4.5.3 Forces and elasticity

what occurs when applying a force to an object

may cause it to stretch, compress, bend

forces in elastic materials

will always return ti original length or shape if forces acting on them are taken away

why do we need to apply more than one force

so the objects stay still, otherwise they will move when pulled or pushed

if one force applied- forces are not balanced so objects will move instead of changing shape

forces when squishing

2 forces

you apply a force

floor apply upward force

deformed

object changing shape

types of deformation

elastic- returns original shape

inelastic/ plastic - does not quite return to normal shape

extention

increase in length of a spring when it is stretched

natural length of a spring I shorter as the downward force of weight is added

why does the spring not fall down when mass added

solid support exerts an equal but opposite force upward

which is why the spring Dosent fall down when adding mass

it is being perfectly balanced by the support

relationship between mass and extension

increasing mass/ force added proportional increases the extension

F∞e

what is the length of extension dependent on

the particular objects spring constant- tells us how many newtons it would the to stretch the object by 1m

higher spring constant means stiffer material as it requires more force to extend it

elasticity equation (force, spring constant, extension )

F=ke

force, *F*, in newtons, N \n spring constant, *k*, in newtons per metre, N/m

extension/ compression, *e*, in metres, m

spring constant

specific to the object

measure of how firm or elastic the object is

lower spring constant means object is more elastic ∴ easier to stretch

higher spring constant means object is more stiff

elasticity equation (energy)

Ee = ½ke²

* calculate work done in stretching (or compressing) a spring (up to the limit of proportionality) using the equation:

Hookes law

force and extension are directly proportional

all the deformation will be elastic deformation as the force returns to its original shape

on graph straight part of the line is the spring constant

area under curve= energy transferred to the spring Ee

elastic limit

limit of proportionality- graph will start to curve

hookes law no longer applies and the object won’t return to original shape- inelastically deformed

there is lots of extension not a lot of force

what does it mean if graph is just linear

the material is brittle, so snaps instead of stretches after elastic limit