# A level Physics SHM/Circular Motion

Thread starter 3 years ago
#1
https://umutech.net/PeriodicMotionII.pdf

I need help with Question 7(a) which asks for an explanation as to which direction the pointer moves during circular motion.
It makes sense that it would point towards A but I don't understand how to explain in terms of the tensions in the springs. The mark scheme and examiner report are a little vague
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3 years ago
#2
Equal and opposite forces I think, but I imagine this should've been a criteria to score on the mark scheme, which it isn't ...
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3 years ago
#3
Or, essentially the point is not part of the car since it is attached via springs, so essentially it is it's own free body. Therefore, when the car is in circular motion, the pointer moves to the right due to the difference in motion between the car (kind of like when you're sat in a car and the car turns round a corner. If you're sat on the same side as the corner, you feel like you're are being pushed against the car door because you're body still has forward momentum whereas the cars momentum has changed since it is now turning).

So when the pointer moves to the right, one spring is compressed and the other must stretch (Equal and opposite forces must co-exist).
Last edited by BTAnonymous; 3 years ago
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Thread starter 3 years ago
#4
(Original post by BTAnonymous)
Or, essentially the point is not part of the car since it is attached via springs, so essentially it is it's own free body. Therefore, when the car is in circular motion, the pointer moves to the right due to the difference in motion between the car (kind of like when you're sat in a car and the car turns round a corner. If you're sat on the same side as the corner, you feel like you're are being pushed against the car door because you're body still has forward momentum whereas the cars momentum has changed since it is now turning).

So when the pointer moves to the right, one spring is compressed and the other must stretch (Equal and opposite forces must co-exist).
Yeah this makes sense to me now, thanks
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3 years ago
#5
(Original post by kinghulio)
https://umutech.net/PeriodicMotionII.pdf

I need help with Question 7(a) which asks for an explanation as to which direction the pointer moves during circular motion.
It makes sense that it would point towards A but I don't understand how to explain in terms of the tensions in the springs. The mark scheme and examiner report are a little vague

I don’t really agree with some of the writings from BTAnonmous.

According to circular motion, the net force acting on the mass M in the scale is towards the right. The net force is provided the spring force in the 2 springs.

The spring attached to B is stretched, so this spring exerts a force on the mass to the right.

The spring attached to A is compressed, so this spring exerts a force on the mass to the right. See how the spring force work in the picture below.

As a result, the spring forces exerting on the mass is to the right which provides the net force on the mass to undergo circular motion. And the pointer moves to A.

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Thread starter 3 years ago
#6
(Original post by Eimmanuel)
I don’t really agree with some of the writings from BTAnonmous.

According to circular motion, the net force acting on the mass M in the scale is towards the right. The net force is provided the spring force in the 2 springs.

The spring attached to B is stretched, so this spring exerts a force on the mass to the right.

The spring attached to A is compressed, so this spring exerts a force on the mass to the right. See how the spring force work in the picture below.

As a result, the spring forces exerting on the mass is to the right which provides the net force on the mass to undergo circular motion. And the pointer moves to A.

Hmm, BTA explained in terms of momentum and inertia, but you've explained it more in terms of the actual forces on the springs and circular motion. Thanks for your time I think I get it now, basically its just Newtons 3rd law of motion to figure out which spring compresses and which one stretches so that the resultant on the mass is to the right since the resultant force must be in that direction (right?)
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