Force extension graphs

Question 1

What is the gradient of a force extension graph?

Answer 1

The stiffness of the spring

Question 2

What do i need to be able to analyse on a force extension graph

Answer 2

• limit of proportionality
• elastic limit (past this point material will be permanently stretched)
• area affected by hooke’s law
• yield point

Question 3

How do we know hooke’s law is obeyed by looking at the graph?

Answer 3

There should be straight line to represent direct proportionality =

Question 4

What is the area of a a force extension graph/?

Answer 4

elastic strain energy

Question 5

Before the elastic limit what is the work stored as?

Answer 5

all the work done in stretching is stored as elastic strain energy

Question 6

These graphs are specific to what?

Answer 6

the object being tested rather than the material it is made out of and its dimensions

Question 7

What is an unloading line?

Answer 7

a line which shows the extension decreasing , which is parallel to the loading line as k stays constant (so the same gradient)

Question 8

If the unloading line doesn’t go through the origin what does that mean?

Answer 8

The object has been permanently stretched

Question 9

What is the area between the loading and unloading line>?

Answer 9

the work done to permanently deform the material =

Question 10

What is the yield point?

Answer 10

The point at which the object will not contract at all after the force is removed. Beyond this point the wire is fully plastic and can be pulled like a modelling clay until it breaks.