Geekzone: technology news, blogs, forums
Guest
Welcome Guest.
You haven't logged in yet. If you don't have an account you can register now.


5209 posts

Uber Geek
+1 received by user: 2119


Topic # 203129 19-Sep-2016 09:50
Send private message

If an object of certain mass in sitting on spring, does the act of it's compressing the spring absorb some of it's weight.

 

For example: - 

 

A) I place an object on a scale and the scale reads 100kg.

 

B) If I place it on a spring (pretend the spring as no mass) and place the assembly on the same scale under the same conditions will it now read less?

 

I realise the mass of the object is unchanged.  I am interested in the downward force acting on the scale.





Mike

Filter this topic showing only the reply marked as answer Create new topic
2864 posts

Uber Geek
+1 received by user: 491


  Reply # 1635712 19-Sep-2016 09:52
Send private message

The scales will show the same weight, ignoring as you say the weight of the spring.




Sony Xperia X running Sailfish OS. https://sailfishos.org The true independent open source mobile OS 
Samsung Galaxy Tab S3
Nokia N1
Dell Inspiron 14z i5


4644 posts

Uber Geek
+1 received by user: 2153

Trusted
Subscriber

  Reply # 1635714 19-Sep-2016 09:53
2 people support this post
Send private message

The weight is still 100kg plus the mass of the spring. All the forces have to balance. If they don't, then the object isn't sitting on the scale - it's accelerating in some direction.





iPad Air + iPhone SE + 2degrees 4tw!

These comments are my own and do not represent the opinions of 2degrees.


1512 posts

Uber Geek
+1 received by user: 785


  Reply # 1635724 19-Sep-2016 10:15
One person supports this post
Send private message

In the steady state, Salty's statement below is true.

 

When the weight is first put on the spring, the force transmitted is zero (Hooke's Law).  As the spring compresses due to the weight on it, the force transmitted increases from zero to the full weight of the supported weight.

 

SaltyNZ:

 

The weight is still 100kg plus the mass of the spring. All the forces have to balance. If they don't, then the object isn't sitting on the scale - it's accelerating in some direction.

 




5209 posts

Uber Geek
+1 received by user: 2119


  Reply # 1635737 19-Sep-2016 10:46
Send private message

shk292:

 

In the steady state, Salty's statement below is true.

 

When the weight is first put on the spring, the force transmitted is zero (Hooke's Law).  As the spring compresses due to the weight on it, the force transmitted increases from zero to the full weight of the supported weight.

 

SaltyNZ:

 

The weight is still 100kg plus the mass of the spring. All the forces have to balance. If they don't, then the object isn't sitting on the scale - it's accelerating in some direction.

 

 

 

Thanks both.





Mike

524 posts

Ultimate Geek
+1 received by user: 122


  Reply # 1635740 19-Sep-2016 10:52
Send private message

shk292:

 

In the steady state, Salty's statement below is true.

 

When the weight is first put on the spring, the force transmitted is zero (Hooke's Law).  As the spring compresses due to the weight on it, the force transmitted increases from zero to the full weight of the supported weight.

 

SaltyNZ:

 

The weight is still 100kg plus the mass of the spring. All the forces have to balance. If they don't, then the object isn't sitting on the scale - it's accelerating in some direction.

 

 

 

I wonder if a simple test of this would be to place both the spring and the weight on the scales side by side (or possibly zero the scales with just the spring on them).  Note the reading.  Then move the weight from the scales to the spring.  Note new reading.
Am I simplifying it too much or would this work?

 

 





4644 posts

Uber Geek
+1 received by user: 2153

Trusted
Subscriber

  Reply # 1635745 19-Sep-2016 11:02
Send private message

geoffwnz:

 

 

 

I wonder if a simple test of this would be to place both the spring and the weight on the scales side by side (or possibly zero the scales with just the spring on them).  Note the reading.  Then move the weight from the scales to the spring.  Note new reading.
Am I simplifying it too much or would this work?

 

 

 

 

No, that's exactly right. But the answer 100kg only applies to the steady state, i.e. everything has stopped moving. If the mass is still moving - compressing the spring down - then the scale's reading will be lower. As the spring compresses it will push back against the gravitational force imposed by the mass. It pushes back more forcefully as it compresses, approximately linearly, until either they balance, or the spring is fully compressed.

 

If the spring is not fully compressed, the mass will overshoot, and then (assuming everything is moving directly up and down) you end up with a harmonic motion, which will gradually die out due to things like air resistance and imperfect elasticity of the spring.





iPad Air + iPhone SE + 2degrees 4tw!

These comments are my own and do not represent the opinions of 2degrees.


2924 posts

Uber Geek
+1 received by user: 835

Subscriber

  Reply # 1635747 19-Sep-2016 11:05
Send private message

If the scale shows less than the total weight - hey presto, you've invented an anti-gravity device!


1918 posts

Uber Geek
+1 received by user: 375

Subscriber

  Reply # 1635870 19-Sep-2016 13:48
Send private message

eracode:

 

If the scale shows less than the total weight - hey presto, you've invented an anti-gravity device!

 

 

Could make a fortune with thatsmile


Filter this topic showing only the reply marked as answer Create new topic

Twitter »

Follow us to receive Twitter updates when new discussions are posted in our forums:



Follow us to receive Twitter updates when news items and blogs are posted in our frontpage:



Follow us to receive Twitter updates when tech item prices are listed in our price comparison site:



Geekzone Live »

Try automatic live updates from Geekzone directly in your browser, without refreshing the page, with Geekzone Live now.



Are you subscribed to our RSS feed? You can download the latest headlines and summaries from our stories directly to your computer or smartphone by using a feed reader.

Alternatively, you can receive a daily email with Geekzone updates.