# Pendulum uniform circular motion-A simple pendulum and circular motion | thecuriousastronomer

The swinging back and forth of a pendulum is an example of a very important type of motion which crops up in many places in Nature, so called Simple Harmonic Motion SHM. In this blog I will derive the basic equations of SHM, and then go on and talk about the deep connection between SHM and circular motion. If we start off by looking at a simple pendulum which has been displaced so that the bob is to the right of the vertical position, the angle the line of the pendulum makes with the vertical is given by , and for this derivation to work needs to be small. A simple pendulum will swing back and forth, exhibiting Simple Harmonic Motion. The force restoring the pendulum bob back to the middle, which I have called in the diagram above, is given by the minus sign comes about because the the force is back towards the centre, even though the angle increases as we move the bob to the right.

If the car is moving on a circular arc, then it is accelerating. Thus, Our final discussion will pertain to the period of the pendulum. Mass m 1 pulls on mass m 2and mass m 2 pulls on mass m 1. It is mtion from Eq.

## Tennessee amateur hardcore. Uniform circular motion

Pendulum A: A g mass attached to a 1. By so doing, the experimenters were able to investigate the possible effect of the mass upon the period. The form of potential energy possessed by a pendulum bob is gravitational potential energy. That's why. So what forces act upon a pendulum bob? The 4th Pendulkm is angular velocity squared? Clause B is easy, same as the other exercise getting Penduum back to statics : That's my thing! Both its direction and its magnitude change as the bob swings to and fro. So it would be logical to conclude that as the Pendulum uniform circular motion decreases along the arc motipn A to Dthe velocity increases. Our final discussion will pertain to the period of the pendulum. The height of the bar is proportional to the amount of that form of Pendulum uniform circular motion. The total mechanical energy is everywhere the same since energy is conserved by a pendulum.

Figure 1.

- What's new.
- Earlier in this lesson we learned that an object that is vibrating is acted upon by a restoring force.
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In order for an object to travel in a circular path, an unbalanced central force must be exerted upon it. Otherwise, the object would continue to travel along a straight-line path based on its inertia. Magnetism is a non-mechanical force that provides the necessary force to cause charged particles to travel in circular paths. Example 1: Strings and Flat Surfaces. Suppose that a mass is tied to the end of a string and is being whirled in a circle along the top of a frictionless table as shown in the diagram below.

A freebody diagram of the forces on the mass would show. Refer to the following information for the next two questions. Suppose a gram mass is being whirled in a circular path by a string on the surface of a smooth table. If the maximum tensile strength in the string is 10 N, how fast would the mass slide along the table when the radius of its path equals 40 cm? Example 2: Conical Pendulums. A freebody diagram of the mass on the end of the pendulum would show the following forces.

Refer to the following information for the next four questions. Suppose a gram ball is being whirled as a conical pendulum by a child. The ball is attached to a cm string and tracks out a horizontal circle with a radius of 40 cm.

What is the tension in the rope? How fast is the ball traveling as it swings? How many revolutions does the stopper complete each second? Example 3: Flat Curves. Many times, friction is the source of the centripetal force. A freebody diagram of this situation would look very much like that of the block on the end of a string, except that friction would replace tension.

Refer to the following information for the next three questions. What is the correspondingly minimal coefficient of friction between the road surface and the car's tires? How would this coefficient of friction be changed if a kg pickup truck were traveling through the same curve?

Example 4: Banked Curves. A freebody diagram of the forces acting on the car would show weight and a normal. Since the car is not sliding down the bank of the incline, but is instead traveling across the incline, components of the normal are examined. This component of the normal is supplying the centripetal force necessary to keep the car moving through the banked curve. At this critical speed, there is no need for any friction between the car and the road's surface.

If the speed of the car were to exceed v critical then the car would drift up the incline. If the speed of the car is less than v critical then the car would slip down the incline. Does your answer to the previous question depend on the mass of the car? Example 5: Gravitation and Satellites. Another major category of forces that produce uniform circular motion is gravitation.

