Download Hooke`s Law Lab

Hooke’s Law PhET Lab
Purpose: To investigate Hooke's Law (The relation between force and stretch for a spring) F = -kx
and to review Newton's 3rd Law of Motion.
Discussion:
Theory: The shape of a body will distort when a force is applied to it. Bodies which are “elastic” distort
by compression or tension, and return to their original, or equilibrium, position when the distorting force is
removed (unless the distorting force exceeds the elastic limit of the material). Hooke's Law states that if the
distortion of an elastic body is not too large, the force tending to restore the body to equilibrium is proportional
to the displacement of the body from equilibrium. Stated mathematically:
F =-kx
Where F is the restoring force, k is a constant of proportionality and x is the distance the object has been
displaced from its equilibrium position. The minus sign signifies that the restoring force acts in the opposite
direction to the displacement of the body from the equilibrium position.
If a body, which obeys Hooke’s Law, is displaced from equilibrium and released, the body will undergo
“simple harmonic motion”. Many systems, such as water waves, sound waves, ac circuits and atoms in a
molecule, exhibit this type of motion
When you apply a force to a spring or a rubber band, it stretches. A scientist might ask, "How is the
force that you apply related to the amount of stretch?" This question was answered by Robert Hooke, a
contemporary of Newton, and the answer has come to be called Hooke's Law.
Hooke's Law is a very important and widely-used law in physics and engineering, with applications that
go far beyond springs and rubber bands.
You can investigate Hooke's Law by measuring the quantity of known forces that stretch a spring a
measurable distance without distorting the spring. A convenient way to apply a precisely-known force is to let
the weight of a known mass be the force used to stretch the spring. The force can be calculated from Fw = mg.
The stretch of the spring can be measured by noting the position of the end of the spring before and during the
application of the force.
1.
What is Hooke’s law? Read from the information above and physicsClassroom.com prior to answeringanswer in your lab notebook.
Equipment:
PhET Simulation “Masses and Springs” from http://phet.colorado.edu/en/simulations/category/physics
Procedure:
1. Go to PhET webaddress and run Masses and
Springs.
2. Construct a data table in lab book. You will need to record magnitude of hanging mass and displacement
of spring (position of the end of the spring before and after the mass is added).
3. Use each labeled mass provided (50 g, 100 g, and 250 g)
4. Calculate the force applied to the spring. Perform three trials using Spring #3 - farthest to the right),
set to the default setting for stiffness of the spring. Place a mass on the spring and record data.
5. For each trial, record mass, starting position of the spring (before hanging the mass) and ending position
of the spring (while it is being stretched – the ruler on the screen is movable- click and drag ) and
record the change in position as displacement.
6. Repeat the process using spring #3 but set the stiffness to hard.
Calculations:
1. Calculate the force applied to the springs in each trial, u se g = 9.8 m/s2.
2. Draw graphs of force versus stretch for the spring at default and the spring set to hard. What is the
slope of each line on graph?
Use a minimum of two of the following sources:
http://www.4physics.com/phy_demo/HookesLaw/HookesLawLab.htm
http://webphysics.davidson.edu/applets/animator4/demo_hook.html
http://www.matter.org.uk/schools/content/hookeslaw/index.html
http://www.physicsclassroom.com/
as you answer the questions. Cite the sources within the paper (in-text or parenthetical) using APA format
(http://owl.english.purdue.edu/owl/resource/560/03/ OR http://www.apastyle.org/learn/quick-guide-onreferences.aspx#In-Text ) Be sure to write references (APA format) for each source and include at the end of
the conclusion. Submit answers along with references on TurnItIn.
Questions:
1. Imaging hanging an object (at rest) from a spring scale. Draw a FBDs to show all forces that act:
A. on the object
B. on the clamp (the hook of the spring scale)
2. What is the net force on:
A. the object?
B. the clamp?
3. Are the forces that act on the object equal and opposite? Are they a Newton's Third Law force pair?
Explain.
4. Are the forces that act on the clamp equal and opposite? Are they a Newton's Third Law force pair?
Explain.
5. What is the relationship of the force on the spring and the stretch of the spring?
6. What does the slope of the graph represent?
7. What is a real-world application of Hooke’s Law?
8. At which point(s) does the mass on a vibrating spring have the (draw diagrams and use vectors for F, a,
and v).
a. greatest acceleration?
b. least acceleration?
c. largest force exerted on it?
d. smallest force exerted on it?
e. greatest velocity?
f. least velocity?
9. If the amplitude of the vibration for a spring is doubled, what happens to the period?
10. If the spring constant was 4 times as great, how would frequency and period be affected?