Docsity
Log inSign up
Docsity
Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity

Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan

Guidelines and tips
Guidelines and tips
Sell on Docsity
Sell on Docsity
Log inSign up

Prepare for your exams

Study with the several resources on Docsity

Find documents

Prepare for your exams with the study notes shared by other students like you on Docsity

Search Store documents

The best documents sold by students who completed their studies

Search through all study resources
Docsity AINEW

Summarize your documents, ask them questions, convert them into quizzes and concept maps

Explore questions

Clear up your doubts by reading the answers to questions asked by your fellow students

Earn points to download

Earn points by helping other students or get them with a premium plan

Share documents
download point icon20 Points

For each uploaded document

Answer questions
download point icon5 Points

For each given answer (max 1 per day)

All the ways to get free points
Get points immediately

Choose a premium plan with all the points you need

Study Opportunities

Choose your next study program

Get in touch with the best universities in the world. Search through thousands of universities and official partners

Community

Ask the community

Ask the community for help and clear up your study doubts

University Rankings

Discover the best universities in your country according to Docsity users

Free resources

Our save-the-student-ebooks!

Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors

From our blog

Exams and Study
Go to the blog

Rotational Motion at The Playground - Laboratory 5 | PHYS 101, Lab Reports of Physics

University of Oregon (UO)Physics

Material Type: Lab; Class: Essentials of Physics >3; Subject: Physics; University: University of Oregon; Term: Unknown 1989;

Typology: Lab Reports

Pre 2010

Uploaded on 07/23/2009

koofers-user-2am-1
koofers-user-2am-1 🇺🇸

10 documents

1 / 12

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
NAME____________________________________ DATE________________
Materials by Dean Livelybrooks — dlivelyb@hendrix.uoregon.edu 1
Lab 5: Rotational motion at the playground
Essentials of Physics: PHYS 101
Important note: this lab meets at the playground located at the SW corner of 23rd and
University streets, about 7 blocks south of the UO campus.
Many of the fun things to do at a playground involve rotational motion— moving in circles.
This lab comprises four experiments: the barbell, the teeter-totter; the swing; and the merry-go-
round. You will be undertaking all three experiments.
Experiment: Teeter totter tallies total torques! Story at ten
Introduction:
You’re sitting on one end of a teeter totter, minding your own business, when the big class bully
comes along and plops down on the other end, sending you flying. You swear to seek revenge
via the laws of physics. What can you do next time?
Question: Given that the class bully weighs twice as much as you, how can you change how you
sit on the teeter totter so that you both balance when he sits on the other end? Be specific and
explain your reasoning. Draw diagrams that illustrate your method.
Procedures:
1. Have the heaviest and lightest members of your group sit on either end of a teeter-
totter.
2. Make adjustments until the two group members balance.
pf3
pf4
pf5
pf8
pf9
pfa

Partial preview of the text

Download Rotational Motion at The Playground - Laboratory 5 | PHYS 101 and more Lab Reports Physics in PDF only on Docsity!

NAME____________________________________ DATE________________

Materials by Dean Livelybrooks — dlivelyb@hendrix.uoregon.edu 1

Lab 5: Rotational motion at the playground

Essentials of Physics: PHYS 101

Important note: this lab meets at the playground located at the SW corner of 23rd^ and University streets, about 7 blocks south of the UO campus. Many of the fun things to do at a playground involve rotational motion— moving in circles. This lab comprises four experiments: the barbell, the teeter-totter; the swing; and the merry-go- round. You will be undertaking all three experiments. Experiment: Teeter totter tallies total torques! Story at ten Introduction: You’re sitting on one end of a teeter totter, minding your own business, when the big class bully comes along and plops down on the other end, sending you flying. You swear to seek revenge via the laws of physics. What can you do next time? Question : Given that the class bully weighs twice as much as you, how can you change how you sit on the teeter totter so that you both balance when he sits on the other end? Be specific and explain your reasoning. Draw diagrams that illustrate your method. Procedures:

  1. Have the heaviest and lightest members of your group sit on either end of a teeter- totter.
  2. Make adjustments until the two group members balance.
  1. Have the third group member measure the distance from the pivot point of the teeter- totter to the center (center of gravity) of where each balanced group member is sitting. (This distance is called the lever arm .)
  2. Do two trials with the same two group members at the same ends of the teeter-totter. Now switch ends and do two more trials. Record your average lever arm distance for each balanced group member in the table below. Record the (approximate) weights of the two group members below. Observations for Part One: Data Table: Part One of Teeter Totter Experiment weight (lbs) force (N) Observations Lever arm (m) Torque (lever arm x force (N-m)) member 1 member 2 Calculations/Questions:
  3. Convert weights (in lbs) to force in Newtons (N) using the following formula:

______ (weight in lbs ) ⋅ 0.455 kg/lb ⋅ 9.8 m/s/s = ______ (weight in N)

Fill in the second column of the table above.

