Period and Frequency

The duration is the duration of one bicycle in a repeating event, when the frequency is the variety of cycles every unit time.

You are watching: Increasing the mass attached to a spring will increase the period of its vibrations.

Key Takeaways

Key PointsMotion the repeats itself regularly is referred to as periodic motion. One complete repetition the the motion is dubbed a cycle. The duration of every cycle is the period.The frequency describes the number of cycles perfect in one interval of time. It is the mutual of the duration and have the right to be calculated through the equation f=1/T.Some motion is finest characterized by the angular frequency (ω). The angular frequency refers to the angular displacement every unit time and also is calculated from the frequency through the equation ω=2πf.Key Termsperiod: The expression of one bike in a repeating event.angular frequency: The angular displacement per unit time.frequency: The quotient that the variety of times n a periodic phenomenon wake up over the moment t in which it occurs: f = n / t.

Period and also Frequency

The usual physics terminology for movement that repeats itself over and over is periodic motion, and also the time forced for one repeat is dubbed the period, regularly expressed together the letter T. (The prize P is no used since of the feasible confusion with momentum. ) One finish repetition that the activity is referred to as a cycle. The frequency is defined as the variety of cycles per unit time. Frequency is usually denoted by a Latin letter f or by a Greek letter ν (nu). Note that period and frequency room reciprocals of each other.


Sinusoidal waves of varying Frequencies: Sinusoidal tide of various frequencies; the bottom tide have greater frequencies than those above. The horizontal axis represents time.

\textf = 1/\textT

For example, if a newborn baby’s love beats at a frequency of 120 time a minute, its duration (the interval in between beats) is fifty percent a second. If you calibrate your intuition so that you mean large frequencies to be paired with brief periods, and vice versa, you may avoid part embarrassing failure on physics exams.


Locomotive Wheels: The locomotive’s wheel spin at a frequency the f cycles per second, i m sorry can also be described as ω radians per second. The mechanically linkages enable the straight vibration the the steam engine’s pistons, at frequency f, to journey the wheels.

In SI units, the unit that frequency is the hertz (Hz), called after the German physicist Heinrich Hertz: 1 Hz indicates that an occasion repeats when per second. A classic unit that measure used with rotating mechanical devices is revolutions per minute, abbreviation RPM. 60 RPM equals one hertz (i.e., one revolution per second, or a period of one second). The SI unit for period is the second.

Angular Frequency

Often periodic activity is best expressed in regards to angular frequency, represented by the Greek letter ω (omega). Angular frequency refers to the angular displacement every unit time (e.g., in rotation) or the price of readjust of the step of a sinusoidal waveform (e.g., in oscillations and also waves), or as the price of adjust of the dispute of the sine function.

\texty(\textt) = \textsin(\theta (\textt))=\textsin(\omega \textt)=\textsin(2\pi \textft)

\omega =2\pi \textf

Angular frequency is regularly represented in units of radians per second (recall there room 2π radians in a circle).

Period the a massive on a Spring

The period of a mass m ~ above a spring of spring continuous k have the right to be calculated together \textT=2\pi \sqrt\frac\textm\textk.

Learning Objectives

Identify parameters important to calculate the duration and frequency of an oscillating fixed on the end of suitable spring

Key Takeaways

Key PointsIf an object is vibrating come the right and left, climate it must have actually a leftward pressure on it when it is top top the ideal side, and a rightward pressure when that is ~ above the left side.The restoring force reasons an oscillating object to move earlier toward its secure equilibrium position, where the net pressure on that is zero.The easiest oscillations take place when the restoring force is directly proportional come displacement. In this instance the pressure can be calculated together F=-kx, whereby F is the restoring force, k is the pressure constant, and also x is the displacement.The movement of a fixed on a spring deserve to be described as Simple Harmonic Motion (SHM): oscillatory motion that adheres to Hooke’s Law.The duration of a fixed on a spring is given by the equation \textT=2\pi \sqrt\frac\textm\textkKey TermsRestoring force: A variable force that offers rise to an equilibrium in a physics system. If the system is perturbed away from the equilibrium, the restoring pressure will often tend to bring the system back toward equilibrium. The restoring pressure is a function only of place of the fixed or particle. The is constantly directed earlier toward the equilibrium position of the systemamplitude: The maximum absolute worth of some amount that varies.

