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| Claimed by Ferguson Beardsley Fall 2017
| | SHREYA LAKSHMISHA SPRING 2026 |
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| ==Main Idea== | | ==Main Idea== |
| | In many real-world situations, analyzing the kinetic energy of an object is more complex than just applying the formula: |
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| In many cases, analyzing the kinetic energy of an object is in fact more difficult than just applying the formula <math> K = \cfrac{1}{2}mv^2 </math>. An example of this is when throwing a basketball because not only does it move through the air but it is also rotating around its own axis. When analyzing more complicated movements like this one, it is necessary to break kinetic energy into different parts, such as rotational, translational, and vibrational, and analyze each one separately.
| | <math> K = \cfrac{1}{2}mv^2 </math> |
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| Translational kinetic energy is the kinetic energy associated with the motion of the center of mass of an object. This would be the basketball traveling in the air from one location to another. While relative kinetic energy is the kinetic energy associated to the rotation or vibration of the atoms of the object around its center or axis. Relative kinetic energy would be the rotation of the basketball around it's axis. Later on this page, we go into more depth about the different types of kinetic energy.
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| Here is a link to a video which explains kinetic energy in detail: [https://youtu.be/Cobhu3lgeMg]
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| ===Kinetic Energy===
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| ==== Total Kinetic Energy ====
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| As we just saw, the total kinetic energy of a multi particle system can be divided into the energy associated with motion of the center of mass and the motion of the center of mass. [http://p3server.pa.msu.edu/coursewiki/doku.php?id=183_notes:energy_sep]
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| <math> K_{total} = K_{translational} + K_{relative} </math>
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| The relative kinetic energy is composed of motion due to rotation about the center of mass and vibrations/oscillations of the object. [http://p3server.pa.msu.edu/coursewiki/doku.php?id=183_notes:energy_sep]
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| <math> K_{total} = K_{translational} + K_{rotational} + K_{vibrational} </math>
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| ====Calculating Translational Kinetic Energy====
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| "Translation" means to move from one location to another location. By calculating translational kinetic energy, we can track how one object moves from one location to another. Since the translational kinetic energy is associated to the movement of the center of mass of the object, it is important to know how to calculate the location of the center of mass and the velocity of the center of mass which is shown in the two equations below:
| | For example when a basketball is thrown, it is not only moving through space, but also rotating about its own axis. Because of this, the total kinetic energy must be broken into components. |
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| <math> r_{CM} = \cfrac{m_1r_1 + m_2r_2+m_3r_3 + ...}{m_1 + m_2 +m_3} </math>
| | The total kinetic energy of a system can be separated into: |
| <math> v_{CM} = \cfrac{m_1v_1 + m_2v_2+m_3v_3 + ...}{m_1+ m_2 +m_3} </math>[http://p3server.pa.msu.edu/coursewiki/doku.php?id=183_notes:center_of_mass]
| | * Translational energy (motion of the center of mass) |
| | * Rotational energy (spinning motion) |
| | * Vibrational energy (internal motion of particles) |
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| Here is a link to video if you want to refresh knowledge one center of mass: [https://youtu.be/5qwW8WI1gkw]
| | This breakdown allows us to more accurately analyze motion in physical systems. |
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| The motion of canter of mass is described by the velocity of center of mass. Using the total mass and the velocity of the center of mass, we :
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| <math> K_{translational} = \cfrac{1}{2}M_{total}v_{CM}^2 </math>[http://p3server.pa.msu.edu/coursewiki/doku.php?id=183_notes:energy_sep]
| | [[File:Rolling Racers - Moment of inertia.gif|Rolling_Racers_-_Moment_of_inertia]] |
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| ====Calculating Vibrational Kinetic Energy==== | | ===Mathematical Model=== |
| | === Total Kinetic Energy === |
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| The total energy due to vibrations is the sum of the potential energy associated with interaction causing the vibrations and the kinetic energy of the vibrations.
