4.5.3 Forces and Elasticity

Question 1

Extension:

Answer 1

the increase in length to the unloaded original length

Question 2

Extension =

Answer 2

extended (overall) length - original (unloaded) length

Question 3

Hooke’s Law:

Answer 3

• the extension of an elastic object is directly proportional (straight line through the origin) to the force applied (provided that the limit of proportionality is not exceeded)
• any % change in one variable leads to a % change in the other variable

Question 4

F (Force/N) =

Answer 4

ke (spring constant (N/m) x extension/m)

Question 5

What is the spring constant?

Answer 5

• how firm or elastic the material is
• the higher it is the firmer the spring is
• the lower it is the more elastic the spring is

Question 6

For an object to be elastic what does it need to be able to do?

Answer 6

elastically deform

Question 7

Elastically deformed:

Answer 7

an object has been elastically deformed if it can go back to its original shape and length when the force is removed

Question 8

Inelastically deformed:

Answer 8

an object has been inelastically deformed if it doesn’t return to its original shape and length when the force is removed

Question 9

What is the relationship between the extension of an elastic object and the force applied?

Answer 9

• the extension of an elastic object is directly proportional to the force applied - there is a straight line that goes through the origin
• -> force ∝ extension
• -> any % change in one variable leads to a % change in another variable
• there is a linear (straight line) relationship between the force and extension because we get a straight line graph
• shows the objects is elastic because when the force is released, extension goes back to 0 (elastically deform)

Question 10

Examples of elastic objects:

Answer 10

• rubber e.g. rubber band, eraser, rubber gloves
• sponge
• car suspension
• face e.g. skin
• muscles
• climbing rope
• bouncy castles
• aircraft wings
• slinky
• tennis ball
• muscles
• playground surface

Question 11

Inelastic material:

Answer 11

• when inelastic material are stretched they don’t return to their original length - inelastic deformation
• certain polymers

Question 12

What is the difference between free body diagrams and force diagrams?

Answer 12

• Free body diagrams only show the forces acting on a particular object and not the other objects its interacting with
• The object the forces are acting on is shown as a circle or square rather than the actual object being sketched out.

Question 13

What is the relationship between force and extension on a rubber band?

Answer 13

• Non-linear relationship between force and extension
• Doesn’t obey Hooke’s law as the force and extension aren’t directly proportional as there isn’t a straight line going through the origin

Question 14

How do you find the spring constant on a force extension graph?

Answer 14

Find the gradient