Understanding the Restoring Force

Newton’s first law indicates that an object oscillating earlier and forth is experiencing forces. Without force, the thing would relocate in a directly line at a constant speed fairly than oscillate. That is essential to understand just how the pressure on the object depends on the object’s position. If an item is vibrating to the right and also left, then it must have actually a leftward pressure on it as soon as it is ~ above the appropriate side, and a rightward pressure when the is ~ above the left side. In one dimension, we have the right to represent the direction of the force using a confident or an unfavorable sign, and also since the force transforms from optimistic to an adverse there should be a allude in the center where the pressure is zero. This is the equilibrium point, where the object would stay at remainder if it was released at rest. That is common convention to specify the origin of ours coordinate system so that x equates to zero in ~ equilibrium.

Oscillating Ruler: when displaced from its upright equilibrium position, this plastic ruler oscillates ago and forth because of the restoring force opposing displacement. Once the ruler is top top the left, there is a pressure to the right, and also vice versa.

Consider, for example, plucking a plastic ruler presented in the very first figure. The deformation of the leader creates a force in opposing direction, known as a restoring force. Once released, the restoring force reasons the ruler to move earlier toward its steady equilibrium position, whereby the net force on it is zero. However, by the time the ruler gets there, it gains momentum and also continues to move to the right, developing the the opposite deformation. It is then compelled to the left, earlier through equilibrium, and also the process is recurring until dissipative forces (e.g., friction) dampen the motion. These pressures remove mechanical power from the system, gradually reducing the movement until the ruler comes to rest.

Restoring force, momentum, and equilibrium: (a) The plastic ruler has been released, and also the restoring force is return the ruler to the equilibrium position. (b) The net pressure is zero at the equilibrium position, however the ruler has momentum and also continues to move to the right. (c) The restoring force is in opposing direction. It stops the ruler and also moves it earlier toward equilibrium again. (d) now the ruler has actually momentum come the left. (e) In the absence of damping (caused by friction forces), the leader reaches its original position. Native there, the movement will repeat itself.

Hooke’s Law

The most basic oscillations take place when the restoring force is directly proportional to displacement. The name that was offered to this relationship in between force and also displacement is Hooke’s law:


Here, F is the restoring force, x is the displacement native equilibrium or deformation, and k is a consistent related come the difficulty in deforming the mechanism (often called the spring constant or pressure constant). Remember the the minus sign suggests the restoring pressure is in the direction opposite come the displacement. The force continuous k is related to the rigidity (or stiffness) the a system—the larger the force constant, the greater the restoring force, and the stiffer the system. The devices of k space newtons every meter (N/m). For example, k is straight related to Young’s modulus once we stretch a string. A typical physics laboratory practice is to measure up restoring forces produced by springs, identify if they monitor Hooke’s law, and calculate their pressure constants if lock do.

Mass ~ above a Spring

A common example of an objecting oscillating ago and forth according come a restoring force straight proportional to the displacement from equilibrium (i.e., adhering to Hooke’s Law) is the instance of a mass on the end of suitable spring, wherein “ideal” means that no messy real-world variables interfere v the imagined outcome.

The activity of a fixed on a spring can be defined as basic Harmonic movement (SHM), the name provided to oscillatory activity for a system where the net pressure can be described by Hooke’s law. We have the right to now determine how to calculation the duration and frequency of an oscillating fixed on the finish of suitable spring. The period T can be calculated learning only the mass, m, and also the force constant, k:

\textT=2\pi \sqrt\frac\textm\textk

When taking care of \textf=1/\textT, the frequency is provided by:

\textf=\frac12\pi \sqrt\frac\textk\textm

We deserve to understand the dependency of this equations on m and k intuitively. If one were to boost the fixed on an oscillating spring device with a given k, the boosted mass will certainly provide much more inertia, leading to the acceleration due to the restoring force F come decrease (recall Newton’s second Law: \textF=\textma). This will lengthen the oscillation duration and decrease the frequency. In contrast, increasing the force continuous k will rise the restoring force according to Hooke’s Law, in turn causing the acceleration at each displacement allude to also increase. This reduce the duration and rises the frequency. The best displacement indigenous equilibrium is known as the amplitude X.

