An object relocating along the x-axis is stated to exhibit **simple harmonic motion** if its position as a role of time varies together

x(t) = x0 + A cos(ωt + φ).

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The object oscillates about the equilibrium place x0. If we choose the beginning of ours coordinate system such that x0 = 0, climate the displacement x indigenous the equilibrium position as a role of time is given by

x(t) = A cos(ωt + φ).

A is the **amplitude** the the oscillation, i.e. The maximum displacement that the thing from equilibrium, one of two people in the optimistic or an adverse x-direction. Straightforward harmonic movement is repetitive. The **period**T is the time it take away the object to complete one oscillation and also return come the beginning position. The**angular frequency** ω is provided by ω = 2π/T. The angular frequency is measure in radians per second. The train station of the period is the **frequency **f = 1/T. The frequency f = 1/T = ω/2π the the motion gives the variety of complete oscillations every unit time. That is measure up in systems of Hertz, (1 Hz = 1/s).

The velocity of the object together a duty of time is given by

v(t) = -ω A sin(ωt + φ),

and the acceleration is provided by

a(t) = -ω2A cos(ωt + φ) = -ω2x.

The amount φ is called the **phase constant**. That is established by the initial conditions of the motion. If at t = 0 the object has actually its best displacement in the confident x-direction, then φ = 0, if it has actually its best displacement in the negative x-direction, climate φ = π. If at t = 0 the fragment is moving through that equilibrium place with best velocity in the negative x-direction climate φ = π/2. The amount ωt + φ is dubbed the **phase**.

In the figure listed below position and also velocity room plotted together a function of time for oscillatory activity with a duration of 5 s. The amplitude and also the maximum velocity have arbitrary units. Position and velocity are **out of phase**. The velocity is zero in ~ maximum displacement, and also the displacement is zero at maximum speed.

**For basic harmonic motion, the acceleration a = -ω2x is proportional to the displacement, but in the contrary direction. An easy harmonic activity is accelerated motion.** If an object exhibits an easy harmonic motion, a pressure must be exhilaration on the object. The pressure is

F = ma = -mω2x.

It obeys **Hooke"s law**, F = -kx, through k = mω2.

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The pressure exerted through a feather obeys Hooke"s law. I think that an item is attached to a spring, which is extended or compressed. Climate the feather exerts a force on the object. This force is proportional come the displacement x the the feather from the equilibrium position and also is in a direction opposite come the displacement.

F** **= -kx

Assume the spring is stretched a distance A native its equilibrium position and also then released. The object attached to the spring increases as that moves back towards the equilibrium position.

a** **= -(k/m)x

It gains speed as the moves in the direction of the equilibrium position due to the fact that its acceleration is in the direction the its velocity. When it is in ~ the equilibrium position, the acceleration is zero, but the object has actually maximum speed. It overshoots the equilibrium position and also starts slow down, because the acceleration is now in a direction opposite come the direction of its velocity. Neglecting friction, it pertains to a stop when the spring is compressed through a street A and also then increases back in the direction of the equilibrium position. The again overshoots and also comes to a protect against at the initial position once the spring is stretched a street A. The activity repeats. The thing oscillates earlier and forth. That executes an easy harmonic motion. The angular frequency that the activity is

ω = √(k/m),

the period is

T = 2π√(m/k),

and the frequency is

f = (1/(2π))√(k/m).

## Summary:If the only force acting on things with massive m is a Hooke"s legislation force,F = -kxthen the motion of the thing is simple harmonic motion. With x being the displacement from equilibrium we have x(t) = Acos(ωt + φ),v(t) = -ωAsin(ωt + φ),a(t) = -ω2Acos(ωt + φ) = -ω2x.ω = (k/m)½ = 2πf = 2π/T. A = amplitudeω = angular frequencyf = frequencyT = periodφ = phase constant |

A fragment oscillates with an easy harmonic motion, so the its displacement different according come the expression x = (5 cm)cos(2t + π/6) wherein x is in centimeters and also t is in seconds. In ~ t = 0 find(a) the displacement that the particle,(b) its velocity, and(c) that acceleration.(d) uncover the duration and amplitude of the motion.

Solution:

Reasoning:Analyze basic harmonic motion.x(t) = A cos(ωt + φ). A = amplitude, ω = angular frequency, φ = step constant.v(t) = -ω A sin(ωt + φ), a(t) = -ω2A cos(ωt + φ) = -ω2x.Details of the calculation:(a) The displacement together a duty of time is x(t) = Acos(ωt + φ). Right here ω = 2/s, φ = π/6, and also A = 5 cm. The displacement at t = 0 is x(0) = (5 cm)cos(π/6) = 4.33 cm.(b) The velocity in ~ t = 0 is v(0) = -ω(5 cm)sin(π/6) = -5 cm/s.(c) The acceleration at t = 0 is a(0) = -ω2(5 cm)cos(π/6) = -17.3 cm/s2.(d) The duration of the movement is T = 2π/ω = π s, and also the amplitude is 5 cm.Problem:A 20 g bit moves in straightforward harmonic activity with a frequency of 3 oscillations per second and an amplitude the 5 cm.(a) v what total distance walk the particle move during one bike of that motion?(b) What is its preferably speed? where does the occur?(c) uncover the preferably acceleration of the particle. Wherein in the motion does the preferably acceleration occur?

