cahier physique - physics workbook

PURPOSE: The weight of an object is the amount of force that gravity exerts on the mass of the object. When an object is weighted on a spring scale, the pull of gravity on the object caused the spring scale to stretch. A relationship exists between the amount of stretch (or elongation of the spring) that the object produces and the amount of gravitational force pulling on the object. In this lab you will investigate the relationship that exists between the weight of an object and the stretch (elongation of a spring ).(called Hooke's law).

DISCUSSION: When a force is applied, an object may be stetched, compressed, bent, or twisted. The electrical forces between atoms in the object resist these changes. When the applied force is removes, the electrical forces return the objects to its original shape. Too large an applied force may overcome these resisting forces and cause the object to permanently deforms.

PROCEDURE:
STEP1: Attache the spring to the top of the stand.

STEP2: Attache the mass holder to the free end of the spring. Note carefully the position of the botton of the mass holder. The spring is at rest. Place a piece of masking tape to mark the position. This position will be your origin (0 stretch). Note the mass of the mass holder: _________________________

STEP3: Attach different masses to the holder. 100g, 200g, 250g, 300g, 350g, 400g ....) and each time record the strain the TABLE A. The strain in each case is the difference between the final position of the load and your origin.
GIVE THE TEACHER A BREAK: DO NOT PLAY WITH THE SPRING AND DO NOT OVER STRETCH IT.

TRIAL	1	2	3	4	5	6	7	8
MASS (g) = mass of holder + load	100g	200g
MASS (kg) = MASS (g)/ 1000
WEIGHT (N) = MASS(kg) x 10 m/s/s
STRETCH (cm)

STEP 3: FIll the TABLE.

ANALYSIS:
1) Make a graph weight vs stretch. weight is along the y-axis and stretch is along the x-axis. DO NOT CONNECT THE DOTS. Find the best fit line. Don't forget to label the axis and to title the graph. You can use your TI to find the regression line.

2) What kind of relationship exists between the weight and the stretch (elongation):
The stretch is ________________ to the weight.

3) Compute the slope ___________ . Units are N/cm. convert the slope to N/m.

4) Can you find the equation of the line ? y = ____ x

5) You just have demonstrated Hooke's law: ____________________

6) What is the spring's constant ? spring 's constant = _______________. (slope)/

7) Can you state Hooke's law in words ? _______________________________________________

GOING FURTHER:

8) In an experiment, a student varied the force applied to a spring and measured the resulting elongation. The table shhows the average elongation for three trials with each force.

Force (N)	Average Elongation (m)
0.00	0.000
1.00	0.040
2.00	0.075
3.00	0.120
4.00	0.165
5.00	0.200

A) Using the data in the table graph Force vs Elongation. Force along the y-axis and elongation along the x-axis. Don't forget to label the axis and to give a title to the graph.
Along the x-axis : 1 square = 0.001 m along the y-axis : 2 squares = 1.00 N

B) Draw the line of best fit. Use your line to determine the spring constant.