materials, hook's law and young modulus Flashcards
what is density?
mass per unit volume of an object
what is lead more dense than?
aluminium
what is sea water more dense than?
tap water
how do you find out how much more dense one substance is compared to another
- we can measure the mass of equal volumes of the two substances.
- The substance with the greater mass in the same volume is more dense
will objects made from low density materials have a low mass or a high mass?
low mass
what are the units for density
kg/ms^3
equation for density
d=m/v
how can you calculate volume of object if not given directly?
find volume of the shape the object is.
for example if object is sphere use sphere volume equation
density of aluminium in g/ms^3
2.73
density of copper in g/ms^3
8.94
what does density of a material mean?
The density of the material is the amount of substance that is packed inside the volume of the substance. The density of the material is generally lowest in its gaseous state, greater in the liquid state, and greatest in the solid state.
can dense materials be easily compressed?
no
what is deformation?
changing shape of an object
what makes an object deformed?
In order for an object to be deformed, a pair of equal and opposite forces must be applied to it.– So, by definition whenever forces are applied to an object, the object is deformed.
can some deformations return to their original shape?
yes if the force is removed
what is elastic deformations?
Once the altering force has been removed from a deformed object, the object springs back to its original for most deformations are elastic.
what is plastic deformations?
Once the altering force has been removed from a deformed object, the object remains permanently deformed
what are tension forces?
– Equal and opposite forces causing extension in an object.
what are compressive forces?
Equal and opposite forces causing compression of an object
what is hookes law?
Hooke’s Law is a principle in physics that states the force F needed to extend or compress a spring by some distance x is proportional to that distance
hookes law equation
f=kx
- F is the force producing the extension.
- x is the extension.
- k is the force constant (or spring constant)
Nm^-1
what can hookes law also tell us?
tells us the stiffness (toughness)of the spring.
what type of deformations does hookes law apply to?
only applies to elastic deformations.
according to hookes law what is the force required to extend or compress a string by a distance directly proportional to?
- According to Hooke’s law, the force required to extend or compress a spring by a certain distance is directly proportional to that distance.
- Hooke’s law is the linear relationship of displacement on stretching.
what is stress?
Stress refers to the internal resistance of a material to deformation. It is the force applied per unit area
what is the restoring force?
The restoring force is a force that acts to bring a body to its equilibrium position.
what does the spring constant mean?
- Can be used to describe
the stiffness of a spring. - Can be found from the
gradient of a force-extension graph
what are the uses of hookes law?
- extension of springs
- Compressions as well as extensions
- Atom behaviour in solids
- Wires under tension or compression
- Anything which can be extended elastically
equation for stress?
F/A
f- restoring force
a - area
pascals (N/m^2)
what is strain?
- The ratio(proportion) of the change in the configuration (i.e. shape, length, or volume) to the original configuration of the body is called strain.
- The strain definition defines it as the amount of deformation experienced by the body in the direction of force applied, divided by the original dimensions of the body.
equation for strain?
extension/orginal length
what are the units for strain?
unitless
how does stress cause strain?
- How much strain is caused depends on the stiffness of the object.
- With a stiff material like iron a large stress will only produce a small strain.
- But with a soft material like rubber a small stress is enough to produce a large strain
what is the relationship between stress and strain
directly proportional
when does hookes law fail?
- Hooke’s Law, which states that the force exerted by a spring is directly proportional to its displacement, is an idealized law that holds true for many materials within their elastic limit.
- However, it fails to accurately describe the behaviour of materials beyond this limit
what does hookes law assumes
Hooke’s Law assumes that materials will return to their original shape and size once the external force is removed
what happens when a material undergoes plastic deformation?
- many materials, especially those subjected to high forces or extreme conditions, may display permanent changes in shape.
- Once a material undergoes plastic deformation, it does not follow Hooke’s Law upon unloading.
when is hookes law applicable to?
- Hooke’s Law is applicable only within the elastic limit of a material.
- Beyond this limit, materials can experience permanent deformation or even break.
what is simple harmonic motion
periodic motion an object experiences due to a restoring force whose magnitude is directly proportional to the distance of the object from an equilibrium position and acts behind the equilibrium position
where is SMH commonly used and found?
used in the oscillatory (swing) motion of objects.
commonly found in springs
what do springs have that define their stiffness (toughness)
Springs have inherent “spring constants” that define their stiffness(Toughness).
according to _____ law, the _____ required to _______ or _______ a spring is __________ to the length stretched
According to Hooke’s law, the force required to compress or extend a spring is proportional to the length stretched.
what is potential energy?
Potential energy is the energy an object has by feature of its position above the surface of the Earth.
Potential energy is the stored energy of position possessed by an object.
what is spring potential energy/ elastic potential energy?
The energy stored in a compressible or stretchable object is referred to as spring potential energy.
equation for spring potential energy?
-kx^-2
what are the limitations of hookes law
Hooke’s Law has a limitation in that it is only applicable under the elastic limit of any material, which means that material must be perfectly elastic in order to obey Hooke’s Law.
disadvantages of Hooke’s law
- Hooke’s Law is only applicable in the elastic region after that it fails.
- Hooke’s Law produces accurate results only for solid bodies with small forces and deformations.
- Hooke’s Law is not a general rule.
young modulus is the relationship between what 2 things?
stress and strain
what happens when a certain load is added to a rigid material
it deforms
what is elasticity
When the weight is withdrawn from an elastic material, the body returns to its original form, this property is called Elasticity
what type of young modulus do elastic bodies have?
Elastic bodies have a steady linear Young’s modulus.
definition of Youngs modulus
Young Modulus is the property of the material which allows it to resist the change in its length according to stress applied to it.
stress is defined as …
force applied per unit length of the object
strain is defined as…
change in shape or length of the object with respect to its original length
what happens to a solid object when a load is applied to it?
changes shape and deforms
what is the elastic property of the object
When the force is applied to an object it changes its shape and as soon as the force is removed from the object it regains its original position. This is called the elastic property of the object.
a solid with a low Youngs modulus value is ______
elastic
a solid with his Youngs modulus value is _____
inelastic /stiff
what graph can be used to find Youngs modulus
stress-strain graph
(gradient is Youngs modulus)
what is elastic limit?
force above which a material will be permanently deformed
factors affecting Youngs modulus
- larger YM value larger the force required to change length
- nature of material of the object
-does not depend on dimensions of object - YM decreases with an increase in temperature
- YM of elasticity of perfectly inflexible body is infinite