Motion the a massive on an ideal spring: things attached to a feather sliding on a frictionless surface ar is one uncomplicated basic harmonic oscillator. As soon as displaced from equilibrium, the thing performs simple harmonic movement that has an amplitude X and a period T. The object’s maximum speed occurs together it passes with equilibrium. The stiffer the spring is, the smaller the duration T. The higher the mass of the object is, the higher the duration T. (a) The mass has accomplished its biggest displacement X come the right and also now the restoring pressure to the left is at its maximum magnitude. (b) The restoring force has moved the mass earlier to that is equilibrium point and is now equal to zero, however the leftward velocity is in ~ its maximum. (c) The mass’s inert has carried it come its best displacement come the right. The restoring pressure is currently to the right, equal in magnitude and also opposite in direction contrasted to (a). (d) The equilibrium allude is with again, this time with momentum come the right. (e) The bicycle repeats.

Key Takeaways

Key PointsSimple harmonic activity is regularly modeled v the instance of a massive on a spring, whereby the restoring force obey’s Hooke’s Law and also is directly proportional come the displacement of an object from that equilibrium position.Any device that obeys basic harmonic activity is known as a straightforward harmonic oscillator.The equation of activity that describes simple harmonic motion have the right to be derived by combining Newton’s second Law and also Hooke’s Law into a second-order linear ordinary differential equation: \textF_\textnet=\textm\frac\textd^2\textx\textdt^2=-\textkx.Key Termssimple harmonic oscillator: A maker that implements Hooke’s law, such as a mass the is attached come a spring, v the other end of the feather being linked to a strict support, such together a wall.oscillator: A pattern the returns come its initial state, in the same orientation and position, after a finite number of generations.

Simple Harmonic Motion

Simple harmonic activity is a type of periodic activity where the restoring force is straight proportional come the displacement (i.e., it complies with Hooke’s Law). It can serve together a mathematical version of a selection of motions, such as the oscillation of a spring. In addition, various other phenomena deserve to be approximated by simple harmonic motion, such as the activity of a simple pendulum, or molecule vibration.

Simple harmonic motion is typified by the activity of a massive on a spring once it is topic to the straight elastic restoring pressure given through Hooke’s Law. A mechanism that follows simple harmonic motion is recognized as a simple harmonic oscillator.

Dynamics of simple Harmonic Oscillation

For one-dimensional an easy harmonic motion, the equation of movement (which is a second-order linear ordinary differential equation with continuous coefficients) deserve to be obtained by method of Newton’s 2nd law and also Hooke’s law.


where m is the fixed of the oscillating body, x is the displacement native the equilibrium position, and k is the spring constant. Therefore:


Solving the differential equation above, a systems which is a sinusoidal role is obtained.

\textx(\textt)=\textc_1\textcos(\omega \textt)+\textc_2\textsin(\omega \textt)=\textAcos(\omega \textt - \varphi ),


\omega = \sqrt\frac\textk\textm,



In the solution, c1 and c2 space two constants determined by the early stage conditions, and the origin is set to it is in the equilibrium position. Every of this constants carries a physical an interpretation of the motion: A is the amplitude (maximum displacement native the equilibrium position), ω = 2πf is the angular frequency, and also φ is the phase.

We deserve to use differential calculus and find the velocity and acceleration as a function of time:

\textv(\textt)=\frac\textdx\textdt=-\textA\omega \textsin(\omega \textt-\varphi )

\texta(\textt)=\frac\textd^2\textx\textdt^2=-\textA\omega ^2\textcos(\omega \textt-\varphi ).

Acceleration can likewise be expressed as a function of displacement:

\texta(\textt)=-\omega ^2\textx.

Then due to the fact that ω = 2πf,

\textf=\frac12\pi \sqrt\frac\textk\textm.

Recalling the \textT=1/\textf,

\textT=2\pi \sqrt\frac\textm\textk.

Using Newton’s 2nd Law, Hooke’s Law, and some differential Calculus, us were may be to derive the period and frequency that the massive oscillating ~ above a feather that we encountered in the critical section! note that the duration and frequency are totally independent the the amplitude.

The listed below figure mirrors the simple harmonic motion of an item on a spring and presents graphs the x(t),v(t), and also a(t) matches time. Girlfriend should discover to develop mental connections in between the over equations, the different positions that the object on a feather in the cartoon, and the linked positions in the graphs that x(t), v(t), and a(t).

Visualizing basic Harmonic Motion: Graphs the x(t),v(t), and a(t) versus t for the motion of things on a spring. The net pressure on the object have the right to be described by Hooke’s law, and so the object undergoes an easy harmonic motion. Keep in mind that the initial position has the vertical displacement in ~ its maximum value X; v is at first zero and then negative as the object move down; and also the initial acceleration is negative, earlier toward the equilibrium position and becoming zero at the point.