| | <math>K_{total} = K_{translational} + K_{rotational} + K_{vibrational}</math> |
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| <math> E_{vibrational} = K_{vibrational} +U_{s} </math>
| | This equation shows that energy must be considered in multiple forms when objects both move and rotate. |
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| The easiest way to find vibrational kinetic energy is by knowing the other energy terms and isolating the vibrational kinetic energy. This is when there is no rotational kinetic energy:
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| <math> E_{total} = K_{trans} + K_{vibrational} + U_{s} +E_{rest}</math>
| | ====Translational Kinetic Energy==== |
| <math> K_{vibrational} = E_{total} - (K_{trans} + U_{s} +E_{rest})</math>
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| ====Calculating Rotational Kinetic Energy==== | | ::<math>K_{trans} = \cfrac{1}{2}Mv_{CM}^2</math> |
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| Rotational kinetic energy is the energy due to the rotation about center of mass and can be calculated by finding the angular momentum and inertia, which be discussed in greater detail in the next two sections. The equation used to find kinetic rotational energy is below:
| | * <math>M</math>: total mass |
| | * <math>v_{CM}</math>: velocity of the center of mass |
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| <math> K_{rotational} =1/2I_{cm}{w}^2</math>
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| Here are links to two videos that cover rotational kinetic energy and moment of interim: [https://youtu.be/craljBk-E5g][https://youtu.be/XlFlZHfAZeE]
| | The center of mass is calculated as: |
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| =====Calculating Moment of Inertia===== | | ::<math>r_{CM} = \cfrac{\sum m_ir_i}{\sum m_i}</math> |
| | ::<math>v_{CM} = \cfrac{\sum m_iv_i}{\sum m_i}</math> |
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| The moment of inertia of an object shows the difficulty of rotating an object, since the larger moment of inter the more energy required to rotate the object at the same angular velocity as an object with smaller moment of inertia. It is the sum of the products of the mass of each particle in the object with the square of their distance from the axis of rotation. The general formula for calculating the moment of inertia of an object is:
| | '''Key Idea:''' Translational energy depends only on how the object moves. |
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| <math> I = m_1r_{\perp,1}^2 + m_2r_2{\perp,2}^2 + m_3r_{\perp,3}^2 +...</math>
| | [[File:Beam with pivot P, center of mass S and center of percussion C.svg|Beam_with_pivot_P,_center_of_mass_S_and_center_of_percussion_C]] |
| Units: <math> kg.m^2 </math>
| | --- |
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| Here <math> r_1, r_2, r_3 </math> represent the perpendicular distance from the point/axis of rotation.
| | ====Rotational Kinetic Energy==== |
| | The total energy due to vibrations is the sum of the potential energy associated with interactions causing the vibrations and the kinetic energy of the vibrations. |
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| Moment of Inertia is actually calculated using Calculus. These values we obtain for standard objects are not once you will need to derive, but conceptually understanding how they come to be will help you understand Moment of Inertia and it's impact on a solid. Below are a few moment of inertia used most frequently
| | ::<math>K_{rot} = \cfrac{1}{2}I\omega^2</math> |
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| [[File :https://cnx.org/resources/4c906c92cebe30d9486deb2a682acf561d23c9c1]]
| | * <math>I</math>: moment of inertia |
| | * <math>\omega</math>: angular velocity |
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| When you compare two bodies rotating with the same kinetic energy and one of them has a higher moment of Inertia, then the one with the higher moment of Inertia has a lower speed. If angular speed is lower and radius is larger that means mass must be small since Moment of Inertia also depends on mass and distance from axis of rotation. So we can deduce such relations which helps us understand how the moment of Inertia of an object actually affects the object in different ways.
