PHY111 Online Lab #7 Uniform Circular Motion PDF

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PHY111, 161 ON-LINE LAB, Uniform Circular Motion

Lab #7 Uniform Circular Motion

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Download and save this document to your computer. Answer the questions directly on this document. When you are done, SAVE the file and return it to your TA via BB Learn. Please contact your TA with any questions or other issues. Introduction: In physics, circular motion is a movement of an object along the circumference of a circle or rotation along a circular path. This can be a planet in a circular orbit, a weight on a string swung overhead, or even a rotating wheel. It can be uniform, with constant angular rate of rotation and constant speed, or non-uniform with a changing rate of rotation. In this lab we will be discussing only Uniform Circular Motion. Task #1 Watch the following video in the link provided, it will go a long way in helping to explain the concepts we will be discussing: https://youtu.be/bpFK2VCRHUs

As we analyze the motion of objects in circles, there are three mathematical quantities that will be of primary interest to us. These three quantities are speed, acceleration. and force. The speed of an object moving in a circle is given by the following equation.

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PHY111, 161 ON-LINE LAB, Uniform Circular Motion

The acceleration of an object moving in a circle can be determined by either two of the following equations.

! The equation on the right (above) is derived from the equation on the left (above) by the simple substitution of the expression for speed. The net force (Fnet) acting upon an object moving in circular motion is directed inwards. While there may by more than one force acting upon the object, the vector sum of all of them should add up to the net force. In general, the inward force is larger than the outward force (if any) such that the outward force cancels and the unbalanced force is in the direction of the center of the circle. The net force is related to the acceleration of the object (as is always the case) and is thus given by the following three equations:

! Task #2 Now let’s do some basic calculations using what we’ve just learned. We are going to look at a very simplified version of the Earth-Sun system. Let’s assume that the orbit of the Earth around the Sun is basically circular (actually it is slightly elliptical, but for our purposes we will just say that it’s circular.) Here are a few other facts we will need as well: The Earth is approximately 150,000,000 kilometers (km) from the Sun. The time it takes for the Earth to travel around the Sun one time (it’s orbital Period) is of course one full year. But in physics we need to measure time in seconds. We define one year in Astronomy as 365.25 days which is equal to 31,557,600 seconds. 2

PHY111, 161 ON-LINE LAB, Uniform Circular Motion The mass of the Earth is 5.972 × 10 24 kg

Using the equations and information above answer the following questions (include units): 1. What is the distance that the Earth travels around the Sun in one full year? Be sure to convert your answer to meters (m). You may use scientific notation, for example: 9.9 x 10^10 m

2. What is the Average Speed of the Earth as it travels around the Sun? (m/s)

3. What is the angular Acceleration that Earth experiences as it travels around the Sun? (m/s2). In what direction does the acceleration vector point? 4. What is the net force (Fnet) acting on the Earth due to its circular motion around the Sun? (N) Which direction does the force vector point?

Task #3

Now, go to the following link: https://www.physicsclassroom.com/Physics-Interactives/Circular-and-Satellite-Motion/ Uniform-Circular-Motion/Uniform-Circular-Motion-Interactive 3

PHY111, 161 ON-LINE LAB, Uniform Circular Motion

In the simulation window that appears, click on the expansion icon in the upper left-hand corner. This will expand the simulation to full screen mode, making it easier to see. (When you are done using the simulation just use the escape key [Esc] on your keyboard to leave full screen mode). Take a moment to familiarize yourself with how the simulation works. You should toggle on both the velocity and acceleration vector buttons. You can start and pause the simulation with the button in the upper righthand corner. You can reset the simulation with the button in the upper left-hand corner.

Using the simulation, with both the velocity and the acceleration vector buttons toggled, answer the following questions. You may wish to reset the simulation for each set of questions. 1. Speed: What happens to the velocity vector when you increase the speed? What happens to the velocity vector when you decrease the speed? What happens to the acceleration vector when you increase the speed? What happens to the acceleration vector when you decrease the speed?

The velocity vector continues to point down and it gets larger as you increase the speed. when you decrease the speed the velocity factor decreases. The acceleration Factor increases when the speed increases and it also decreases when the speed decreases and the arrow points to the left at all times.

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PHY111, 161 ON-LINE LAB, Uniform Circular Motion

2. Radius: What happens to the velocity vector when you increase the radius? What happens to the velocity vector when you decrease the radius? What happens to the acceleration vector when you increase the radius? What happens to the acceleration vector when you decrease the radius?

The velocity vector does not change if you increase or decrease the radius. The acceleration vector does not change when the radius is increased but when the radius is decreased the velocity vector slowly increases and points to the left.

3. Mass: What happens to the velocity vector when you increase the Mass? What happens to the velocity vector when you decrease the Mass? What happens to the acceleration vector when you increase the Mass? What happens to the acceleration vector when you decrease the Mass?

Nothing happens to the velocity vector or the acceleration vector when mass is increased and decreased.

Task #4 Watch the following video: https://youtu.be/y2FmgoOht7Y 5

PHY111, 161 ON-LINE LAB, Uniform Circular Motion You may also want to re-watch the first video we fist viewed at the beginning one more time https://youtu.be/bpFK2VCRHUs

In your own words explain why the force and acceleration vectors in Uniform Circular Motion point inward. Also discuss the differences between Centripetal Force and Centrifugal Force.

The force and acceleration vectors in uniform circular motion point inward because they are always perpendicular of where the object is moving. And because it is moving in a circular motion the vectors continue to point towards the center. The difference between centripetal force and centrifugal force is that one says that forces are directed inward while the other says forces are pushing outward. Both videos suggested not to use centrifugal force because when objects are spinning in a circular motion the forces are pointing outward and using centripetal force.

PHY111, 161 ON-LINE LAB, Uniform Circular Motion

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