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A rigid body (also known as a rigid object) is a solid body with no or minimal deformation that may be ignored. Regardless of external forces or moments acting on a rigid body, the distance between any two given points remains constant over time. A rigid body is typically thought of as a continuous mass distribution. A rigid body does not exist under special relativity, and objects can only be assumed to be rigid if they are not traveling near the speed of light. Molecules, for example, are commonly seen as rigid bodies since they are made up of point masses such as electrons and nuclei.
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Key Takeaways: Equilibrium, Torque, Force, Elastic collision, Tension, Center of gravity
Rigid Body
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The term "rigid body" refers to a body that has little or no deformation. A rigid body is typically thought of as a continuous mass distribution. When all of the bodies are made up of atoms and molecules in a condition of uniform motion, it is called a perfectly rigid body. All microscopic displacements are minimal and minor, and the given body is referred to as stiff in this scenario.
Examples of Rigid Bodies
A ball bearing composed of hardened steel is a good example of a Rigid Body in real-time. Try dropping a ball bearing on a polished marble floor; it'll bounce nearly as effectively as a Superball. It's because it possesses near-perfect flexibility while being a Rigid Body. Quantum fields, which are electromagnetic forces between atoms, exist in all bodies, no matter how stiff they are. So, when someone taps a really hard object, nearly no mechanical energy is wasted since it behaves like a perfect spring, albeit one that is incredibly hard. It will also expand slightly if heated.
The flutter of an airplane wing during a flight, for example, is small in comparison to the motion of the aircraft as a whole. These deformations, on the other hand, become of vital importance if one is interested in stresses created in the wing as a result of flutter.
Rigid Body Dynamic
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Though this is not true because all bodies distort in some way during movement. Still, in rigid bodies, this deformation is small, therefore it is assumed that it does not exist. A rigid body can move in a variety of ways, and the translational and rotational motions of a rigid body are discussed in this article.
Translatory Motion
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Translational Motion is defined as the motion that allows a body to travel from one point in space to another. The motion of a bullet discharged from a gun is an example of a Translatory motion. The rectilinear motion is defined as a body movement that follows a straight line. A position occupied by the body at any moment is depicted in the diagram below. The object's position is defined by the distance x, which is denoted by an appropriate sign. When the position of an object at a specific time is known, the motion of the object can be calculated. This is expressed as an equation that connects the distance x to the time t. For instance, consider x = 6t-4 or a graph.
The motion of an item in two or three dimensions is difficult. Two coordinates are required to fix the object's position in two dimensions.
Translational Motion Examples
Translational Motion examples, as well as a simple projectile motion example: a ball rolling off a table, are shown in the diagram below. The horizontal direction will be defined by the x-axis, while the vertical direction will be determined by the y-axis. Using a 10 m/s beginning velocity for the ball rolling on a flat table.
Translation Motion
The initial x-element of velocity (v0x) is 10 m/s (constant) when the ball is on the table, the initial y-element of velocity is 0 m/s, the x-component of acceleration is 0 m/s², and the y-component of acceleration is 0 m/s². The sections of the velocity/acceleration that indicate the places in the x/y-direction are called elements of velocity and acceleration.
Some other examples of Translational Motion are:
- Moving the Bus
- Sailing of Boat
- Dog Walking of Dog
- A plant is shaken by a person
- A stone falling straight at the surface of the earth
- A coin moving over a carrom board
Rotational Motion
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A common type of circular motion is rotational motion. Kinematics may be investigated, and relationships between position, acceleration, and velocity can be learned, just like projectile motion. Unless an external force acts on an object in motion, Newton's first law states that it will remain in motion at a constant velocity. There will be a change in the direction of the velocity if the force exerted is perpendicular to the direction of motion. If a force acts perpendicular to the moving object, the object will travel at a constant speed in a circular route; this is known as uniform circular motion.
Only rigid bodies are dealt with in rotational motion physics. The Rigid Body is a body that preserves its general shape, implying that the particles that make up the body remain in a comparable position relative to one another.
Rotational Motion
Rotational Motion Examples
The wheel or rotor of a motor, which appears in rotation motion problems, is a common example of the rotational motion of a rigid body.
Other examples:
- Moving by Bus
- Sailing of Boat
- Dog walking
- A person shaking the plant.
- A stone falls straight at the surface of the earth.
- Movement of a coin over a carrom board
Properties of Rigid Body Motion
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Two features of rigid body motion considerably simplify kinematics. To do so, an arbitrary Rigid Body motion is seen to fall into one of three categories: Translational Motion, Rotational Motion, or General Plane Motion.
