physics

Mechanical joint

Mechanical joint is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Mechanical joint rather than just read about it. In short: A mechanical joint is a section of a machine which is used to connect one or more mechanical parts to another. Mechanical joints may be temporary or permanent; most types are designed to be disassembled.

Key takeaways

Mechanical joint belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mechanical joint to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mechanical joint from memory before moving on to harder problems.

Reference excerpt

A mechanical joint is a section of a machine which is used to connect one or more mechanical parts to another. Mechanical joints may be temporary or permanent; most types are designed to be disassembled. Most mechanical joints are designed to allow relative movement of these mechanical parts of the machine in one degree of freedom, and restrict movement in one or more others.

Pin A pin joint, also called a revolute joint, is a one-degree-of-freedom kinematic pair. It constrains the motion of two bodies to pure rotation along a common axis. The joint doesn't allow translation, or sliding linear motion. This is usually done through a rotary bearing. It enforces a cylindrical contact area, which makes it a lower kinematic pair

Prismatic

A prismatic joint provides a linear sliding movement between two bodies, and is often called a slider, as in the slider-crank linkage. A prismatic pair is also called as sliding pair. A prismatic joint can be formed with a polygonal cross-section to resist rotation. The relative position of two bodies connected by a prismatic joint is defined by the amount of linear slide of one relative to the other one. This one parameter movement identifies this joint as a one degree of freedom kinematic pair. Prismatic joints provide single-axis sliding often found in hydraulic and pneumatic cylinders.

Ball

In an automobile, ball joints are spherical bearings that connect the control arms to the steering knuckles. They are used on virtually every automobile made and work similarly to the ball-and-socket design of the human hip joint. A ball joint consists of a bearing stud and socket enclosed in a casing; all these parts are made of steel. The bearing stud is tapered and threaded, and fits into a tapered hole in the steering knuckle. A protective encasing prevents dirt from getting into the joint assembly. Usually, this is a rubber-like boot that allows movement and expansion of lubricant. Motion-control ball joints tend to be retained with an internal spring, which helps to prevent vibration problems in the linkage. The "offset" ball joint provides means of movement in systems where thermal expansion and contraction, shock, seismic motion, and torsional motions, and forces are present.

Cotterpin

This is mainly used to connect rigidly two rods which transmit motion in the axial direction, without rotation. These joints may be subjected to tensile or compressive forces along the axes of the rods. The very famous example is the joining of piston rod's extension with the connecting rod in the cross head assembly. Advantages:

Quick assembly and disassembly is possible It can take tensile as well as compressive force. Application:

Joint between piston rod and cross head of a steam engine Joint between valve rod and its steam A steam engine connecting rod strap end Foundation bolt

Bolted A bolted joint is a mechanical joint which is the most popular choice for connecting two members together. It is easy to design and easy to procure parts for, making it a very popular design choice for many applications. Advantage:

Joints are easily assembled/ disassembled by using a torque wrench or other fastener tooling. Clamped members can be axially tensioned at variable preloads. Disadvantage:

Threaded components can fail from fatigue failure. Joints can come loose, requiring re-torqueing. Application:

Pipe flanges Automotive engines Foundation bolts

Screw

Universal

References

Illustrations

Worked examples

Example 1 — a first encounter with Mechanical joint

Start with the simplest possible case. Write down what Mechanical joint claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mechanical joint before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mechanical joint ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mechanical joint

In research: Mechanical joint appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mechanical joint in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mechanical joint is common in secondary-school and first-year university syllabi. It links to neighbouring topics Fasteners, Household hardware, Kinematics, so understanding it makes those chapters shorter.
In everyday life: Look for Mechanical joint outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Mechanical joint in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mechanical joint means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mechanical joint out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mechanical joint in simple terms?

Why does Mechanical joint matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mechanical joint?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mechanical joint.