| | ====Moment of Inertia==== |
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| ===== Angular Speed ===== | | ::<math>I = \sum m_i r_i^2</math> |
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| The angular speed is that rate at which the object is rotating. It is given in the following formula:
| | This measures how difficult it is to rotate an object. |
| <math> \omega = \cfrac{2\pi}{T} </math>
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| The angle which the disk turns is 2 pi in a time T. It is measured in units in radians per second. The tangential velocity of an object is related to some distance r and at the angular speed because the tangential velocity increases when the distance from the center of an object increases. It is shown in the equation below:
| | '''Important Insight:''' |
| <math> v(r)=wr</math>
| | Mass farther from the axis increases rotational energy because of the \(r^2\) term. |
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| [[File:Users/fergie/Desktop/angularvelocity.pngample.jpg]]
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| ==== Point Particle System VS Extended System ====
| | [[File:Moment of inertia solid sphere.svg|Moment_of_inertia_solid_sphere]] |
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| When calculating the total energy of a system, it will sometimes contain one or more types of kinetic energies.
| | --- |
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| Let's think about a system modeled as a point particle system. In this model of a system, we think of the object as one point, located at its center of mass. It becomes clear that there can only be translational kinetic energy since there cannot be any rotational kinetic energy. This is because there are no atoms rotating about the center of mass, since we are thinking of the center of mass as the entire object. All the forces act on the center of mass.
| | =====Angular Speed and Velocity===== |
| [[File:Example.jpg]]
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| <math> \triangle E_{system} = W </math>
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| <math> W = F_{net} . \triangle r_{CM} </math>
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| <math> \triangle E_{system} = \triangle K_{translational} </math>
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| <math> \triangle K_{translational} = F_{net} . \triangle r_{CM} </math>
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| Viewing a system as a point particle system allows us to easily calculate the translational kinetic energy. This translational kinetic energy will be the same in the extended system as it is in the point particle system. We can use this value to calculate other terms in the general equation in the extended system. In the extended system we add up all the forces that might have different points of application. In the extended system, all the atoms, their rotation about the axis, and the general movement of the center of mass is considered in the extended/real system.
| | ::<math>\omega = \cfrac{2\pi}{T}</math> |
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| We start with the general energy equation:
| | ::<math>v = \omega r</math> |
| <math> \triangle E_{system} = W </math> | |
| <math> W = F_1r_1 + F_2r_2 + F_3r_3 +... +F_nr_n </math>
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| <math> \triangle K_{translational} + \triangle K_{rotational} + \triangle K_{vibrational} = W
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| Note: There may be spring potential energy and rest energy included for both point particle and real system depending on the example.
| | Points farther from the center move faster. |
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| Here are some videos that go into more depth about point particle vs real system:
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| [[File:https://youtu.be/vL5yTCyRMGk]]
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| ===A Computational Model=== | | =====Vibrational Kinetic Energy===== |
| ==== Vpython ==== | |
| There are not many applications of vpython for this chapter because it necessitates such a conceptual way of thinking. However, it is possible to make a program that calculates the rotational energy given displacements for each force and the magnitude of the force. The mass of the object and the initial conditions would have to be given as well.
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| ====Visualizing translational and rotational kinetic energy ====
| | Vibrational energy comes from internal motion of particles within an object. |
| It is important to really think about translational kinetic energy as the movement of the center of mass and only that. In the point particle system, only translational kinetic energy is present because we are visualizing the object only as its center of mass, and that is therefore the only kind of movement we have. Let's take the earth as an example. The earth rotates around itself, as well as around the sun. If you think of the earth only in terms of its center of mass, you realize that the center of mass only has one kind of movement: around the sun. It is useful to think of the earth in this case, the point particle system, as a dot, located at its center of mass.
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| [[File:Wiki 5.gif|center]]
| | * Important in molecules and thermal systems |
| | * Usually not directly calculated in introductory physics problems |
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| In the extended system, however, we consider the movement of the center of mass as well as the movement of all the atoms around it. Since the atoms of the earth that are not its center rotate (one rotation every 24h), there is rotational energy. Its center of mass is still moving around the sun, there is therefore also translational energy. Here, we think of the earth as a sphere, not a dot, in which the atoms rotate about an axis or center.
| | --- |
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| [[File:Wiki 7.jpeg|center]]
| | ===Physical Intuition=== |
| | Consider a rolling wheel: |
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| For another visual approach of this concept, you can watch the following video: https://www.youtube.com/watch?v=zDcf7eEaP0M.
| | * Moves forward -> translational energy |
| | * Spins -> rotational energy |
| | * Internal atoms vibrate -> vibrational energy |
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| ==Examples== | | ==Examples== |
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| ===Simple=== | | ===Conceptual Example=== |
| ''Problem statement'':
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| Calculate the rotational kinetic energy of a wheel of radius 100cm, mass 10kg, with and angular velocity of 22 radians/s.
