Study Guide
Density - Answer>> mass per unit volume
Density is a SCALAR quantity
Units of density - Answer>> kg m-3
Hooke's Law - Answer>> extension is proportional to the force
applied, up to the limit of proportionality.
Features of graph of force against extension confirming Hooke's
Law - Answer>> straight line, through the origin.
Units of spring constant - Answer>> Nm-1
Springs in series - Answer>> • Both springs experience the
same force F.
• The total extension (of both springs together) is the sum of the
extension of each spring individually.
(Identical) Springs in parallel - Answer>> • The force F applied
to the spring combination is shared across each of the springs
individually (if there are two identical springs, each spring
experiences a force of ½F).
• All springs have the same extension (and equals the extension
for the spring combination).
Elastic limit - Answer>> the maximum amount a material can be
stretched by a force and still return to its original length when the
force is removed.
, Limit of proportionality - Answer>> point beyond which force is
no longer proportional to extension
Elastic behaviour - Answer>> material will return to its original
length (when force removed) with no permanent extension.
Plastic behaviour - Answer>> material will be permanently
extended (when force is removed).
Area under a force/extension graph - Answer>> area under a
graph of force against extension is work done on spring and
hence the energy stored, as it is loaded.
or
area under a graph of force against extension is the work done by
the spring, and hence energy released, as it is unloaded.
Area between the loading and unloading curves of an elastic band
- Answer>> internal energy retained, eg as heat, within the
elastic band
Interpretation of force against extension curves - Answer>>
Derivation of energy stored = ½ FΔL from a graph of force against
extension - Answer>> ΔW=FΔs, so area beneath line from
origin to ΔL represents the work done to compress/extend spring.
• work done (on spring) equals the energy it stores.
• area under graph = area of triangle = ½ base x height, therefore
energy stored = ½ F x ΔL.
Derivation of
energy stored = ½ FΔL - Answer>> • Energy stored in a
stretched spring = work done stretching the spring.