Hooke's Law 2

Question 1

how is steel simply produced

Answer 1

by mixing iron with small quantities of carbon

Question 2

what do the properties of steel depend on

Answer 2

• the percentage of carbon in it

- the heat treatment of the steel

Question 3

what does the force extension graph for mild steel look like (steel containing below 0.25% carbon)

Answer 3

• it starts of linearly with a high gradient
• then at around 40N begins making a jerking pattern up and down
• then eventually begins to slightly increase
• before beginning to slightly decrease and break at 40N

Question 4

what does the force extension graph for high-carbon steel look like

Answer 4

• it is linear with a high gradient almost all the way

- until at the very end the line plateaus quickly and breaks

Question 5

what does the force extension graph for a rubber band look like

Answer 5

• it stretches very easily at first
• making a smooth line with a low gradient
• then it becomes stiff and hard to stretch
• causing the line to smoothly but quickly increase its gradient

Question 6

why does rubber band have this initial ease of stretching where large extensions are caused by small forces

Answer 6

• rubber is a polymer
• so it contains long chains of atoms that are normally tangled in a disordered fashion
• relatively small forces are needed to untangle these molecules and therefore cause a large extension

Question 7

when does the gradient of rubbers force-extension graph begin to change

Answer 7

when the chains composing the polymer are fully extended

Question 8

why does rubbers force-extension gradient then get very large

Answer 8

• the additional forces are needed to stretch the bonds between atoms
• causing smaller extensions for given loads

Question 9

why are force-compression graphs much harder to compile for metals

Answer 9

• in force-extension long thin samples of the metal can be extended by a large amount with relatively small tensile forces
• but with compression shorter and thicker samples are needed
• which require much larger forces to produce measurable compressions

Question 10

what is the solution to compression experiments requiring much larger forces

Answer 10

large hydraulic presses are used

Question 11

what special equipment would be needed to carry out a practical to draw a force-compression graph

Answer 11

• a displacement sensor and display unit

- which shows the length of compression of the object corresponding to the force exerted on it

Question 12

what is potential energy

Answer 12

the ability of an object to do work by virtue of its position or state

Question 13

what is elastic potential or elastic strain energy

Answer 13

• the ability of a deformed material to do work

- as it regains its original dimensions

Question 14

what are the energy transfers of a catapult as its pulled back with a projectile in it

Answer 14

• the work done stretching the rubber band is transferred to its elastic potential energy stores
• when released this energy is transferred to the kinetic energy of the projectile

Question 15

what equation would you use to calculate the work done on the rubber band

Answer 15

W = Fx

Question 16

how would you calculate the work done on a band from a force-extension graph

Answer 16

• the area under the line

- as Fx = W