LAB 6 Hooke's Law

PhysicsLab6 June 14, 2010 Name __________________
Dr Dave Menke, Instructor

I Title: Hooke’s Law

II Purpose: To test Hooke’s law with gravity

Theory: Robert Hooke studied the forces on, and in, springs, back in the early 1600's. There are primarily two types of springs: one-dimensional and two-dimensional. The one-dimensional spring is fully compressed and cannot be compressed any further; however, it can be stretched. A two-dimensional spring is permanently partly stretched, so there are spaces between the coils. A two-dimensional spring may be compressed or stretched, such as an automobile’s shock absorbers. Hooke’s law states that the force on (or of) a spring is directly related to its displacement (either inward or outward). The relationship is:
F = - kx

where F is force, x is distance moved, and k is the spring constant, sometimes called force constant of the spring. Notice that there is a minus, or negative, sign in front of the k. This means that when you pull a spring, it “pulls back” opposite to your force. If you compress a spring, it pushes out, opposite to your force. Also note that x is for the x-direction. Since you will do this experiment vertically, in the y-direction, the relationship will be:
F = - ky

In this vertical set up, the spring force will equal the force of gravity:

F = mg = - ky

III Equipment List:
1. Spring Scale
2. Weights
3. Metric Ruler

IV Experimental Procedure:
1. Determine if your spring is a one-dimensional spring or a two-dimensional spring and record this data.
2. Zero out your tiny spring scale (Hooke’s law device) by determining its relaxed zero point.
3. Locate a small weight and determine its mass in grams. Convert the data from grams to kilograms and record this data.
4. Hang the small weight on the small spring.
5. Measure the downward displacement (how far down it moved from the zero) in centimeters. Convert the centimeters to meters and record this data.
6. Determine all forces and use the mks system.
7. Determine the spring constant from Hooke’s law, stated above.
8. Record the “true” spring constant that is given by the Professor

V Data & Calculations: (The Data will correspond to the numbers that require data from above)
1. Dimension of Spring :______________

2. Weight’s mass: _______________g = _____________ kg

3. Downward displacement:_______________cm = ________ m

4. Spring constant from Hooke’s law:_________________ N/m

5. “True” spring constant from the Professor: ____________

VI Results:
The purpose if this laboratory (test Hooke’s law with gravity) was / was not achieved due to:
F = - k y
VII Error Analysis:
A. Quantitative Error:

[|(True value) - (Your Value)| / (True value)] X 100% = Percent Error

B. Qualitative Error:
1. Personal -
2. Random -
3. Systematic –

VIII Questions:
1. Is there a difference doing this experiment vertically with gravity compared to horizontally where gravity is irrelevant?
2. What happens when you compress (push-in) the spring? If it is one-dimensional put N/A.
3. What happens when you stretch (pull out) the spring?
4. Which type of spring is best for this lab, and why?
5. Determine the constant of a spring that would be able to support a person of mass 100.0 kilograms. Let y = 1.0 m