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| ''Solution'':
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| We know how to calculate the moment of inertia for a disk, and the moment of inertia for a wheel will be the same since all the atoms are at the same distance from the center. Therefore, <math> I = MR^2 = (10)(1)^2 = 10 kgm^2 </math>
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| From there, we can easily calculate the rotational kinetic energy:
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| <math> K_{rotational} = \cfrac{1}{2}I\omega^2 = \cfrac{1}{2}(10)(22)^2 = 2420 </math> Joules
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| ===Middling===
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| ''Problem statement'':
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| A string is wrapped around a disk of radius 0.15m and mass 3kg. The disk is initially at rest, but you pull the string with a force of 10N along a smooth surface. The disk moves a distance d = 0.1m and your hand pulls through a distance h = 0.2m. What is the speed of the center of mass of the disk after having pulled the string?
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| [[File:Wiki 2.png|center]]
| | A bowling ball rolls without slipping. |
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| ''Solution'': | | '''Which energies are present?''' |
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| The problem states that the disk is moving on a smooth surface, so there is no friction here. Since the problem asks about the speed of the center of mass, we will consider the point particle system first. We start with:
| | * Translational ✔ |
| | * Rotational ✔ |
| | * Vibrational ✖ (ignored at this level) |
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| <math> \triangle K_{translational} = F_{net} . \triangle r_{CM} </math>
| | --- |
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| We know that the translational kinetic energy is <math> K = \cfrac{1}{2}mv_{CM}^2 </math>
| | ===Calculation Example=== |
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| So we end up with:
| | A solid disk rolls without slipping. |
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| <math> \cfrac{1}{2}mv_{CM,f}^2 - \cfrac{1}{2}mv_{CM,i}^2 = F_{net} . \triangle r_{CM} </math> | | Given: |
| | * <math>m = 2 \, kg</math> |
| | * <math>v = 3 \, \frac{m}{s}</math> |
| | * <math>I = \cfrac{1}{2}mr^2</math> |
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| Because initially the disk is still, we can reduce this equation to:
| | Step 1: Translational Energy |
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| <math> \cfrac{1}{2}mv_{CM,f}^2 = F_{net} . \triangle r_{CM} </math> | | ::<math>K_{trans} = \cfrac{1}{2}mv^2 = 9 \, J</math> |
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| <math> v_{CM,f}^2 = \cfrac{2. F_{net} . \triangle r_{CM}}{m} </math>
| | Step 2: Rotational Energy |
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| <math> v_{CM,f} = \sqrt{\cfrac{2. F_{net} . \triangle r_{CM}}{m}} </math> | | ::<math>K_{trans} = \cfrac{1}{2}mv^2 = 9 \, J</math> |
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| <math> v_{CM,f} = \sqrt{\cfrac{ (2)(10)(0.1)}{3}} </math> | | Using <math>\omega = \cfrac{v}{r}</math>: |
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| <math> v_{CM,f} = 0.816 </math> m/s | | ::<math>K_{rot} = \cfrac{1}{4}mv^2 = 4.5 \, J</math> |
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| ===Difficult===
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| ''Problem statement''
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| A box contains a machinery that can rotate. The mass of the box and what it contains is 10kg. A string is wound around the machinery inside the box and comes out of a hole at the top of the box. Before you pull the string, the machinery is not rotating and the box is sitting still. You then pull 0.9m of string out of the box with a force F = 100N and the box lifts up a distance of 0.2m. What is the rotational Kinetic energy of the mechanism inside the box?