Key Takeaways

Key PointsUniform one motion defines the activity of an item traveling a circular path with continuous speed. The one-dimensional projection of this motion can be described as simple harmonic motion.In uniform circular motion, the velocity vector v is constantly tangent to the circular course and consistent in magnitude. The acceleration is consistent in magnitude and also points to the center of the circular path, perpendicular to the velocity vector in ~ every instant.If an item moves v angular velocity ω around a one of radius r focused at the beginning of the x-y plane, then its motion along every coordinate is an easy harmonic movement with amplitude r and also angular frequency ω.Key Termscentripetal acceleration: Acceleration that renders a human body follow a bent path: it is constantly perpendicular to the velocity of a body and also directed towards the center of curvature of the path.uniform one motion: Movement approximately a circular path with constant speed.

Uniform one Motion

Uniform circular motion describes the activity of a body traversing a circular route at continuous speed. The distance of the human body from the facility of the one remains constant at all times. Despite the body’s speed is constant, that velocity is not constant: velocity (a vector quantity) counts on both the body’s speed and also its direction the travel. Due to the fact that the body is constantly transforming direction as it travels about the circle, the velocity is an altering also. This varying velocity shows the existence of an acceleration referred to as the centripetal acceleration. Centripetal acceleration is of continuous magnitude and directed at all times in the direction of the facility of the circle. This acceleration is, in turn, developed by a centripetal force —a force in continuous magnitude, and also directed towards the center.


The above figure illustrates velocity and acceleration vectors for uniform motion at four various points in the orbit. Since velocity v is tangent to the circular path, no two velocities allude in the very same direction. Back the object has a continuous speed, the direction is constantly changing. This readjust in velocity is as result of an acceleration, a, whose magnitude is (like the of the velocity) organized constant, however whose direction likewise is constantly changing. The acceleration clues radially inwards (centripetally) and is perpendicular come the velocity. This acceleration is well-known as centripetal acceleration.


Uniform Circular motion (at 4 Different suggest in the Orbit): Velocity v and acceleration a in uniform circular motion at angular price ω; the rate is constant, yet the velocity is always tangent come the orbit; the acceleration has continuous magnitude, but always points toward the center of rotation

Displacement approximately a circular path is regularly given in regards to an angle θ. This angle is the angle in between a directly line drawn from the center of the circle to the objects starting position ~ above the edge and also a right line attracted from the objects finishing position on the leaf to center of the circle. View for a visual depiction of the angle wherein the allude p started on the x- axis and moved come its present position. The angle θ describes how much it moved.

Projection that Uniform circular Motion: A point P moving on a circular route with a continuous angular velocity ω is undergoing uniform circular motion. Its projection on the x-axis undergoes an easy harmonic motion. Also shown is the velocity the this point around the circle, v−max, and its projection, i beg your pardon is v. Note that these velocities form a similar triangle come the displacement triangle.

For a path about a one of radius r, when an angle θ (measured in radians ) is brushed up out, the distance traveled ~ above the edge of the one is s = rθ. You can prove this you yourself by remembering that the one of a one is 2*pi*r, so if the thing traveled approximately the whole circle (one circumference) the will have actually gone with an edge of 2pi radians and traveled a street of 2pi*r. Therefore, the rate of travel approximately the orbit is:

\textv=\textr\frac\textd\theta \textdt=\textr\omega,

where the angular rate of rotation is ω. (Note that ω = v/r. ) Thus, v is a constant, and also the velocity vector v also rotates with constant magnitude v, in ~ the very same angular rate ω.


The acceleration in uniform circular motion is always directed inward and is offered by:

\texta=\textv\frac\textd\theta \textdt=\textv\omega =\frac\textv^2\textr.

This acceleration plot to readjust the direction of v, but not the speed.

Simple Harmonic movement from Uniform circular Motion

There is one easy method to produce basic harmonic activity by making use of uniform circular motion. The figure below demonstrates one method of making use of this method. A ball is attached come a uniformly rotating upright turntable, and its zero is projected ~ above the floor together shown. The shadow undergoes simple harmonic motion.

Shadow that a sphere Undergoing an easy Harmonic Motion: The zero of a ball rotating at continuous angular velocity ω top top a turntable goes ago and forth in an accurate simple harmonic motion.

