# Hookes Law

hi, im a student 18 years of age, im currently starting my first year of physics, and ive got an exam coming up, on mechanics, materials and waves

i cant seem to get a grip on hookes law, could someone explain it plz?

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Hi there,

The Hookes law simply models the extension of a spring under a load. If you have a spring that follows this law, then it simply says that the force applied to the spring will extend the spring. If you double this force, you double the extension of the spring.

Cheers

A spring that obeys Hooke's law, when displaced from its equilibrium position by a distance $$\Delta x$$, exerts a force which acts to compress the spring if it has been stretched or vice versa with magnitude $$F=k \Delta x$$ where k is the spring constant. The point is that the force directed towards the equilibrium point increases linearly with displacement.

thanks very much for that.

but how would you calculate the constant k

and what about the rubber not obbeying hookes law. when i was doing a past paper that is one of the questions that actually came up, i could slighty figure it out but other wise i was completly lost

Hi there,

Elastic might follow Hookes' law. To find out, apply a certain force to the spring/rubber and measure the deformation. By doubling the force applied to it, verify that the elongation double also. If so, then you device follows Hookes' law.

Cheers

Andy Resnick
thanks very much for that.

but how would you calculate the constant k

and what about the rubber not obbeying hookes law. when i was doing a past paper that is one of the questions that actually came up, i could slighty figure it out but other wise i was completly lost
The easiest way to measure 'k' (especially for a spring) is to hang weights off one end; plotting mg versus the change in length gives (approximately) a line, the slope of which is 'k'.

Most materials do not obey Hooke's law (it's a linear approximation). Non-linear theories of elasticity are much more complex.

thanks very much for that.

but how would you calculate the constant k

and what about the rubber not obbeying hookes law. when i was doing a past paper that is one of the questions that actually came up, i could slighty figure it out but other wise i was completly lost
Because of its polymetric structure rubber does not obey Hooke's law.It stretches easily at first because the polymer chains are being straightened but once straightened it becomes harder to stretch because the molecules themselves are being separated.Rubber also displays something called hysteresis and recovers by a different route when it is unloaded.