Definitions

1. Breaking Stress

• Definition: The maximum stress that a material can withstand before it fails or breaks.
• Explanation: This threshold is critical in engineering, as exceeding it causes materials to fracture. Engineers use this value to ensure structures can support their intended loads safely.

2. Brittle

• Definition: A material property where the material exhibits minimal strain before it fractures.
• Explanation: Brittle materials, like glass or ceramic, crack rather than deform under stress. They lack the elasticity to absorb impact, making them suitable for uses where rigidity is essential.

3. Centre of Mass

• Definition: The point in an object where all of its mass can be considered to act.

4. Conservation of Energy

• Definition: Energy cannot be created or destroyed, only transferred or transformed.
• Explanation: This principle underpins all physics. For example, in a pendulum, potential energy at the highest point is converted into kinetic energy at the lowest point.

5. Conservation of Momentum

• Definition: The total momentum of a closed system remains constant unless acted upon by external forces.

6. Couple

• Definition: A pair of equal but opposite forces acting parallel but along different lines, creating rotation without translation.

7. Density

• Definition: The mass per unit volume of a material, typically in $kg/m³$.
• Formula: $\rho = \frac{m}{V}$

8. Efficiency

• Definition: The ratio of useful output energy to input energy in a system.
• Formula: $\text{Efficiency} = \frac{\text{Useful Output}}{\text{Total Input}} \times 100\%$
• Explanation: Efficiency measures how well a system converts energy. A 100% efficient machine would have no energy loss, which is ideal but practically impossible.

9. Elastic Behaviour

• Definition: When a material returns to its original shape after the removal of a deforming force.

10. Elastic Collision

• Definition: A collision where the total kinetic energy of the system is conserved.

11. Elastic Limit

• Definition: The maximum force that can be applied to a material without causing permanent deformation.
• Explanation: If the force exceeds the elastic limit, the material will no longer return to its original shape. Beyond this point, plastic deformation begins.

12. Elastic Strain Energy

• Definition: The energy stored in an object when it's stretched or compressed within its elastic limit.
• Formula: Can be calculated from the area under a force-extension graph up to the elastic limit.

13. Equilibrium

• Definition: A state where all the forces and moments acting on an object are balanced, resulting in no acceleration.

14. Hooke's Law

• Definition: The extension of an elastic material is directly proportional to the applied force, up to the material's limit of proportionality.
• Formula: $F = kx$, where $k$ is the spring constant and $x$ is the extension.

15. Impulse

• Definition: The change in momentum resulting from a force acting over a time interval.
• Formula: $\text{Impulse} = F \Delta t = \Delta p$
• Explanation: Impulse is crucial in collisions, where the force over time changes an object's momentum.

16. Inelastic Collision

• Definition: A collision where kinetic energy is not conserved, though momentum is.

17. Moment

• Definition: The turning effect of a force, equal to the force multiplied by the perpendicular distance from the pivot.
• Formula: $\text{Moment} = F \times d$

18. Momentum

• Definition: The product of an object's mass and velocity, indicating its motion quantity.
• Formula: $p = mv$
• Explanation: Momentum is conserved in a closed system, making it vital in understanding collisions.

19. Newton's First Law

• Definition: An object will remain at rest or move at a constant velocity unless acted upon by a resultant force.

20. Newton's Second Law

• Definition: The acceleration of an object is proportional to the net force acting on it and inversely proportional to its mass.
• Formula: $F = ma$

21. Newton's Third Law

• Definition: For every action, there is an equal and opposite reaction.

22. Plastic Behaviour

• Definition: Permanent deformation of a material after the force is removed, beyond the elastic limit.

23. Principle of Moments

• Definition: For equilibrium, the sum of clockwise moments around a pivot must equal the sum of anticlockwise moments.

24. Scalar

• Definition: A quantity with only magnitude and no direction, like mass or temperature.

25. Spring Constant ($k$)

• Definition: A measure of a spring's stiffness, indicating the force required for a unit extension.
• Explanation: Stiffer springs have higher spring constants, meaning they resist stretching more.

26. Stiffness

• Definition: How resistant a material is to being stretched or deformed.
• Explanation: High-stiffness materials don't deform easily, which is important in applications requiring rigidity.

27. Tensile Strain

• Definition: The ratio of an object's extension to its original length, dimensionless.
• Formula: $\text{Strain} = \frac{\Delta L}{L}$

28. Tensile Stress

• Definition: The force per unit area experienced by an object when subjected to stretching forces.
• Formula: $\text{Stress} = \frac{F}{A}$
• Unit: Pascals ($Pa$)

29. Terminal Speed

• Definition: The maximum speed of an object when resistive forces equal the driving force, resulting in zero acceleration.

30. Vector

• Definition: A quantity with both magnitude and direction, such as velocity or force.

31. Young's Modulus ($E$)

• Definition: A measure of a material's stiffness, calculated as the ratio of stress to strain.
• Formula: $E = \frac{\sigma}{\epsilon}$, where $\sigma$ is stress and $\epsilon$ is strain.
• Unit: Pascals ($Pa$)
• Application: Used to characterise materials; higher Young's modulus means a material is less elastic.