Hooke's law

You see that different masses   hanging from the same spring produce different changes in the spring length L. We will study the relation between m  and DL 

What does happen when we hang a mass to a spring?
We  apply to the spring a force Fw = mg directed downward (the weight of the mass ).
When the mass rests in equilibrium the spring must produce a balancing force directed upward (we call it elastic force Fe)  Fw = - Fe
To study the relation between mg  and DL is equivalent to study the the relation between Fe and DL 
(there is only a change of sign)

We hang a mass m to a spring ,using a sonar to measure the changes of the spring length..
We will study the relation between m and DL

By repeating the measurement with different masses we obtain several pairs of values that may be traced on a plot. We may observe that the experimental points lay on a straight line.

By repeating the experiment with a different spring we obtain a similar plot where only the slope is different.

The slope of the fitting line depends only on the type of spring.
A spring is normally characterized by the force needed to produce unitary change in its length, a parameter that is named “elastic constant k” of the spring. In other words: k= DL/m. 
 

[   Close window  ]