Physic - Chp6

What are tensile forces?

Forces that produce extension, causing tensile deformation

What are compressive forces?

Forces that shorten an object, causing compressive deformation

What is Hooke’s Law?

For a spring obeying Hooke’s Law the applied force is directly proportional to the extension

F = kx, where F is the force applied, k is the spring constant, and x is the extension

How can you determine force constant (k) from a graph?

Finding the gradient of a force-extension graph

What does the area under a force vs extension graph show?

Work done in stretching the spring

What are equations for elastic potential energy?

E = ½ Fx

E = ½ kx²

Define stress

Stress (σ) is the force per unit of cross-sectional area

What are the units of stress?

Pascal (Nm^-²)

Define Strain

Extension per unit length (ε)

What are units of strain?

It has no units

Draw a stress vs strain graph for a typical brittle material

Straight line - obeys Hooke’s law

Doesn’t deform plastically so when stress reaches a certain point the material snaps

Draw a stress vs strain graph for a typical rubber material

Behaves elastically, so returns to original length when load is remove

Less energy released is when rubber is unloaded than the work done to stretch the rubber as some of the EPE is converted to heat (equal to area of hysteresis loop)

Draw a stress vs strain graph for polythene

Behaves plastically, applying stress stretches it to a new shape, is ductile