This speed can also be expressed as. Communication satellites orbiting the Earth have a period of 24 hours so that they remain geosynchronous. Use these statistics as well as the following constants to answer the next series of questions:. How fast are geosynchronous satellites moving? Standard pendulums are not included in this lesson since they are not examples of uniform circular motion.

They are part of a larger category of behaviors known as vertical circular motion. How many revolutions would it make is 60 seconds? Resource Lesson:. Colwell All rights reserved.

I like Serena Homework Helper. Pendulum and circular motion. The above analysis applies for a single location along the pendulum's arc. First, observe the diagram for when the bob is displaced to its maximum displacement to the right of the equilibrium position. Using this reference frame, the equilibrium position would be regarded as the zero position. Since the motion of the object is momentarily paused , there is no need for a centripetal force.

### Pendulum uniform circular motion.

Because, to find what they ask of me tension at pendulum don't I need to find the normal force? And doesn't that mean sum of all forces? Now that I got V I'm a little bit hesitant how to continue. And at what point of the trajectory will these forces generate the greatest tension in the pendulum? Finally, how large will these forces be at that point? EDIT: As for your previous calculations I'm missing A little more of you! T is the time for a complete revolution of a uniform circular motion.

It's a pity that the hammer just falls and breaks something and is not neatly swinging around at an even speed to break something else. The formula you need is the one that relates the required centripetal force to speed and radius.

Did I get it? Clause B is easy, same as the other exercise getting me back to statics : That's my thing! More destruction! And we were given this list of formulas. The 4th one is angular velocity squared?

I'm not sure what is that. And the last one Not even sure what's that either. But I need a formula I'm sure of : Thanks to you. I'll use it. Last edited: May 26, Almost, but there are 2 forces: the tensile force and the force of gravity.

The resultant force must be equal to the centripetal force. However, this means the tensile force is a little bigger! Related Threads for: Uniform circular motion with a pendulum Pendulum with circular motion. Posted Apr 8, Replies 17 Views 2K. Uniform Circular Motion with friction. Posted Nov 8, Replies 2 Views 2K.

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We will expand on that discussion here as we make an effort to associate the motion characteristics described above with the concepts of kinetic energy , potential energy and total mechanical energy.

The kinetic energy possessed by an object is the energy it possesses due to its motion. It is a quantity that depends upon both mass and speed. The equation that relates kinetic energy KE to mass m and speed v is.

The faster an object moves, the more kinetic energy that it will possess. We can combine this concept with the discussion above about how speed changes during the course of motion. This blending of concepts would lead us to conclude that the kinetic energy of the pendulum bob increases as the bob approaches the equilibrium position. And the kinetic energy decreases as the bob moves further away from the equilibrium position. The potential energy possessed by an object is the stored energy of position.

Two types of potential energy are discussed in The Physics Classroom Tutorial - gravitational potential energy and elastic potential energy. Elastic potential energy is only present when a spring or other elastic medium is compressed or stretched. A simple pendulum does not consist of a spring. The form of potential energy possessed by a pendulum bob is gravitational potential energy. The amount of gravitational potential energy is dependent upon the mass m of the object and the height h of the object.

The equation for gravitational potential energy PE is. The height of an object is expressed relative to some arbitrarily assigned zero level. In other words, the height must be measured as a vertical distance above some reference position. For a pendulum bob, it is customary to call the lowest position the reference position or the zero level.

So when the bob is at the equilibrium position the lowest position , its height is zero and its potential energy is 0 J. As the pendulum bob does the back and forth , there are times during which the bob is moving away from the equilibrium position.

As it does, its height is increasing as it moves further and further away. It reaches a maximum height as it reaches the position of maximum displacement from the equilibrium position. As the bob moves towards its equilibrium position, it decreases its height and decreases its potential energy.

Now let's put these two concepts of kinetic energy and potential energy together as we consider the motion of a pendulum bob moving along the arc shown in the diagram at the right. We will use an energy bar chart to represent the changes in the two forms of energy.

