Year 12s: what will be the first way you research your future options? >>

M3: SHM

Maths&physics

what would be the amplitude? we've stretched it so that the RHS is smaller than it's natural length.

Screenshot 2019-04-05 at 09.32.52 copy.jpg277.4KB

Reply 1

mqb2766

Original post by Maths&physics

what would be the amplitude? we've stretched it so that the RHS is smaller than it's natural length.

IIt's a spring not a string. The natural length of a single spring would be the center of the resulting SHM.

Reply 2

old_engineer

The question says springs not strings.

Reply 3

Maths&physics

Original post by mqb2766

IIt's a spring not a string. The natural length of a single spring would be the center of the resulting SHM.

brilliant! how did you know I misread the word spring for string?!

"The natural length of a single spring would be the center of the resulting SHM." what do you mean?

Reply 4

Maths&physics

Original post by old_engineer

The question says springs not strings.

Original post by mqb2766

IIt's a spring not a string. The natural length of a single spring would be the center of the resulting SHM.

that's superb that you've both noticed from my misunderstanding that I've read spring for string, without my saying it!

but how am I to know that the resulting motion won't go beyond their extensions and give a larger amplitude than the existing extension?

Reply 5

mqb2766

It's the raison detre of a spring. The force is zero at the unstretched natural length. Shorter it pushes, longer it pulls. Here you have two springs. The center is where the forces cancel.

Original post by Maths&physics

brilliant! how did you know I misread the word spring for string?!

"The natural length of a single spring would be the center of the resulting SHM." what do you mean?

Reply 6

Maths&physics

Original post by mqb2766

It's the raison detre of a spring. The force is zero at the unstretched natural length. Shorter it pushes, longer it pulls. Here you have two springs. The center is where the forces cancel.

the centre is where the forces are balanced/equal? but how do I know the amplitude will remain the same as the extension?

Reply 7

mqb2766

The initial condition has zero velocity. It is physically impossible to deviate more than this from the center point in the subsequentsmotion. Otherwise you're getting energy for free.

(edited 5 years ago)

Reply 8

Maths&physics

Original post by mqb2766

The initial condition has zero velocity. It is physically impossible to deviate more than this from the center point in the subsequentsmotion. Otherwise you're getting energy for free.

ok, but the spring on the LHS is compressed (gone beyond its natural length) before it's released, so why wouldnt that effect its subsequent motion - I guess the answer is no, but why?

(edited 5 years ago)

Reply 9

mqb2766

The first part asked you to show that the motion is SHM, you must have considered both forces or springs acting on the body? From then on, you should not really care about what happens to the spring individually?

Original post by Maths&physics

ok, but the string on the LHS is compressed (gone beyond its natural length) before it's released, so why wouldnt that effect its subsequent motion - I guess the answer is no, but why?