Section 5: Materials
Density
-The ratio of mass per unit volume, and a property that all materials have.
p = m/v Density (kg m-3) = Mass (kg) / Volume (m3)
The density of material depends on what it is made of. The shape and size of the material doesn’t alter
the density. An object will float on a liquid if it has a lower density than they liquid.
Water has a density of p = 1.00g cm-3. Therefore 1cm3 of water has a mass of 1g.
Hooke’s Law
When a metal wire is supported at the top and a downward force is applied to it. The weight pulls down
at the metal wire up until it stops stretching. At this point it is act equilibrium (equal and opposite forces
are at the support)
The force applied is directly proportional to the extension of the wire (length with force applied – the
original length).
Hooke’s law – F (N) = k(Nm-1) ∆l(m)
K is the stiffness constant that varies depending on the material.
The value of k remains the same, for compressive and tensile forces
Limit of proportionality
When there is a straight line relationship between the force and the extension, it is obeying Hooke’s law.
The gradient of the straight line is the stiffness constant.
Limit of proportionality - The point beyond which the force is no longer proportional to the extension
Elastic limit – Point beyond which the spring can no longer revert back to its original length - Plastic
deformation occurs.
Elastic stretches
If a deformation is elastic, the material returns to its original shape
once the forces are removed. Therefore there is no permanent
extension.
When the material is put under tension, the atoms of the material are
pulled apart from one another. Atoms can move small distances
relative to their equilibrium position in the material. Once the load is removed the atoms return back to
its equilibrium position.
Density
-The ratio of mass per unit volume, and a property that all materials have.
p = m/v Density (kg m-3) = Mass (kg) / Volume (m3)
The density of material depends on what it is made of. The shape and size of the material doesn’t alter
the density. An object will float on a liquid if it has a lower density than they liquid.
Water has a density of p = 1.00g cm-3. Therefore 1cm3 of water has a mass of 1g.
Hooke’s Law
When a metal wire is supported at the top and a downward force is applied to it. The weight pulls down
at the metal wire up until it stops stretching. At this point it is act equilibrium (equal and opposite forces
are at the support)
The force applied is directly proportional to the extension of the wire (length with force applied – the
original length).
Hooke’s law – F (N) = k(Nm-1) ∆l(m)
K is the stiffness constant that varies depending on the material.
The value of k remains the same, for compressive and tensile forces
Limit of proportionality
When there is a straight line relationship between the force and the extension, it is obeying Hooke’s law.
The gradient of the straight line is the stiffness constant.
Limit of proportionality - The point beyond which the force is no longer proportional to the extension
Elastic limit – Point beyond which the spring can no longer revert back to its original length - Plastic
deformation occurs.
Elastic stretches
If a deformation is elastic, the material returns to its original shape
once the forces are removed. Therefore there is no permanent
extension.
When the material is put under tension, the atoms of the material are
pulled apart from one another. Atoms can move small distances
relative to their equilibrium position in the material. Once the load is removed the atoms return back to
its equilibrium position.
