Hooke's Law

Question 1

what does hookes law simply state

Answer 1

• that the extension of a spring is directly proportional to the force applied to the spring
• up to a given load

Question 2

what is the equation for hookes law

Answer 2

• F = k delta x
• F = force
• k = stiffness of the spring
• delta x = extension

Question 3

what does a graph of force against extension usually look like according to hookes law

Answer 3

• there is a linear region when the spring is still coiled
• this indicates that the extension is directly proportional to the force applied
• then the line begins to droop downwards as the extension increases disproportionately
• this is due to the spring losing its springiness when it passes the limit of proportionality

Question 4

what is k called

Answer 4

the spring constant

Question 5

before the limit of proportionality, when the load is removed from the wire, how do we know that the spring is elastic

Answer 5

because it returns to its original length or shape when the deforming force is removed

Question 6

how does elasticity work on an atomic level with a copper wire

Answer 6

• the atoms in a solid are held together by bond which behave like springs between the particles
• when the wire is stretched, atomic separation increases
• in the elastic region the atoms return to their original positions when the deforming force is removed

Question 7

what is the elastic limit of a material

Answer 7

the point in which it will stop being elastic

Question 8

what has happened to a material that has passed its elastic limit

Answer 8

it has undergone permanent deformation

Question 9

what is a plastic material

Answer 9

a material that retains its shape after the deforming force is removed

Question 10

what other point is there on a force extension graph past the limit or proportionality and what does it show

Answer 10

• the yield point

- it is the point where the wire yields and wont contract at all when the load is removed

Question 11

what is the difference between the elastic limit and the yield point

Answer 11

• past the elastic limit the wire / spring can still shorten in length but not back to its original dimensions
• whereas with the yield point it wont contract at all as it is now plastic

Question 12

what happens when you unload and reload a wire that is currently in its plastic phase as it has passed the yield point

Answer 12

when unloaded and reloaded the wire regains its springiness and has the same stiffness as before

Question 13

why is this property important for metals in manufacturing

Answer 13

• a piece of metal can be moulded into different shapes

- after the deformation the stiffness and elasticity of the metal is regained so further processing is possible