Download Experiments Involving Static Equilibrium

Experiments Involving Static Equilibrium
by SHS Encoder 3 on June 14, 2017
lesson duration of 0 minutes
under General Physics 1
generated on June 14, 2017 at 11:22 pm
Tags: Static Equilibrium, Experiments
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Generated: Jun 15,2017 07:22 AM
Experiments Involving Static Equilibrium
( 2 hours )
Written By: SHS Encoder 3 on July 8, 2016
Subjects: General Physics 1
Tags: Static Equilibrium, Experiments
Resources
University Physics with modern Physics (12th ed.)
Young, H. D., & Freedman, R. A. (2007). University Physics with modern Physics (12th ed.). Boston, MA: AddisonWesley.
Physics for scientists and engineers (5th ed.)
Tipler, P. A., &Mosca, G. (2008).Physics
(2008).Physics for scientists and engineers (5th ed.). New York: W. H. Freeman.
Content Standard
The learners demonstrate an understanding of...
1. Moment of inertia
2. Angular position, angular velocity, angular acceleration
3. Torque
4. Torque-angular acceleration relation
5. Static equilibrium
6. Rotational kinematics
7. Work done by a torque
8. Rotational kinetic energy
9. Angular momentum
10. Static equilibrium experiments
11. Rotational motion problems
Performance Standard
The learners are able to Solve multi-concept, rich context problems using concepts from rotational motion, fluids,
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oscillations, gravity, and thermodynamics
Learning Competencies
The learners determine whether a system is in static equilibrium or not
The learners perform an experiment involving static equilibrium and analyze the data—identifying discrepancies
between theoretical expectations and experimental results when appropriate
INTRODUCTION
20 mins
1. Discuss the conditions for which a rigid object is in static equilibrium:
Do a quick review on Newton’s First Law of Motion.
Discuss the rotational analog of Newton’s First Law of Motion, that is,
is, when the net torque caused by external
forces acting on a rigid object is zero, then the angular velocity is constant.
Tell the learners that, hence, for a rigid object to remain at rest (i.e., static equilibrium), the following
conditions should be satisfied:
2. Provide examples or show using simple diagrams wherein the net force and the net torque are nonzero and zero,
respectively, and vice versa.
3. Concept check: ask the learners the following:
Which situation satisfies both conditions for equilibrium?
i. A seagull gliding at a constant angle below the horizontal and at a constant speed.
ii. An automobile crankshaft turning at an increasing angular speed in the engine of a parked car.
iii. A thrown baseball that does not rotate as it sails through the air.
Does a rigid object in uniform rotation about a fixed axis satisfy the first and second conditions for
equilibrium? Explain.
INSTRUCTION
70 mins
1. Remind the learners that they are only required to submit one output per group at the end of the session.
2. Distribute the laboratory activity guide (refer to the Appendix).
3. Instruct the learners to read the procedures carefully.
4. Have the learners perform the laboratory activity.
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5. Questions, enquiries, clarifications, and further explanations regarding the laboratory activity may be entertained
during the course of their experiment.
6. The learners should sought after a percentage error of less than or equal to 10%.
EVALUATION
10 mins
1. Wrap up the activity by asking the following questions
a. Draw the free-body diagram of the meterstick for Activities A, B, C, D, and E. Prior to activities B onward, why is it
that the point of balance is just the location of the center of mass of the meterstick? Justify your answer using your
fbd.
b. For Activities B, C, and D, explain why you do not have to account for the mass of the meterstick when the clamp is
placed at the center in formulating the equations of motion.
c. Enumerate possible sources of error for all activities.
d. Give examples for a system acted on by a nonzero net force and a zero net torque.
e. Consequently, give examples for a system acted on by a nonzero net torque and a zero net force.
ENRICHMENT
20 mins
1. Write the following problems on the board and have the learners answer each item.
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a. A uniform sphere of mass m = 0.85 kg and radius r = 4.2 cm is held in place by a massless rope attached to a
frictionless wall a distance L = 8 cm above the center of the sphere. Find (a) the tension on the rope and (b) the force
on the sphere from the wall.
b. Figure at the left shows the anatomical structures in the lower leg and foot that are involved in standing on tiptoe,
with the heel raised slightly off the floor so that the foot effectively contacts the floor only at Point P. Assume distance a
= 5 cm, distance b = 15 cm, and the person’s weight is 900 N. Of the forces acting on the foot, what are the (a)
magnitude and (b) direction of the force at Point i from the calf muscle and the (c) magnitude and (d) direction of the
force at Point B from the lower leg bones? (Hint: Point B is the pivot point).
APPENDIX:
APPENDIX: Laboratory Activity Guide
Group number: _________
Group members: _____________________________________________________________
Date: _________
Static equilibrium
Objective: This session covers six activities to apply the conditions of static equilibrium (zero net force and zero net
torque with the body initially at rest) on a homogeneous body exerted by a number of forces.
Materials:
Pivot clamp (one piece)
Meterstick (one piece)
Objects with 100-g, 200-g, and 500-g masses (one each)
Object of unknown mass (one piece)
Stand (one piece)
Activity A: Balancing the meterstick by locating its center of mass
1. The meterstick can be considered homogenous. Hence, in theory, the center of mass of the meterstick is its
geometric center.
center.
2. Position the pivot clamp at the meterstick’s 0.5-m mark such that the meterstick suspends on it in equilibrium.
3. This point of balance is the center of mass of the meterstick. Record this value.
4. Determine the extent for which the meterstick balances by moving the pivot clamp. These end points determine the
uncertainty in the center of mass. Again, record these values.
Note: For Activities B, C, and D make sure that that the pivot clamp is still situated at the 0.5-m mark.
Activity B: Balancing the meterstick using two masses.
1. Hang the 100-g mass at the 0.8-m mark of the meterstick.
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2. Hang the 200-g mass at the point by which the meterstick is still in equilibrium. Record this point
3. Find the theoretical value, that is, solve analytically the position of the 200-g mass in order to balance the meterstick
using the conditions for static equilibrium.
4. Calculate the percentage error.
Activity C: Balancing the meterstick using three masses
1. Hang the 100-g and the 200-g masses at the 0.1-m and at the 0.25-m mark, respectively.
2. Use the 500-g mass to balance the system. Record this point.
3. Again, solve the theoretical value using the conditions for static equilibrium.
4. Calculate the percentage error.
Activity D: Constructing a single-beam balance
1. Place the 500-g mass at the 0.4-m mark.
2. Use the object of unknown mass to balance the meterstick.
3. Knowing the position of this object that keeps the meterstick in equilibrium, determine the mass of this object.
4. Measure the mass of this object using a triple-beam balance.
5. Calculate the percentage error.
Activity E: Determining the mass of the meterstick using torque relations
1. Retain the position of the 500-g mass at the 0.3-m mark.
2. Balance the system by sliding the meterstick along the pivot clamp.
3. Notice that the meterstick has been sectioned into two regions by the pivot clamp with masses of each region
concentrated halfway between the edge of the meterstick and the tip of the clamp. See figure below:
4. Formulate the equation of the total torque on the system and then calculate the mass of the meterstick.
5. Weigh the meterstick and validate your experimental result by calculating the percentage error relative to the direct
measurement.
Download Teaching Guide Book 0 mins
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