The amount of each form of energy is represented by a bar. The height of the bar is proportional to the amount of that form of energy. The TME bar represents the total amount of mechanical energy possessed by the pendulum bob. The total mechanical energy is simply the sum of the two forms of energy — kinetic plus potential energy. What do you notice? When you inspect the bar charts, it is evident that as the bob moves from A to D, the kinetic energy is increasing and the potential energy is decreasing.

However, the total amount of these two forms of energy is remaining constant. Whatever potential energy is lost in going from position A to position D appears as kinetic energy. There is a transformation of potential energy into kinetic energy as the bob moves from position A to position D. Yet the total mechanical energy remains constant.

We would say that mechanical energy is conserved. As the bob moves past position D towards position G, the opposite is observed. Kinetic energy decreases as the bob moves rightward and more importantly upward toward position G.

There is an increase in potential energy to accompany this decrease in kinetic energy. Energy is being transformed from kinetic form into potential form. Yet, as illustrated by the TME bar, the total amount of mechanical energy is conserved. This very principle of energy conservation was explained in the Energy chapter of The Physics Classroom Tutorial.

Our final discussion will pertain to the period of the pendulum. As discussed previously in this lesson , the period is the time it takes for a vibrating object to complete its cycle. In the case of pendulum, it is the time for the pendulum to start at one extreme , travel to the opposite extreme , and then return to the original location.

Here we will be interested in the question What variables affect the period of a pendulum? We will concern ourselves with possible variables. The variables are the mass of the pendulum bob, the length of the string on which it hangs, and the angular displacement. The angular displacement or arc angle is the angle that the string makes with the vertical when released from rest. These three variables and their effect on the period are easily studied and are often the focus of a physics lab in an introductory physics class.

The data table below provides representative data for such a study. In trials 1 through 5, the mass of the bob was systematically altered while keeping the other quantities constant. By so doing, the experimenters were able to investigate the possible effect of the mass upon the period. As can be seen in these five trials, alterations in mass have little effect upon the period of the pendulum.

In trials 4 and , the mass is held constant at 0. However, the length of the pendulum is varied. By so doing, the experimenters were able to investigate the possible effect of the length of the string upon the period. As can be seen in these five trials, alterations in length definitely have an effect upon the period of the pendulum. As the string is lengthened, the period of the pendulum is increased.

There is a direct relationship between the period and the length. Finally, the experimenters investigated the possible effect of the arc angle upon the period in trials 4 and The mass is held constant at 0. As can be seen from these five trials, alterations in the arc angle have little to no effect upon the period of the pendulum.

So the conclusion from such an experiment is that the one variable that effects the period of the pendulum is the length of the string. Increases in the length lead to increases in the period. But the investigation doesn't have to stop there. The quantitative equation relating these variables can be determined if the data is plotted and linear regression analysis is performed.

The two plots below represent such an analysis. In each plot, values of period the dependent variable are placed on the vertical axis. In the plot on the left, the length of the pendulum is placed on the horizontal axis. The shape of the curve indicates some sort of power relationship between period and length. The results of the regression analysis are shown. The analysis shows that there is a better fit of the data and the regression line for the graph on the right. As such, the plot on the right is the basis for the equation relating the period and the length.

For this data, the equation is. Using T as the symbol for period and L as the symbol for length, the equation can be rewritten as. The value of 2. A pendulum bob is pulled back to position A and released from rest. The bob swings through its usual circular arc and is caught at position C. Determine the position A, B, C or all the same where the …. The force of gravity is everywhere the same since it is not dependent upon the pendulum's position; it is always the product of mass and 9.

The restoring force is greatest at A; the further that the bob is from the rest position, the greater the restoring force. The speed is greatest at C. The restoring force accelerates the bob from position A to position C. By the time the bob reaches C, it has accelerated to its maximum speed. The potential energy is the greatest at A. The potential energy is the greatest at the highest position.

The kinetic energy is the greatest at position C; kinetic energy is greatest at the lowest position. By the time the bob reaches C, all the original potential energy has been transformed into kinetic energy.

The total mechanical energy is everywhere the same since energy is conserved by a pendulum. Answer: Energy is conserved. A pair of trapeze performers at the circus is swinging from ropes attached to a large elevated platform.