Solution:

Reasoning:Analyze straightforward harmonic motion, x(t) = A cos(ωt + φ).Details of the calculation:(a) The full distance d the bit moves during one bike is indigenous x = -A to x = +A and earlier to x = -A, therefore d = 4A = 20 cm.(b) The maximum speed of the bit is vmax = ωA = 2πfA = 2π 15 cm/s = 0.94 m/s. The particle has actually maximum speed once it passes with the equilibrium position.(c) The maximum acceleration that the fragment is amax = ω2A = (2πf)2A = 17.8 m/s2.The particle has maximum acceleration at the turning points, wherein it has actually maximum displacement.Assume a fixed suspended indigenous a vertical spring of spring constant k. In equilibrium the spring is stretched a distance x0 = mg/k. If the massive is displaced native equilibrium position downward and the feather is stretched secondary distance x, then the full force ~ above the fixed is mg - k(x0+ x) = -kx directed in the direction of the equilibrium position. If the fixed is displaced increase by a distance x, climate the full force on the fixed is mg - k(x0- x) = kx, directed in the direction of the equilibrium position. The mass will execute basic harmonic motion. The angular frequency ω = SQRT(k/m) is the same for the massive oscillating ~ above the feather in a vertical or horizontal position. But the equilibrium length of the spring about which the oscillates is different for the upright position and the horizontal position.

Assume things attached come a spring exhibits straightforward harmonic motion. Permit one finish of the feather be attached come a wall surface and let the object move horizontally on a frictionless table.

### What is the complete energy of the object?

The object"s kinetic energy is

K = ½mv2 = ½mω2A2sin2(ωt + φ).

Its potential power is elastic potential energy. The elastic potential power stored in a spring displaced a street x native its equilibrium place is U = ½kx2. The object"s potential energy as such is

U = ½kx2 = ½mω2x2 = ½mω2A2cos2(ωt + φ).

The complete mechanical power of the thing is

E = K + U = ½mω2A2(sin2(ωt + φ) + cos2(ωt + φ)) = ½mω2A2.

The power E in the mechanism is proportional come the **square the the amplitude**.

E = ½kA2.

It is a continuously changing mixture of kinetic energy and potential energy.

For any object executing an easy harmonic movement with angular frequency ω, the restoring pressure F = -mω2x obeys Hooke"s law, and therefore is a **conservative force**. We can specify a potential power U = ½mω2x2, and the full energy the the thing is provided by E = ½mω2A2. Due to the fact that vmax = ωA, we can additionally write E = ½mvmax2.

A bit that hangs indigenous a feather oscillates with an angular frequency the 2 rad/s. The feather is suspended from the ceiling of an elevator car and also hangs motionless (relative come the car) as the vehicle descends in ~ a consistent speed of 1.5 m/s. The car then suddenly stops. Overlook the massive of the spring.With what amplitude walk the fragment oscillate?

Solution:

Reasoning:When traveling in the elevator at constant speed, the total force top top the fixed is zero. The pressure exerted by the spring is equal in size to the gravitational force on the mass, the spring has the equilibrium length of a upright spring. When the elevator all of sudden stops, the end of the feather attached come the ceiling stops. The mass, but has momentum, ns = mv, and therefore starts stretching the spring. The moves with the equilibrium position of the vertical spring v its maximum velocity vmax= 1.5 m/s.Its velocity as a duty of time is v(t) = -ωAsin(ωt + φ). Details of the calculation:Since vmax = ωA and ω = 2/s, the amplitude the the amplitude that the oscillations is A = 0.75 m.Problem:A mass-spring device oscillates v an amplitude that 3.5 cm. If the force consistent of the spring of 250 N/m and the fixed is 0.5 kg, determine(a) the mechanical power of the system,(b) the maximum rate of the mass, and(c) the best acceleration.

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Solution:

Reasoning:The mechanical energy of a system executing basic harmonic movement is E = ½kA2 = ½mω2A2.Details that the calculation:(a) We have m = 0.5 kg, A = 0.035 m, k = 250 N/m, ω2 = k/m = 500/s2, ω = 22.36/s.The mechanical energy of the device is E = ½kA2 = 0.153 J.(b) The maximum speed of the massive is vmax = ωA = 0.78 m/s.(c) The maximum acceleration is amax = ω2A = 17.5 m/s2.