Curvilinear, rectilinear, and translation: The form of motion in which every line in the body remains parallel to its initial place is known as translational motion. The motion of the body is completely characterized by the motion of any point in the body in Translational Motion, and all points of the body have the same velocity and acceleration.
Things to Remember
- On a rigid body, all lines have the same angular velocity and angular acceleration.
- The translation of an arbitrary point, followed by a rotation around the point, can be decomposed into rigid motion.
- In translational motion, the body has displacement in equal intervals of time
- In rotational motion the body travels the same angular displacement in an equal interval of time.
- If the distance between any two locations in a rigid body is always constant, it is considered rigid. In actuality, nobody is completely rigid.
- The form of motion in which every line in the body remains parallel to its original position is known as translational motion.
- Any plane motion that is neither a pure rotation nor a translation is classified as general plane motion. A generic plane motion, on the other hand, may always be reduced to the sum of translation and rotation.
Sample Questions
Ques. What is mixed motion? Give an example. (2 marks)
Ans. Mixed motion occurs when a body performs both translational and rotational motions at the same time. Rotational motion, for example, is when a wheel revolves on its axis at its center. When it moves (translates) along the road while moving on its axis, it exhibits mixed motion.
Ques. Is Vibratory Motion an Example of Translatory Motion? (3 marks)
Ans. The particles of matter vibrate in all phases of matter, including liquid, solid, and gas. There are also rotational and translatory motions in liquids and gasses. Only vibratory motion occurs in solids, which is caused by the vibration of the two molecules. Because the distance between the molecules of a solid is so small, vibration transmission is quick and efficient. So the Vibratory motion is also a type of translatory motion because the moment is in a straight line.
Because translatory motion is not conceivable in solids, the question of why we can't use them in pistons, as opposed to gasses and liquids, may be answered. You might not think that translator motion is possible when looking at solids like the spring, but it is because of the vibration and flexibility. Because of its flexibility, it is very easy for vibration to arise. The solid is mobilized as the vibration spreads.
Ques. What is the difference between Translational Motion and Rotational Motion? (2 marks)
Ans. The main distinction between Translational Motion and Rotational Motion is that Translational Motion involves the sliding of an object in one or more of the three dimensions x, y, or z, whereas Rotational Motion involves the continuous rotation of an object around an internal axis. Translational motion occurs when every line in the body remains parallel to its initial position, whereas rotational motion occurs when the body rotates around a fixed axis.
Ques. What are examples of Translational Motion and Rotational Motion? (2 marks)
Ans. Moving a bus, sailing a boat, walking a dog are all examples of translational motions. When a human shakes a plant, it causes it to shake. A coin moving across a carrom board, a stone falling straight at the earth's surface. Bus travel, boat sailing, dog walking, a person shaking a plant, a stone falling straight to the earth's surface, and the movement of a coin across a carrom board are all examples of rotational motions.
Ques. Does a rigid body conserve its shape during motion? (2 marks)
Ans. A rigid body is a particle system like this. The separation between the constituent particles of a rigid body does not vary as it moves. The shape of a rigid body is kept during motion, according to this definition. A rigid body (also known as a rigid object) is a solid body with no or minimal deformation that can be ignored in physics. Regardless of external forces or moments acting on a rigid body, the distance between any two given points remains constant over time.
Ques. What is Rectilinear translational Motion? (2 marks)
Ans. It is considered to be in rectilinear motion when an object in translatory motion moves in a straight line. When the body moves in a straight line, rectilinear motion is the most common type of translational motion. An automobile traveling in a straight path and a bullet being fired are both examples of rectilinear motion.
Ques. Does a rigid body conserve its shape during motion? (2 marks)
Ans. The shape of a rigid body is kept during motion, according to this definition. A rigid body, like a point mass, is an idealization because, when enormous forces are applied, the distances between particles alter, sometimes infinitesimally. As a result, there is nothing in nature that compares to a fully rigid body. On a rigid body, all lines have the same angular velocity and angular acceleration. The translation of an arbitrary point, followed by a rotation around the point, can be decomposed into rigid motion.
Ques. Do rigid bodies deform? (2 marks)
Ans. When subjected to loads, rigid bodies do not deform (stretch, compress, or bend), whereas deformable bodies do. Although no physical body is rigid, most bodies deform so little that it has a negligible impact on the analysis. External loads, intrinsic activity (e.g. muscular contraction), body forces (such as gravity or electromagnetic forces), or changes in temperature, moisture content, or chemical reactions, among other things, can cause deformation.
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