  1. Calculate the torques ((τ) lever arm x force) and fill in the appropriate column above. What affect did the changes you made (to balance the two group members) have on the torques they exert on the teeter-totter?
  2. What can you say about the sum of the torques exerted by the two group members on the teeter-totter? Again, draw diagrams to clarify your explanation.

displacement from equilibrium / length of swing = __________ (starting angle in radians) (note: 0.5 radians is a little less than 30 degrees and corresponds to a displacement that is half the length of the swing.) 7.Enter the torque on the swinger for each trial. To do so, use the following formula: weight of swinger x starting angle = __________ (return force) lever arm x return force (from just above) = ___________ (torque on swinger) Calculations/Questions:

  1. Which of the three characteristics above, when varied, had the greatest affect on the period of swinging? The moment of inertia, I, of a swing (simple pendulum) is proportional to its mass. If you halve the mass of someone on the swing, the swing’s moment of inertia will halve, making it easier to swing.
  2. If you double the mass of the swinger, how does its moment of inertia change? (be specific).

Data Table: Swing Experiment

Characteristic/variable being observed: Weight of swinger (N) Lever arm (m) Displace- ment from equil. (m) Starting angle (radians) Return force (n) Torque on swinger (N-m) Period for 5 swings (s) Period T (s) Characteristic/variable being observed: Weight of swinger (N) Lever arm (m) Displace- ment from equil. (m) Starting angle (radians) Return force (n) Torque on swinger (N-m) Period for 5 swings (s) Period T (s)

Characteristic/variable being observed: Weight of swinger (N) Lever arm (m) Displace- ment from equil. (m) Starting angle (radians) Return force (n) Torque on swinger (N-m) Period for 5 swings (s) Period T (s)

  1. If you double the mass of someone on a swing, how does the torque on it change? Again, be specific.
  2. How does the ratio of the torque to the moment of inertia (T/I) change when you double the mass of the swinger? This ratio, called the angular acceleration , determines how long it takes for the swinger to return to equilibrium from the starting position. Can you use this to explain your observations regarding how changing the mass of the swinger affected the period of swinging?
  3. To verify that changing the mass has no affect on the period of swinging, have the lightest and heaviest members of your group swing side by side. Is it relatively easy for the two swingers to “synchronize?” Why?
  1. Mark one point on the outside edge of the merry-go-round, directly along the line formed by the spring scale and the mass.
  2. Set the merry-go-round spinning so that it completes one full revolution in about 4 seconds. A second group member is responsible for timing the period (time) of a revolution.
  3. The person on the merry-go-round is responsible for reading the spring scale.
  4. The third member of the group is responsible for recording the revolution time and the spring scale reading, which are to be entered below.
  5. The entire procedure should be repeated, but with the 1kg mass+cart placed on cardboard near the outside edge of the merry-go-round (one can tape two pieces of cardboard to the merry-go-round at the two locations in advance) Again, measure the distance between the mass and the center of the merry-go-round, spin the latter at about one revolution per 4 seconds, and time the revolution and measure the force. Results should be recorded in the appropriate row, below. Observations: Data Table: Part Two of Merry-go-round Experiment Radius, r, (m) Period of revolution (s) Force on spring scale (N) Distance traveled (m) Speed, s, (m/s) 1/2 way out all-the-way out Questions/Calculations:
  6. In completing one revolution, the mass traveled a distance— the circumference of a circle centered on the merry-go-round— in some amount of time. The formula relating the distance around a circle (circumference) to the radial distance is:

2 ⋅ radial distance ⋅ 3.142 = _____________ circumference

Calculate the distances traveled by the mass at each position (1/2 way, all-the-way out) and fill in the “Distance traveled” column, above.

