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### Course: Class 11 Physics (India)>Unit 13

Lesson 2: Shear and bulk stress

# Bulk stress and strain

Let's explore the concept of bulk stress and bulk strain. Created by Mahesh Shenoy.

## Want to join the conversation?

• Bulk stress is F/(initial area) or F/(area after compression)?
• The surface area is the same before and after compression when under hydraulic pressure, material is not 'magically' formed or destroyed once compressed.
But, this depends on the material's tensile stress and strain. Consider a balloon's surface area, it will increase when blowing it up because of the material's elasticity or tensile strain (proportional to tensile stress), as you blow into it, the material stretches.

If wrong, lemme know,
hope this helps,
onward!
(1 vote)
• when pressure is applied on to the stone underwater does the stone get permanently deformed or is it temporary and when the stone is taken out it regains its original shape ?
• so at "" are we considering only the magnitude of the forces,because force is vector quantity right? so, the bulk stress cannot be eqaul to the pressure because they are completely opposite to each other
(1 vote)
• I guess we're considering the forces as vectors here, wherever there is an external force acting per unit area,
there will be deformation(however small), there will be a restorative force developed over that area,
the external force = -restorative force
as net force = 0 as a = 0 (equal in mag. opp. in direction)(Newton's 1st law of motion) when in EQUILIBRIUM
try drawing a free body dia, resolve the (couple)forces into their components, you will find they cancel.

And one more thing, bulk stress, and pressure are scalar quantities.
hope this helps,
if wrong let me know,
Onward!
(1 vote)
• Let's say we have a balloon immersed in water, it exerts pressure due to compression (bulk stress), so, there is a (net) force exerted by the balloon downwards other than its weight => loss in weight is lesser than if object is not compressed, right?
(note that the pressure exerted by water/Liq.∝Bulk Stress is greater on the bottom than the top)

Now, consider Archimedes' principle, wouldn't the weight of displaced water < change in weight of the object?
(1 vote)
• so unlike the earlier strains(longitudinal strain & shear strain ) this one(bulk strain) is different right? because here instead of taking the difference of change, we are taking changed volume..so that's why we are adding minus here....am i right?
(1 vote)
• sir will there be any change in area during compression of volume
(1 vote)