Forces & Elasticity Flashcards
All 18 cards in this deck
Why does stretching, bending or compressing a spring require more than one force?
A single force would simply make the spring move; two opposing forces (e.g. the weight pulling down and the support pulling up) are needed to change its shape.
What is the difference between elastic and inelastic distortion?
Elastic: the object returns to its original shape when the forces are removed. Inelastic: it stays permanently changed in shape.
What is meant by the limit of proportionality of a spring?
The point beyond which extension is no longer directly proportional to the force, so the force–extension graph stops being a straight line.
What is the equation linking force, spring constant and extension, with units?
; force in N, spring constant in N/m, extension in m.
True or false? A force–extension graph that is a curve shows force is directly proportional to extension.
False. A curve is a non-linear relationship; directly proportional gives a straight line through the origin.
What is the equation for the energy transferred in stretching a spring, with units?
; energy in J, spring constant in N/m, extension in m.
How can the work done in stretching a spring be found from its force–extension graph?
It is the area under the graph. For a straight line through the origin, work done = ½ × force × extension (J, with force in N and extension in m).
True or false? Doubling the extension of a spring doubles the energy stored in it.
False. Energy depends on , so doubling the extension gives four times the energy.
In the spring core practical, how is the extension of the spring found from ruler readings?
extension = stretched length − original length, with both lengths read from the ruler in the same unit (convert to m before using F = k × x).
In the spring core practical, how should the position of the end of the spring be read against the ruler?
Use a pointer (or set square) against the ruler and read at eye level, to avoid parallax error.
Give two improvements to the procedure of the spring core practical, other than avoiding parallax.
Use a ruler with millimetre divisions; add more weights to increase the range (also: interim values of weight, move the ruler closer to the spring, repeat and average).
When a spring is compressed by adding more and more weights, why does the reduction in length eventually reach a limit?
The coils are pushed together/touching, so the spring is fully compressed and cannot get shorter.
On a force–extension graph with force on the -axis and extension on the -axis, what does the gradient of the straight-line section represent?
The spring constant , in N/m.
On a force–extension graph for a rubber band, what is different about the unloading line compared with the loading line?
The unloading line does not go through the same points as the loading line.
True or false? For a spring stretched within its limit of proportionality, the loading and unloading lines on a force–extension graph lie on the same straight line.
True. The spring's graph has only one line, passing through the same points both ways.
What is the elastic limit of an object?
The point beyond which the object no longer returns to its original shape when the forces are removed. It stays permanently distorted.
How does the spring constant of a stiffer spring compare with that of a less stiff spring?
It is larger: a stiffer spring needs a bigger force for each metre of extension.
When a spring is distorted elastically, how does the work done on it compare with the energy in its elastic potential energy store?
They are equal: all the work done is stored as elastic potential energy.