  1. Is the amount of time needed for the cart+mass to complete one revolution at 1/2-way different than at all-the-way out? (hint: think about how the segments of the merry-go-round move.) Is the distance traveled different?
  1. Calculate the average speed of the mass in both positions and record above (remember our definition for speed?). How much did the speed increase in moving from 1/2-way to all-the- way out?
  2. When the mass is moving at a constant speed around a circle, does its velocity change (remember, velocity is both speed and direction)? If the mass’s velocity does change, would it have an acceleration? Explain.
  3. Any mass undergoing an acceleration must be subject to a net force. The centripetal force, provided by the spring scale in this case, is what causes the 1kg mass to turn in a circle. This force depends both on the speed of and how far away the mass is from the center. The formula (which assumes the velocity acts perpendicular to the lever arm) is:

Fc = m · s · s / r

The radius doubled when we moved the mass from 1/2-way to all-the-way out. How did the

average speed increase?. Fc depends on the speed “squared” (s · s), but also on 1/r. Is this

definition for centripetal force consistent with your results?

  1. Two cars go through the same curve in the road on a rainy day. One is going slowly, and proceeds without problem. The other goes through the curve twice as fast and “spins out.” Explain why in terms of the information above. Part Two: May the force be with you Introduction: Playing on a merry-go-round is a sure fire way to get dizzy in a hurry. The motion of a kid spinning around on a merry-go-round is analogous to planets spinning around the sun. For the kid, friction between the kid’s feet (and hands if they’re holding on) provide a force that keeps them moving in a circle. The attraction of gravity between the sun and a planet keep it in its orbit. Question: What would happen if your feet slipped while you were spinning around? Would you fly off away from the center of the merry-go-round? Would you continue in a straight line? Would you fall towards the center? Make a prediction and state your reasoning below:

Part Three: How high the moon? Introduction: Did you know that the moon is moving slowly away from the Earth? Each time we have another full moon, it has moved about 1/4 centimeters further away from the Earth. What is causing this? One explanation is that the Earth’s rotation is slowing down and conservation of angular momentum dictates that the moon move further away to compensate. To understand this explanation, it is useful to know what the term “conservation of angular momentum” means. That is the purpose of this part of the merry-go-round experiment. Procedures:

  1. Tie a piece of bright flagging on one handle of the merry-go-round.
  2. One group member should stand on the merry-go-round at the outside edge, facing inwards.
  3. Another person is the timer, responsible for timing how long the merry-go-round and person take to complete one revolution.
  4. Start the merry-go-round spinning rapidly. Immediately time the period of revolution of the merry-go-round and record it, below.
  5. As soon as the period is timed, the person on the merry-go-round should begin walking towards the center. The third group member should observe what happens to the speed of the outer edge of the merry-go-round as this happens and record it below.
  6. The person on the merry-go-round should stop walking when they reach 1/2-way in. The timer should then determine the period of revolution and record it below.
  7. Repeat this for 3 trials, and record the results of each trial below. Observations: Data Table: Part Three of Merry-go-round Experiment period at 1/2-way point (s) period at outer point (s) observations trial 1 trial 2 trial 3 average Questions:
  1. Calculate the average periods for 1/2 way and all-the-way out from the columns above. Enter in the table.
  2. What happened to the period of revolution when the person walked towards the center?
  3. Angular momentum depends both on the moment of inertia (distance away from the center) and the speed at which the person is spinning. In this experiment, the radius decreased as the person walked towards the center. Did the speed decrease, stay the same, or increase? How do you know this?
  4. If the angular momentum is to be “conserved,” it won’t change as the person walks towards the center. Yet the distance from the center has decreased in doing so. What must happen to the person’s speed, then, if angular momentum is to be conserved? Did you observe this? Epilogue: The moon is spinning around the Earth and, thus, it has angular momentum relative to the Earth. The Earth is also spinning, but the forces of ocean tides are causing it to slow down. Thus its angular momentum is decreasing. To conserve total angular momentum, that of both the moon and Earth, the moon must move outwards to compensate. Interestingly, the moon is also what causes some of the tidal forces causing the Earth to slow down. Obviously this is all part of the moon’s grand plan to eventually escape the Earth! Definitions: Name Symbol Definition in words Formula Center of rotation Example, place where teeter-totter is suspended, place where swing is attached to crosspole. Lever arm r Distance from center of rotation Moment of Inertia I Resistance to change in rotation for dumbbell m • r • r Grav. force (Weight) Fg Force exerted on a mass (you) by another object (the Earth, usually).

F = m·g

Acceleration g The (constant) acceleration (9.8m/s/s) of any thing g = F / m (only