Suppose that the performers can be treated as a simple pendulum with a length of 16 m. Determine the period for one complete back and forth cycle. Pendulum A: A g mass attached to a 1.

The mass of the bob is not an important variable; only the length of the string will effect the period and thus the frequency. Frequency and period are inversely related. The pendulum with the smallest period will have the highest frequency of vibration. A longer pendulum has a higher period; a shorter pendulum will have a smaller period.

Thus, the pendulum with the shorter string will have a higher frequency of vibration. Anna Litical wishes to make a simple pendulum that serves as a timing device. She plans to make it such that its period is 1. What length must the pendulum have? The length comes out to be 0.

### The vertical pendulum

Figure 1. The horses on this merry-go-round exhibit uniform circular motion. Figure 2. There is an easy way to produce simple harmonic motion by using uniform circular motion. A ball is attached to a uniformly rotating vertical turntable, and its shadow is projected on the floor as shown.

The shadow undergoes simple harmonic motion. So observing the projection of uniform circular motion, as in Figure 2, is often easier than observing a precise large-scale simple harmonic oscillator. If studied in sufficient depth, simple harmonic motion produced in this manner can give considerable insight into many aspects of oscillations and waves and is very useful mathematically. In our brief treatment, we shall indicate some of the major features of this relationship and how they might be useful.

The point P is analogous to an object on the merry-go-round. The projection of the position of P onto a fixed axis undergoes simple harmonic motion and is analogous to the shadow of the object. At the time shown in the figure, the projection has position x and moves to the left with velocity v. Its projection on the x-axis undergoes simple harmonic motion. Note that these velocities form a similar triangle to the displacement triangle.

To see that the projection undergoes simple harmonic motion, note that its position x is given by. Figure 4. The position of the projection of uniform circular motion performs simple harmonic motion, as this wavelike graph of x versus t indicates. This expression is the same one we had for the position of a simple harmonic oscillator in Simple Harmonic Motion: A Special Periodic Motion. If we make a graph of position versus time as in Figure 4, we see again the wavelike character typical of simple harmonic motion of the projection of uniform circular motion onto the x -axis.

Now let us use Figure 3 to do some further analysis of uniform circular motion as it relates to simple harmonic motion. Taking ratios of similar sides, we see that.

This expression for the speed of a simple harmonic oscillator is exactly the same as the equation obtained from conservation of energy considerations in Energy and the Simple Harmonic Oscillator.

You can begin to see that it is possible to get all of the characteristics of simple harmonic motion from an analysis of the projection of uniform circular motion. Finally, let us consider the period T of the motion of the projection. This period is the time it takes the point P to complete one revolution.

Thus, the period T is. Thus, the period of the motion is the same as for a simple harmonic oscillator. We have determined the period for any simple harmonic oscillator using the relationship between uniform circular motion and simple harmonic motion.

Some modules occasionally refer to the connection between uniform circular motion and simple harmonic motion. Moreover, if you carry your study of physics and its applications to greater depths, you will find this relationship useful. It can, for example, help to analyze how waves add when they are superimposed. Identify an object that undergoes uniform circular motion.

Describe how you could trace the simple harmonic motion of this object as a wave. A record player undergoes uniform circular motion. You could attach dowel rod to one point on the outside edge of the turntable and attach a pen to the other end of the dowel. As the record player turns, the pen will move. You can drag a long piece of paper under the pen, capturing its motion as a wave. Skip to main content. Oscillatory Motion and Waves. Search for:. Uniform Circular Motion and Simple Harmonic Motion Learning Objectives By the end of this section, you will be able to: Compare simple harmonic motion with uniform circular motion.

Figure 3. A point moving on a circular path. Check Your Understanding Identify an object that undergoes uniform circular motion. Solution A record player undergoes uniform circular motion. A novelty clock has a 0. What is the maximum velocity of the object if the object bounces 3. At what positions is the speed of a simple harmonic oscillator half its maximum?

A ladybug sits What is the maximum velocity of its shadow on the wall behind the turntable, if illuminated parallel to the record by the parallel rays of the setting Sun? Licenses and Attributions. CC licensed content, Shared previously.

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