The next number shows the simple relationship between uniform circular motion and simple harmonic motion. The point P travels around the circle at constant angular velocity ω. The suggest P is analogous come the ball on a turntable in the figure above. The forecast of the position of P onto a fixed axis undergoes an easy harmonic motion and is analogous to the shadow of the object. In ~ a allude in time presume in the figure, the projection has actually position x and also moves to the left through velocity v. The velocity of the allude P about the circle equals |vmax|. The projection of |vmax| top top the x-axis is the velocity v of the straightforward harmonic activity along the x-axis.

To check out that the projection undergoes straightforward harmonic motion, keep in mind that its place x is offered by:


where θ=ωt, ω is the consistent angular velocity, and also X is the radius that the circular path. Thus,

\textx=\textXcos\omega \textt.

The angular velocity ω is in radians every unit time; in this instance 2π radians is the time for one revolution T. That is, ω=2π/T. Substituting this expression because that ω, we see that the position x is provided by:

\textx(\textt)=\textcos(\frac2\pi \textt\textT)=\textcos(2\pi \textft).

Note: This equation have to look acquainted from ours earlier discussion of straightforward harmonic motion.

The basic Pendulum

A an easy pendulum acts favor a harmonic oscillator through a period dependent only on L and g for sufficiently little amplitudes.

Key Takeaways

Key PointsA straightforward pendulum is defined as things that has a small mass, likewise known together the pendulum bob, i m sorry is suspended indigenous a wire or wire of negligible mass.When displaced, a pendulum will certainly oscillate around its equilibrium allude due to inert in balance v the restoring force of gravity.When the swings ( amplitudes ) are small, less than around 15º, the pendulum acts together a straightforward harmonic oscillator with period \textT=2\pi \sqrt\frac\textL\textg, whereby L is the length of the string and also g is the acceleration as result of gravity.Key Termssimple pendulum: A hypothetical pendulum consisting of a weight suspended by a weightless string.

The basic Pendulum

A pendulum is a weight suspended indigenous a pivot so that it can swing freely. When a pendulum is displaced party from its resting equilibrium position, that is topic to a restoring force; after it reaches that is highest suggest in the swing, gravity will certainly accelerate it back toward the equilibrium position. When released, the restoring force an unified with the pendulum’s mass reasons it come oscillate around the equilibrium position, swinging back and forth.

Simple Pendulum: A straightforward pendulum has actually a small-diameter bob and also a string that has a very small mass but is solid enough not to stretch appreciably. The direct displacement from equilibrium is s, the length of the arc. Also shown space the forces on the bob, which result in a net force of −mgsinθ towards the equilibrium position—that is, a restoring force.

For tiny displacements, a pendulum is a an easy harmonic oscillator. A simple pendulum is identified to have an item that has actually a tiny mass, also known as the pendulum bob, which is suspended indigenous a cable or cable of negligible mass, together as presented in the illustrating figure. Exploring the an easy pendulum a little further, us can uncover the problems under which that performs straightforward harmonic motion, and we deserve to derive an exciting expression for its period.

We start by defining the displacement to be the arc size s. We view from the number that the net force on the bob is tangent come the arc and equals −mgsinθ. (The weight mg has materials mgcosθ follow me the string and also mgsinθ tangent to the arc. ) tension in the string exactly cancels the ingredient mgcosθ parallel to the string. This pipeline a net restoring force illustration the pendulum ago toward the equilibrium position at θ = 0.

Now, if us can show that the restoring force is straight proportional come the displacement, then we have actually a an easy harmonic oscillator. In trying to recognize if we have actually a simple harmonic oscillator, we have to note the for tiny angles (less than around 15º), sinθθ (sinθ and also θ differ by about 1% or much less at smaller sized angles). Thus, for angles less than around 15º, the restoring force F is

\textF\approx -\textmg\theta.

The displacement s is directly proportional come θ. When θ is express in radians, the arc length in a one is pertained to its radius (L in this instance) by:


so that


For small angles, then, the expression because that the restoring pressure is:

\textF\approx \frac\textmgL\texts.

This expression is the the kind of Hooke’s Law:

\textF\approx -\textkx

where the force continuous is provided by k=mg/L and the displacement is given by x=s. For angles much less than about 15º, the restoring pressure is straight proportional come the displacement, and the straightforward pendulum is a basic harmonic oscillator.

