In this blog, we are going to learn about basic mechanical engineering concepts and terms used widely. These are the basic building blocks of physics which are used widely in the field of mechanical engineering. The terms like force, acceleration, velocity, and vibrations are the basics of any engineering.
Force:
Force is a push or pull on an object causing it to change its velocity. It is a vector quantity. It is an external agent that causes a change in the velocity of the object. SI unit of force is Newton(N).
Contact Force
- Muscular Force
- Mechanical Force
- Frictional Force
Non-Contact Force
- Gravitational Force
- Electro Static Force
- Frictional Force
Pressure:
Pressure is a force exerted per unit area(F/A). The SI unit is Pascal (Pa) which can be written as N/m2
Types of Pressure
- Atmospheric pressure
- Absolute pressure
- Differential pressure
- Gauge pressure
Velocity:
Velocity is displacement per unit of time in a particular direction. It is a vector quantity.
Often we use speed and velocity interchangeably but both terms are different. Speed is a scaler term with only magnitude and no direction. In the case of velocity magnitude and direction both are present.
Acceleration:
Acceleration is the rate at which velocity changes with time in terms of both speed and direction. It is a vector quantity. The SI unit is m/s2
Types of Acceleration
- Uniform acceleration
- Nonuniform acceleration
Work:
Work is a transfer of energy by a force acting on an object as it is displaced. The SI unit work is Joule (J).
Work is the product of force in the direction of displacement and the magnitude of the displacement.
Energy:
Energy is the ability to do work or to exert force on the object to displace it. It can exist in many forms like,
- Mechanical energy
- Chemical energy
- Thermal energy
- Electrical energy
- Nuclear energy
All forms of energy are either kinetic or potential. It is a quantitative property.
SI unit of energy is Joule (J), equal to 1 Nm.
Friction:
Friction is the force that resists motion between two bodies in contact. The friction formula is f=μN, Where Mu(μ) is the coefficient of friction and N is the normal force.
Types of friction:
- Rolling friction
- Sliding friction
- Static friction
- Fluid friction
- Kinetic Friction
Examples of friction
- Driving a vehicle on the road
- Flying an Aeroplane
- Skating
- Walking
- Writing on notebook
- Applying brakes to stop the vehicle
- Drilling a nail into the wall
Stress:
Stress is force divided by area. The formula for stress is σ=F/A.
SI Unit for stress is N/m2. There are six types of stresses present in engineering: Compression, Tension, Share, Bending, Torsion, and Fatigue.
Strain:
Strain is a measure of the deformation of the material due to stress applied to it. It is the ratio of change in length to original length. It has no unit. Deformation that is applied perpendicular to the cross-section is called normal strain. Deformation that is applied parallel to the cross-section is called share strain.
Types: Tension strain and Compressive strain
Hook’s Law:
Strain is directly proportional to the stress applied to the body within an elastic limit.
F=kx, where F is force, x is an extension in length, and k is a proportionality constant or spring constant.
Stress-Strain curve:
1. Elastic region: Initial linear relationship between stress and strain where material returns to its original shape. It is the region where Hooks’ law applies.
2. Yield point: Stress threshold where the material begins to deform plastically.
3. Plastic region: Non-linear deformation occurs as material undergoes permanent changes.
4. Ultimate tensile strength: Maximum stress material can withstand before breaking.
5. Necking: Localized narrowing of material before failure.
6. Breakdown Point: Stress at which material breaks or fractures.
Newton’s laws of motion:
First Law (Law of Inertia):
An object will remain at rest or continue to move at a constant velocity unless acted upon by an external force.
Second Law (F = ma):
The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. Mathematically, this is expressed as F = ma, where F is the force applied, m is the mass of the object, and a is the acceleration produced.
Third Law (Action and Reaction):
For every action, there is an equal and opposite reaction. This means that whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first.
Static:
Static refers to a state where objects or systems are at rest or in a constant position to time. In static analysis, engineers study the behavior of structures or systems under equilibrium conditions, where the forces acting on them are balanced. Static analysis is crucial for assessing the stability, strength, and integrity of structures, such as buildings, bridges, and mechanical components.
Dynamic:
On the other hand, involves motion or changes over time. Dynamic analysis considers how objects or systems respond to external forces or disturbances and how they move or change in response. This includes studying the acceleration, velocity, and displacement of objects or components subjected to forces or motion. Dynamic analysis is essential in various engineering fields, including mechanical engineering, aerospace engineering, and robotics, where understanding the dynamic behavior of systems is critical for design, optimization, and control.
Vibration:
Vibration is a repetitive motion or oscillation of an object or system about a reference point. It can occur in various forms, from mechanical vibrations in machinery to structural vibrations in buildings and bridges. People can intentionally induce vibration for various purposes, such as in musical instruments or vibrating platforms for exercise, while vibration remains a natural phenomenon.
Types of vibration:
Free or Natural Vibration
Free vibration occurs when a system oscillates or vibrates naturally without any external force applied to it after an initial disturbance. Once the system is set in motion, it continues to vibrate at its natural frequency until external influences or damping effects dissipate the energy.
Forced Vibration
When a system is subjected to an external force or excitation at a specific frequency, forced vibration occurs. Unlike free vibration, the system’s motion is not solely determined by its natural characteristics but rather influenced by the external force driving it. The response of the system to the external excitation can be complex and depends on factors such as the frequency and magnitude of the forcing function.
Damped Vibration
Damped vibration occurs when the energy of a vibrating system gradually dissipates over time due to internal or external damping mechanisms. Damping reduces the amplitude of vibration and can eventually bring the system to rest. Various factors, including material properties, friction, and the presence of damping devices, can cause damping. In mechanical systems and structures, where controlling and reducing vibrations is desirable to prevent fatigue and failure, people commonly encounter damped vibration.
Limits, Fits, and Tolerances
Limits:
It is defined as the maximum and minimum acceptable sizes of a part. They ensure that the part will fit within a specified range of dimensions. For example, a shaft might have a lower limit for diameter to ensure it fits into a corresponding hole, and an upper limit to prevent it from being too large.
Fits:
Fits determine the type of relationship between two mating parts, based on their dimensional tolerances. Various fit types include clearance fit, interference fit, and transition fit.
Clearance fit:
This fit allows for clearance between the mating parts, ensuring easy assembly and disassembly. Manufacturers commonly use it when parts need to move freely relative to each other.
Interference fit:
In this fit, the dimensions of the mating parts overlap, requiring force to assemble them. This tight fit ensures a strong connection and resistance to movement.
Transition fit:
Transition fits fall between clearance and interference fits, providing a compromise between ease of assembly and strength of the connection.
Tolerances:
Tolerances specify the allowable deviation from the nominal dimension of a part. They ensure that parts can be manufactured within acceptable variations while still meeting functional requirements. Tolerances can be expressed as either unilateral (one-sided) or bilateral (two-sided), and they are typically specified using standard symbols and values according to industry standards like ISO (International Organization for Standardization) or ANSI (American National Standards Institute).
Thank you for reading.
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