Smooth pulley system - frictionless Atwood machine (A Level Maths / Physics)

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Dr Ben Yelverton

Dr Ben Yelverton

3 жыл бұрын

A classic dynamics problem involving two masses hanging from either side of a smooth pulley. How can we calculate their acceleration, and the tension in the string connecting them?
About me: I studied Physics at the University of Cambridge, then stayed on to get a PhD in Astronomy. During my PhD, I also spent four years teaching Physics undergraduates at the university.
My website: benyelverton.com
#physics #maths #mechanics #dynamics #forces #pulley #string #rope #alevel

Пікірлер: 7
@nnmm789
@nnmm789 2 жыл бұрын
So Useful THX FOR UR Effort
@GabrielConstantinides
@GabrielConstantinides Жыл бұрын
Thanks for the video Ben, I'd like to ask a question about the assumption for the pulley being smooth if you have the time to answer it. The tension in the string is the same on either side of the pulley due to it being smooth. Suppose that the pulley wasn't smooth, how would this affect the tension on each side on the string? All I can think of (and I am not sure if my thoughts are correct) is that the tension in the string on side with the greater mass increases in order to overcome the frictional force? I'd really appreciate an answer to this Ben, thanks in advance if you can provide it.
@DrBenYelverton
@DrBenYelverton Жыл бұрын
Thanks for watching! That's exactly right, the tension ends up higher on the side with the greater mass. Also, for a smooth pulley, there is only equilibrium if the mass ratio m₂/m₁ is exactly 1, but if it's not smooth then the system can remain in equilibrium when the mass ratio is within some range determined by the coefficient of friction. I actually have a video going into detail on this if you're interested: kzfaq.info/get/bejne/rtBhgc1nxLHWd58.html And for completeness, the derivation of an equation I use in that video: kzfaq.info/get/bejne/ipqnic-AvqzTeGw.html
@GabrielConstantinides
@GabrielConstantinides Жыл бұрын
@@DrBenYelverton thanks so much Ben for replying to me. I appreciate the thoughtfulness of your response, and how quickly you got back to me. I hope to watch the suggested videos if I make it further into my mechanics studies (understanding the concepts I find very challenging). The videos may answer my question, though incase not I want to ask for some extra detail here. Why does the side of the pulley with greater mass supply the extra tension, and not the side with the lower mass? What I said in my initial comment was just a guess really, and it seems I got lucky.
@DrBenYelverton
@DrBenYelverton Жыл бұрын
​@@GabrielConstantinides It's probably easiest to understand this by first considering the case where both masses are stationary. Then it follows (by considering the free body diagram of each particle) that the tension on each side is equal to the weight of the particle on that side, and hence the tension is larger on the side with a larger mass. If you then keep the lighter mass fixed but gradually increase the heavier mass, then the tension on the heavier side continues to increase, while the tension on the lighter side remains fixed. There's now a difference in tension between the two sides, which means the system wants to start accelerating, but friction can prevent this up to a certain point. Once the tension difference is large enough (the exact meaning of "large enough" depends on the coefficient of friction) then it will start accelerating, with the tension on the heavier side still being larger. I think this all sounds quite complicated but essentially it just comes down to the fact that the heavier mass is pulling harder, so produces more tension in the rope!
@GabrielConstantinides
@GabrielConstantinides Жыл бұрын
@@DrBenYelverton thanks so much Ben, the last part you said about the heavier mass pulling harder is a really good way to summarise it. I hope I will manage to make more sense of all this stuff if I put the work in. Do you have a tip jar or anything so I can pay tribute? It won't be much, but I'd like to show my appreciation
@DrBenYelverton
@DrBenYelverton Жыл бұрын
@@GabrielConstantinides No problem - it takes time to build up intuition about these things. Thanks for your kind thought - I don't have anything like that set up at the moment though, so the best way to support the channel would be to share my videos with anyone who you think might find them interesting!
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