Using this equation, us can find the period of a pendulum for amplitudes much less than about 15º. Because that the basic pendulum:

\textT=2\pi \sqrt\frac\textm\textk=2\pi\sqrt\frac\textm\frac\textmg\textL.


\textT=2\pi \sqrt\frac\textL\textg

or the period of a simple pendulum. This an outcome is interesting due to the fact that of that simplicity. The only things that influence the duration of a an easy pendulum are its length and also the acceleration due to gravity. The duration is fully independent of other factors, such as mass. Even straightforward pendulum clocks deserve to be carefully adjusted and also accurate. Note the dependence of T ~ above g. If the size of a pendulum is specifically known, it have the right to actually be provided to measure up the acceleration due to gravity. If θ is much less than about 15º, the duration T because that a pendulum is almost independent that amplitude, as with straightforward harmonic oscillators. In this case, the activity of a pendulum as a duty of time deserve to be modeled as:

\theta (\textt)=\theta _\texto\textcos(\frac2\pi \textt\textT)

For amplitudes larger than 15º, the period increases slowly with amplitude so it is longer than provided by the basic equation for T above. Because that example, at an amplitude that θ0 = 23° the is 1% larger. The period increases asymptotically (to infinity) together θ0 approaches 180°, due to the fact that the value θ0 = 180° is an rough equilibrium allude for the pendulum.

The physical Pendulum

The period of a physics pendulum relies upon its minute of inertia about its pivot suggest and the distance from its facility of mass.

Key Takeaways

Key PointsA physics pendulum is the generalized instance of the straightforward pendulum. It is composed of any type of rigid body that oscillates around a pivot point.For small amplitudes, the period of a physical pendulum only depends on the moment of inertia that the body around the pivot point and the street from the pivot to the body’s facility of mass. It is calculation as: \textT=2\pi \sqrt\frac\textI\textmgh.The period is quiet independent that the full mass of the strictly body. However, that is no independent the the mass circulation of the strictly body. A change in shape, size, or mass circulation will adjust the moment of inertia and also thus, the period.Key Termsphysical pendulum: A pendulum wherein the rod or cable is not massless, and may have prolonged size; that is, an arbitrarily-shaped, rigid human body swinging through a pivot. In this case, the pendulum’s period depends on its moment of inertia about the pivot point.mass distribution: explains the spatial distribution, and also defines the center, of massive in an object.

The physical Pendulum

Recall the a simple pendulum is composed of a fixed suspended indigenous a massless wire or rod on a frictionless pivot. In the case, we room able to neglect any kind of effect indigenous the string or stick itself. In contrast, a physical pendulum (sometimes referred to as a compound pendulum) may be suspended by a rod the is not massless or, much more generally, may be an arbitrarily-shaped, rigid human body swinging by a pivot (see ). In this case, the pendulum’s period depends ~ above its minute of inertia roughly the pivot point.

A physics Pendulum: an instance showing how forces act through facility of mass. We have the right to calculate the duration of this pendulum by determining the moment of inertia of the object about the pivot point.

Gravity acts with the facility of massive of the strict body. Hence, the size of the pendulum offered in equations is same to the linear distance between the pivot and also the facility of massive (h).

The equation of speak gives:


where α is the angular acceleration, τ is the torque, and I is the minute of inertia.

The speak is produced by gravity so:


where h is the distance from the center of mass come the pivot point and θ is the edge from the vertical.

Hence, under the small-angle approximation sin\theta \approx \theta,

\alpha\approx -\frac\textmgh\theta \textI.

This is that the same kind as the conventional an easy pendulum and also this gives a period of:

\textT=2\pi \sqrt\frac\textI\textmgh.

And a frequency of:

\textf=\frac1\textT=\frac12\pi \sqrt\frac\textmgh\textI.

In instance we recognize the minute of inertia of the strictly body, we can evaluate the above expression of the period for the physics pendulum. Because that illustration, let us consider a uniform strict rod, pivoted native a framework as displayed (see ). Clearly, the facility of massive is in ~ a distance L/2 native the point of suspension:

Uniform rigid Rod: A strict rod with uniform mass circulation hangs indigenous a pivot point. This is an additional example the a physics pendulum.


The moment of inertia that the strict rod about its facility is:


However, we must evaluate the minute of inertia around the pivot point, not the facility of mass, so we apply the parallel axis theorem:


Plugging this result into the equation because that period, we have:

\textT=2\pi \sqrt\frac\textI\textmgh=2\pi\sqrt\frac2\textmL^23\textmgL=2\pi\sqrt\frac2\textL3\textg.