| | Total Energy: |
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| [[File:wiki 6.png|center]]
| | ::<math>K_{total} = 13.5 \, J</math> |
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| ''Solution''
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| We cannot calculate the rotational energy directly because we do not have any indication of the shape of the mechanism and its angular speed. Therefore, we will use the point particle system and the extended system to find this value. Begin by finding the value of the translational kinetic energy of the system by using the point particle model.
| | ===Common Mistakes=== |
| We have:
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| <math> \triangle K_{translational} = F_{net} . \triangle r_{CM} </math>
| | * Forgetting rotational energy in rolling problems |
| <math> K_{translational,f} - K_{translational,i} = F_{net} . \triangle r_{CM} </math>
| | * Using incorrect relationship between \(v\) and \(\omega\) |
| | * Ignoring moment of inertia differences |
| | * Assuming only translational motion matters |
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| The initial translational kinetic energy is 0 because the center of mass of the object is not moving initially.
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| <math> K_{translational,f} = F_{net} . \triangle r_{CM} </math>
| | ==Computational Model== |
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| <math> K_{translational,f} = (F_{hand} - F_{grav}) (0.2) </math>
| | GlowScript simulation: |
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| <math> K_{translational,f} = (114 - mg) (0.2) </math>
| | https://trinket.io/glowscript/31d0f9ad9e |
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| <math> K_{translational,f} = (114 - (10)(9.8)) (0.2) </math>
| | This model helps visualize rotational motion and energy changes. |
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| <math> K_{translational,f} = 3.2 </math> Joules
| | --- |
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| Now let's look at the extended system:
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| Here, we have:
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| <math> \triangle K_{translational} + \triangle K_{rotational} = F_{net} . displacement </math>
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| Since there is no initial translational or rotational kinetic energy, we get:
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| <math> K_{translational,f} + K_{rotational,f} = F_{net} . displacement </math>
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| <math> K_{rotational,f} = F_{net} . displacement - K_{translational} </math>
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| The gravitational force mg acts through the distance that the center of mass of the box moves, while the force of your hand acts through that distance plus the distance the string uncoils. Therefore, we have:
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| <math> K_{rotational,f} = (114)(0.2 + 0.9) - (10)(9.8)(0.2) - 3.2 </math>
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| <math> K_{rotational,f} = 102.6 </math> Joules
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| ==Connectedness== | | ==Connectedness== |
| #How is this topic connected to something that you are interested in?
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| In the book, this topic is very much related to sports. It uses countless examples from diving, ice skating or frisbee to demonstrate why kinetic energy can be separated into two terms. I have always been interested in sports and they were always a big part of my life. Therefore when I read the book, this was one of the most interesting sections to me because I felt some kind of connection to it, like it applied to my life, since I had ice-skated and dove when I was young.
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| ##How is it connected to your major?
| | '''Personal Connection:''' |
| Some biomedical engineers go on to work with sports stars on smart clothes or even prosthetics, in which case they have to deal with rotation and vibration, in addition to regular kinetic energy. The study of biomechanics largely relies on physics as well.
| | Dance and sports like tennis involve rotation and motion, similar to energy concepts discussed here. |
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| ###Is there an interesting industrial application?
| | '''Academic Connection:''' |
| There are many developments of machines that will use kinetic energy for power. We may very well see a few years from now a shoe on the market that powers your cell phone or any other type of technology. There are many possibilities for advancements such as this one.
| | Important in physics, engineering, and chemistry for analyzing motion and energy systems. |
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| ==History==
| | '''Industrial Applications:''' |
| | * Flywheels for energy storage |
| | * Rotating machinery |
| | * Engines and turbines |
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| Kinetic energy was first set apart from potential energy by Aristotle. However, it wasn't until 1929 that Gaspard-Gustave Coriolis showed the first signs of understanding of kinetic energy the way that we do today. The term was later coined by William Thomson.
