Physics Chapter 7: Matter and Materials

 PHYSICS DEFINITION:

Density: Density is mass per unit volume.

Pressure: Normal (or perpendicular) force acting per unit cross-sectional area.

Archimedes’ Principle: Upthrust acting on body is equal to the weight of the liquid or gas that it displaces.

Hooke’s Law: Provided the elastic limit is not exceeded, the extension of an object is proportional to the applied force (load).

Strain: Extension per unit length.

Stress: Force per unit cross-sectional area that acts at right angles to a surface.

Young Modulus (of a material): Stress in the material divided by the strain.

 

PHYSICS KEYWORD LIST:

Compressive: Describes a force that squeezes and shortens an object.

Tensile: Associated with tension or pulling; for example, a tensile force.

Extension: Increase in the length of a material from its original length.

Spring Constant: Force per unit extension for a spring; unit is N/m.

Elastic Deformation: Object that returns to its initial length when the force is removed has deformed elastically.

Plastic Deformation: Object that does not return to its initial length when the force is removed is deformed permanently – it has deformed plastically.

Limit of Proportionality: Point beyond which extension (of a spring) is no longer proportional to the force.

Elastic Limit: Value of stress beyond which an object (such as spring) will not return to its original dimensions.

Elastic Potential Energy (Strain Energy): Energy stored in a body due to a change in its shape.

Work done: Product of the force and the distance moved in the direction of the force; the area under a force-extension graph.

 

PHYSICS CHAPTER WISE SUMMARY:

Density is defined as the mass per unit volume of a substance: density = mass/volume.

Pressure is defined as the normal force acting per unit cross-sectional area: pressure = normal force/cross-sectional area.

Pressure in a fluid increases with depth: P = pgh.

Upthrust on an object in a fluid is given by F =pgV (Archimedes’ Principle).

Hooke’s Law states that the extension of a material is directly proportional to the applied force, provided the limit of proportionality is not exceeded. For a spring or a wire, F = kx, where k is the force constant. The force constant has units of N/m.

Stress is defined as: Stress = Force/ Cross-sectional Area.

Strain is defined as: Strain = Extension/ Original Length.

To describe the behaviour of material under tensile and compressive forces, we have to draw a graph of stress against strain. The gradient of the initial linear section of the graph is equal to the Young modulus. The Young modulus is an indication of the stiffness of the material.

The Young modulus E is given by: E = Stress/Strain. Unit pascal (Pa) or N/m^2.

The area under a force – extension graph is equal to the work done by the force.

For a spring or a wire obeying Hooke’s law, the elastic potential energy E is given by: E = ½ Fx = ½ kx^2.

 

PHYSICS IMPORTANT NOTES:

Density = Mass/Volume (p = m/v)

Pressure = Normal Force/ Cross-sectional Area (P = F/A)

Change in pressure = density x acceleration due to gravity x depth (P=pgh)

Upthrust = pgV = Weight of liquid displaced

Spring constant = force/extension (k= F/x)

Strain = extension/original length

Stress = Normal Force/ Cross-sectional Area

E = ½ Fx = ½ kx^2