Materials

Hooke's Law

• Extension is proportional to force so F=kx
• K is the force constant and as units N/m
• Works for compressive forces as well as tensile forces
• Doesn't just apply to springs - most other materials obey it up to a point
• Works for compressive forces as well as tensile forces
• Doesn't just apply to springs - most other materials obey it up to a point
• 
• Caption: If in series , K of entire set up is 2K. If parallel, k/2.

Elastic and plastic stretches

• Elastic deformation up to its elastic limit and plastic deformation beyond it.
• Elastic deformation - When the material returns to its original shape once the force is removed. When the material is put under tension, atoms of the material are pulled apart from one another. They can move relative to their equilibrium positions, without changing position in the material and once the load is removed, they return to their equilibrium distance apart.
• Plastic deformation = the material is permanently stretched.
• Plastic deformation - Some atoms in the material move relative to one another and when the load is removed, they do not return to their original position.

Slide 3