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| == See also == | | ===History=== |
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| For more specific information on point particle systems and extended systems:
| | The concept of kinetic energy developed over time through contributions from scientists such as Aristotle, Leibniz, Bernoulli, and Gaspard-Gustave Coriolis. The term “kinetic energy” was later coined by Lord Kelvin. |
| http://www.physicsbook.gatech.edu/Point_Particle_Systems ;
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| http://www.physicsbook.gatech.edu/Real_Systems
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| For more specific information on the conservation of energy:
| | ===Why This Matters for Exams=== |
| http://www.physicsbook.gatech.edu/Conservation_of_Energy
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| For more information on potential energy and when it is present:
| | Most physics problems: |
| http://www.physicsbook.gatech.edu/Potential_Energy
| | * Combine translation and rotation |
| | * Require identifying ALL forms of energy |
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| For information on how to take this concept further to calculate thermal energy in some instances:
| | Missing one energy component often leads to incorrect answers. |
| http://www.physicsbook.gatech.edu/Thermal_Energy
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| ===Further reading===
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| Matter and Interactions By Ruth W. Chabay, Bruce A. Sherwood - Chapter 9
| | ===Summary=== |
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| http://www.scienceclarified.com/everyday/Real-Life-Physics-Vol-2/Energy-Real-life-applications.html
| | Kinetic energy in real systems consists of multiple components. By separating it into translational, rotational, and vibrational parts, we can more accurately understand and analyze motion. |
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| http://spie.org/x48868.xml
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| ===External links===
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| http://hyperphysics.phy-astr.gsu.edu/hbase/rke.html
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| http://www.sparknotes.com/physics/rotationalmotion/rotationaldynamics/section3.rhtml
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| http://hyperphysics.phy-astr.gsu.edu/hbase/rotwe.html
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| http://classroom.synonym.com/kinetic-energy-potential-energy-apply-everyday-life-15430.html
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| ==References== | | ==References== |
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| All images used on this page do not belong to me.
| | *https://openstax.org/details/books/university-physics-volume-1 |
| All problem examples are from the Matter and Interactions Physics book referenced below.
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| https://en.wikipedia.org/wiki/Kinetic_energy#History_and_etymology | |
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| http://www.murderati.com/category/stephen-jay-schwartz/
| | *https://www.khanacademy.org/science/physics/work-and-energy |
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| http://learning.alfriston.bucks.sch.uk/course/view.php?id=47
| | *https://en.wikipedia.org/wiki/Kinetic_energy |
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| http://www.school-for-champions.com/astronomy/earth_motion.htm#.Vloe4HarSM8
| | *https://en.wikipedia.org/wiki/Moment_of_inertia |
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| Matter and Interactions By Ruth W. Chabay, Bruce A. Sherwood - Chapter 9
| | *https://trinket.io/glowscript/ |
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| [[Category:Energy]]
| | *https://ocw.mit.edu/courses/physics/ |
SHREYA LAKSHMISHA SPRING 2026
Main Idea
In many real-world situations, analyzing the kinetic energy of an object is more complex than just applying the formula:
[math]\displaystyle{ K = \cfrac{1}{2}mv^2 }[/math]
For example when a basketball is thrown, it is not only moving through space, but also rotating about its own axis. Because of this, the total kinetic energy must be broken into components.
The total kinetic energy of a system can be separated into:
- Translational energy (motion of the center of mass)
- Rotational energy (spinning motion)
- Vibrational energy (internal motion of particles)
This breakdown allows us to more accurately analyze motion in physical systems.
Mathematical Model
Total Kinetic Energy
[math]\displaystyle{ K_{total} = K_{translational} + K_{rotational} + K_{vibrational} }[/math]
This equation shows that energy must be considered in multiple forms when objects both move and rotate.