The vital thing to note around this relation is the the duration is still independent the the massive of the strict body. However, the is no independent the the mass distribution of the strictly body. A readjust in shape, size, or mass distribution will change the minute of inertia. This, in turn, will adjust the period.

As through a simple pendulum, a physics pendulum can be supplied to measure up g.

Energy in a simple Harmonic Oscillator

The total energy in a an easy harmonic oscillator is the continuous sum the the potential and kinetic energies.

Key Takeaways

Key PointsThe sum of the kinetic and also potential energies in a straightforward harmonic oscillator is a constant, i.e., KE+PE=constant. The power oscillates ago and forth between kinetic and also potential, going fully from one come the other as the device oscillates.In a feather system, the conservation equation is written as: \frac12\textmv^2+\frac12\textkx^2=constant=\frac12\textkX^2, wherein X is the best displacement.The preferably velocity depends on 3 factors: amplitude, the stiffness factor, and mass: \textv_\textmax=\sqrt\frac\textk\textm\textX.Key Termselastic potential energy: The power stored in a deformable object, such as a spring.dissipative forces: forces that reason energy to be shed in a device undergoing motion.

Energy in a an easy Harmonic Oscillator

To examine the power of a basic harmonic oscillator, we very first consider all the develops of power it can have. Recall that the potential power (PE), save on computer in a feather that follows Hooke’s law is:


where PE is the potential energy, k is the spring constant, and x is the size of the displacement or deformation. Since a simple harmonic oscillator has no dissipative forces , the various other important type of energy is kinetic energy (KE). Preservation of energy for these two creates is:


which have the right to be composed as:


This statement of preservation of energy is valid because that all an easy harmonic oscillators, including ones where the gravitational pressure plays a role. For example, because that a basic pendulum we change the velocity with v=, the spring consistent with k=mg/L, and the displacement term v x=. Thus:

\frac12\textmL^2\omega ^2+\frac12\textmgL\theta ^2=\textconstant.

In the situation of undamped, basic harmonic motion, the power oscillates earlier and forth in between kinetic and also potential, going fully from one to the various other as the system oscillates. So for the basic example of an object on a frictionless surface attached come a spring, as displayed again (see ), the activity starts with every one of the power stored in the spring. As the thing starts to move, the elastic potential energy is converted to kinetic energy, ending up being entirely kinetic energy at the equilibrium position. The is climate converted earlier into elastic potential energy by the spring, the velocity i do not care zero as soon as the kinetic energy is completely converted, and also so on. This concept provides extra insight here and also in later applications of basic harmonic motion, together as alternative current circuits.

Energy in a straightforward Harmonic Oscillator: The transformation of energy in basic harmonic movement is illustrated for things attached come a spring on a frictionless surface. (a) The mass has completed maximum displacement indigenous equilibrium. All power is potential energy. (b) together the fixed passes v the equilibrium allude with maximum speed all energy in the system is in kinetic energy. (c) when again, all energy is in the potential form, stored in the compression of the spring (in the an initial panel the power was save on computer in the expansion of the spring). (d) Passing through equilibrium again all power is kinetic. (e) The mass has completed whole cycle.

The preservation of power principle have the right to be provided to derive an expression for velocity v. If we begin our straightforward harmonic motion with zero velocity and also maximum displacement (x=X), climate the complete energy is:


This complete energy is constant and is shifted ago and forth in between kinetic energy and also potential energy, at most times being shared by each. The conservation of power for this system in equation form is thus:


Solving this equation because that v yields:

\textv=\pm \sqrt\frac\textk\textm(\textX^2-\textx^2).

Manipulating this expression algebraically gives:

\textv=\pm \sqrt\frac\textk\textm\textX\sqrt1-\frac\textx^2\textX^2,

and so:

\textv=\pm \textv_\textmax\sqrt1-\frac\textx^2\textX^2,



From this expression, we view that the velocity is a maximum (vmax) at x=0. notice that the maximum velocity relies on three factors. The is straight proportional to amplitude. As you might guess, the greater the maximum displacement, the greater the best velocity. The is additionally greater for stiffer systems due to the fact that they exert greater pressure for the very same displacement. This observation is watched in the expression for vmax; that is proportional come the square root of the force continuous k. Finally, the best velocity is smaller sized for objects that have actually larger masses, because the best velocity is inversely proportional come the square source of m. Because that a offered force, objects that have large masses accelerate more slowly.

