# finding acceleration of free fall using electromagnet! How do i find initital speed

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#1
how do I find u because the ball bearing moves some distance before it passes through the first light gate (which starts the timer) Please help? Thanks.
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3 years ago
#2
(Original post by sarah99630)
how do I find u because the ball bearing moves some distance before it passes through the first light gate (which starts the timer) Please help? Thanks.
You'll have to give more details of the particular experiment before anyone can say for sure. The versions I've seen either start the timer when the ball is released by the electromagnet (so u = 0), or the experiment is done repeated times for different s so that u can be eliminated (it should always be the same).
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#3
(Original post by Pangol)
You'll have to give more details of the particular experiment before anyone can say for sure. The versions I've seen either start the timer when the ball is released by the electromagnet (so u = 0), or the experiment is done repeated times for different s so that u can be eliminates (it should always be the same).
hmm I think I'll use the procedure of u being zero..it's so much more simpler... I'll look it up on youtube to clarify how the graph will look like if I used the gradient to find the acceleration and one of the suvat equations,thank you!
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3 years ago
#4
(Original post by sarah99630)
how do I find u because the ball bearing moves some distance before it passes through the first light gate (which starts the timer) Please help? Thanks.
The following video may help to clarify something

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#5
(Original post by Eimmanuel)
The following video may help to clarify something

that's the video I watched and I Understood everything except that u bit. If I use the same method except I leave no distance between the first light gate and the ball bearing at rest,will it work? Although idk what will happen to the y axis of the graph now...that is if I can still use the same equation and arrangement. Oh and thanks a lot.

that's the video I watched and I Understood everything except that u bit. If I use the same method except I leave no distance between the first light gate and the ball bearing at rest,will it work? Although idk what will happen to the y axis of the graph now...that is if I can still use the same equation and arrangement. Oh and thanks a lot.
0
3 years ago
#6
(Original post by sarah99630)
... If I use the same method except I leave no distance between the first light gate and the ball bearing at rest,will it work? Although idk what will happen to the y axis of the graph now...that is if I can still use the same equation and arrangement. Oh and thanks a lot.
Yes it would work...but (see below)

(Original post by sarah99630)
... Although idk what will happen to the y axis of the graph now...that is if I can still use the same equation and arrangement. Oh and thanks a lot.
If u is really zero, you just need to plot s versus t2 or 2s versus t2.
And use the gradient to find the acceleration due to gravity.

--------------
Below is for the but...

If you are going to leave no distance between ball bearing and the first light gate, (by theory) the initial speed is zero. This is just an assumption. As you should know almost all set-up would introduce some sort of uncertainty or error, how can you be sure that the set-up really introduces zero initial speed. We assume that the iron ball "loses all its magnetism" and falls from rest. If you have done the experiment and use your hand to touch electromagnet, you can feel that there is a slight vibration (Wear a rubber glove before touching the electromagnet for safety reason. For most electromagnet in the school lab, it is quite safe to touch without wearing a rubber glove. If not, I would not be around anymore ). This slight vibration can introduce some errors to your experiment.

Hope it helps.

Forget to mention what is the vibration: at the instant when the electromagnet is turned off, there can be a slight vibration.
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#7
(Original post by Eimmanuel)
Yes it would work...but (see below)

If u is really zero, you just need to plot s versus t2 or 2s versus t2.
And use the gradient to find the acceleration due to gravity.

--------------
Below is for the but...

If you are going to leave no distance between ball bearing and the first light gate, (by theory) the initial speed is zero. This is just an assumption. As you should know almost all set-up would introduce some sort of uncertainty or error, how can you be sure that the set-up really introduces zero initial speed. We assume that the iron ball "loses all its magnetism" and falls from rest. If you have done the experiment and use your hand to touch electromagnet, you can feel that there is a slight vibration (Wear a rubbber glove before touching the electromagnet for safety reason. For most electromagnet in the school lab, it is quite safe to touch without waering a rubber glove. If not, I would not be around anymore ). This slight vibration can introduce some errors to your experiment.

Hope it helps.
ahaa now I get this experiment perfectly,much much appreciated.Thank you!
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