Translational Kinetic Energy
- [math]\displaystyle{ K_{trans} = \cfrac{1}{2}Mv_{CM}^2 }[/math]
- [math]\displaystyle{ M }[/math]: total mass
- [math]\displaystyle{ v_{CM} }[/math]: velocity of the center of mass
The center of mass is calculated as:
- [math]\displaystyle{ r_{CM} = \cfrac{\sum m_ir_i}{\sum m_i} }[/math]
- [math]\displaystyle{ v_{CM} = \cfrac{\sum m_iv_i}{\sum m_i} }[/math]
Key Idea: Translational energy depends only on how the object moves.
Beam_with_pivot_P,_center_of_mass_S_and_center_of_percussion_C
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Rotational Kinetic Energy
The total energy due to vibrations is the sum of the potential energy associated with interactions causing the vibrations and the kinetic energy of the vibrations.
- [math]\displaystyle{ K_{rot} = \cfrac{1}{2}I\omega^2 }[/math]
- [math]\displaystyle{ I }[/math]: moment of inertia
- [math]\displaystyle{ \omega }[/math]: angular velocity
Moment of Inertia
- [math]\displaystyle{ I = \sum m_i r_i^2 }[/math]
This measures how difficult it is to rotate an object.
Important Insight:
Mass farther from the axis increases rotational energy because of the \(r^2\) term.
Moment_of_inertia_solid_sphere
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Angular Speed and Velocity
- [math]\displaystyle{ \omega = \cfrac{2\pi}{T} }[/math]
- [math]\displaystyle{ v = \omega r }[/math]
Points farther from the center move faster.
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Vibrational Kinetic Energy
Vibrational energy comes from internal motion of particles within an object.
- Important in molecules and thermal systems
- Usually not directly calculated in introductory physics problems
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Physical Intuition
Consider a rolling wheel:
- Moves forward -> translational energy
- Spins -> rotational energy
- Internal atoms vibrate -> vibrational energy
Examples
Conceptual Example
A bowling ball rolls without slipping.
Which energies are present?
- Translational ✔
- Rotational ✔
- Vibrational ✖ (ignored at this level)
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Calculation Example
A solid disk rolls without slipping.
Given:
- [math]\displaystyle{ m = 2 \, kg }[/math]
- [math]\displaystyle{ v = 3 \, \frac{m}{s} }[/math]
- [math]\displaystyle{ I = \cfrac{1}{2}mr^2 }[/math]
Step 1: Translational Energy
- [math]\displaystyle{ K_{trans} = \cfrac{1}{2}mv^2 = 9 \, J }[/math]
Step 2: Rotational Energy
- [math]\displaystyle{ K_{trans} = \cfrac{1}{2}mv^2 = 9 \, J }[/math]
Using [math]\displaystyle{ \omega = \cfrac{v}{r} }[/math]:
- [math]\displaystyle{ K_{rot} = \cfrac{1}{4}mv^2 = 4.5 \, J }[/math]
Total Energy:
- [math]\displaystyle{ K_{total} = 13.5 \, J }[/math]
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Common Mistakes
- Forgetting rotational energy in rolling problems
- Using incorrect relationship between \(v\) and \(\omega\)
- Ignoring moment of inertia differences
- Assuming only translational motion matters
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Computational Model
GlowScript simulation:
https://trinket.io/glowscript/31d0f9ad9e
This model helps visualize rotational motion and energy changes.
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Connectedness
Personal Connection:
Dance and sports like tennis involve rotation and motion, similar to energy concepts discussed here.
Academic Connection:
Important in physics, engineering, and chemistry for analyzing motion and energy systems.
Industrial Applications:
- Flywheels for energy storage
- Rotating machinery
- Engines and turbines
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History
The concept of kinetic energy developed over time through contributions from scientists such as Aristotle, Leibniz, Bernoulli, and Gaspard-Gustave Coriolis. The term “kinetic energy” was later coined by Lord Kelvin.
Why This Matters for Exams
Most physics problems:
- Combine translation and rotation
- Require identifying ALL forms of energy
Missing one energy component often leads to incorrect answers.
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Summary
Kinetic energy in real systems consists of multiple components. By separating it into translational, rotational, and vibrational parts, we can more accurately understand and analyze motion.
References