A similar calculation because that the an easy pendulum to produce a comparable result, namely:

\omega_\textmax=\sqrt\frac\textg\textL\theta _\textmax.

Key Takeaways

Key PointsFor basic harmonic oscillators, the equation of motion is constantly a second order differential equation that relates the acceleration and also the displacement. The pertinent variables room x, the displacement, and k, the feather constant.Solving the differential equation over always produces solutions that are sinusoidal in nature. Because that example, x(t), v(t), a(t), K(t), and U(t) all have sinusoidal solutions for an easy harmonic motion.Uniform circular movement is additionally sinusoidal due to the fact that the forecast of this activity behaves like a straightforward harmonic oscillator.Key Termssinusoidal: In the form of a wave, particularly one who amplitude different in proportion come the sine of part variable (such together time).

Sinusoidal Nature of straightforward Harmonic Motion

Why room sine tide so common?

If the fixed -on-a-spring system debated in ahead sections were to it is in constructed and its activity were measure up accurately, its xt graph would certainly be a near-perfect sine-wave shape, as presented in. That is called a “sine wave” or “sinusoidal” also if that is a cosine, or a sine or cosine shifted by part arbitrary horizontal amount. It may not it is in surprising the it is a wiggle the this basic sort, however why is it a particular mathematically perfect shape? Why is it no a sawtooth shape, like in (2); or some various other shape, favor in (3)? that is notable that a vast variety of apparently unrelated vibrating systems present the exact same mathematical feature. A tuning fork, a sapling pulled to one side and also released, a auto bouncing top top its shock absorbers, all these systems will exhibit sine-wave activity under one condition: the amplitude of the activity must be small.

Sinusoidal and also Non-Sinusoidal Vibrations: just the optimal graph is sinusoidal. The others vary with consistent amplitude and period, however do no describe straightforward harmonic motion.

Hooke’s Law and also Sine tide Generation

The an essential to understanding how an item vibrates is to know just how the pressure on the object counts on the object’s position. If a system complies with Hooke’s Law, the restoring force is proportional come the displacement. Together touched ~ above in previous sections, over there exists a second order differential equation that relates acceleration and displacement.


When this basic equation is fixed for the position, velocity and also acceleration together a duty of time:

\textx(\textt)=\textAcos(\omega \textt-\varphi )\textv(\textt)=\frac\textdx\textdt=-\textA\omega \textsin(\omega \textt-\varphi )\texta(\textt)=\frac\textd^2\textx\textdt^2=-\textA\omega^2 \textcos(\omega \textt-\varphi )

These are all sinusoidal solutions. Think about a massive on a spring that has a tiny pen within running across a moving strip of paper as it bounces, recording its movements.

Mass on Spring producing Sine Wave: The vertical place of an item bouncing ~ above a feather is tape-recorded on a strip of relocating paper, leave a sine wave.

The over equations have the right to be rewritten in a form applicable to the variables for the massive on spring system in the figure.

\textx(\textt)=\textXcos(\frac2\pi \textt\textT)\textv(\textt)=-\textv_\textmax\textsin(\frac2\pi \textt\textT)\texta(\textt)=-\frac\textkX\textm\textcos(\frac2\pi \textt\textT)

Recall the the projection of uniform circular motion deserve to be explained in regards to a basic harmonic oscillator. Uniform circular activity is therefore also sinusoidal, as you can see from.

Sinusoidal Nature the Uniform circular Motion: The position of the forecast of uniform circular movement performs simple harmonic motion, as this wavelike graph the x matches t indicates.

Instantaneous energy of simple Harmonic Motion

The equations discussed for the components of the total energy of an easy harmonic oscillators may be combined with the sinusoidal solutions for x(t), v(t), and a(t) to design the changes in kinetic and potential energy in an easy harmonic motion.

The kinetic power K the the mechanism at time t is:

\textK(\textt)=\frac12\textmv^2(\textt)=\frac12\textm\omega ^2\textA^2\textsin^2(\omega \textt-\varphi )=\frac12\textkA^2\textsin^2(\omega \textt-\varphi ).

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The potential power U is:

\textU(\textt)=\frac12\textkx^2(\textt)==\frac12\textkA^2\textcos^2(\omega \textt-\varphi ).