string material but they seem kinda shit.

And what are the controlled variables in the experiment to observe the motor effect while changing the current direction and magnetic field direction? Like you have a battery connected to some aluminium foil using connecting wires and the foil is placed in a magnetic field and you observe what happens when you reverse the current and reverse the magnets.

The angle to the vertical at which you hold the mass. The mass itself. The string definately (different materials have different elasticities etc...)

For the second experiment

controlled variables could be size of current/voltage source, length of Al strip, strength of magnetic fields

Although, this really isn't a quantifiable experiment, these values do not really matter. It is more a "yes/no" answer rather than a quantitative answer.

A better example of a motor effect experiment is placing a copper wire on a sensitive balance. Passing current through it in the presence of a magnetic field and seeing how the reading on the balance changes. This actually gives you quantitative results and you are able to work out the actual strength of the magnetic field

 

[ohexploitable]

The angle to the vertical at which you hold the mass. The mass itself. The string definately (different materials have different elasticities etc...)

The period is independent of the mass and the angle of swing, they don't need to be controlled me thinks.

Although, this really isn't a quantifiable experiment, these values do not really matter. It is more a "yes/no" answer rather than a quantitative answer.

Exactly. I talked to my teacher and got this question removed from the assessment and it was poop.

 

[Fizzy_Cyst]

The period is independent of the mass and the angle of swing, they don't need to be controlled me thinks.

True, but the experiment itself is actually an approximation of simple harmonic motion. The approximation only holds true for small angles (less than about 10degrees from horizontal), and as long as the tension in the string can be maintained. i.e., if you have a 50g mass for one length and a paperclip for another length, tension will not be maintained for the mass of the paperclip and the results you will get will not be valid. Hence, you need to control both angle and mass of the 'bob'

 

[khorne]

point is... g isn't related to angle or mass so it doesn't matter, because you obviously have a 10+g mass hanging off, enough to tense a string.

 

[OmmU]

Just a few questions...

In the pendulum experiment to find 'g', what are some controlled variables? I was thinking the person timing it and string material but they seem kinda shit.

And what are the controlled variables in the experiment to observe the motor effect while changing the current direction and magnetic field direction? Like you have a battery connected to some aluminium foil using connecting wires and the foil is placed in a magnetic field and you observe what happens when you reverse the current and reverse the magnets.

1. Possibly environmental conditions such as wind etc. Also the altitude that the experiment is conducted at (^_^) lol as it has a minimal (but still an affect) on the acceleration due to gravity.

2. Strength of the magnet is kept constant. Amount of current kept constant. Also maybe; speed at which you bring the magnet it.

 

[elbatiolpxeho]

2. Strength of the magnet is kept constant. Amount of current kept constant. Also maybe; speed at which you bring the magnet it.

The experiment is designed to observe the direction a current carrying conductor will move in the presence of a magnetic field, the strength of the field and magnitude of the current has no effect on the direction, they only need to be high enough for an observable deflection.

 

[Fizzy_Cyst]

point is... g isn't related to angle or mass so it doesn't matter, because you obviously have a 10+g mass hanging off, enough to tense a string.

It is not 'g' which you are measuring.. You are measuring Period (T) and determining g from this. Period is affected by angle. as the equation which is used in most pendulum practicals is a small angle approximation i.e., the equation which you use only works for small angles meaning it needs to be at a small angle in order to satisfy the small angle approximation

If you need any further clarification, use google =) I am unsure how to use Latex to prove it to you. (Search for Mathieu's equation)

Your teacher should tell you that it is an approximation.

You are correct with the mass itself, as long as tension can be maintained, mass doesn't really matter.

But in order for an experiment to be 'fair' and 'valid' all variables are to be controlled except the independent. If you change the mass between different lengths, there is no way you can directly attribute your change in results solely to the length.

The whole purpose of an experiment is so you can say that y changes due to changes in x. If you change z as well, you cannot directly say that change in y is due to change in x, as z may have caused changes also.