cahier physique - physics workbook

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INTRODUCTION: Fill the blanks
bank: gravity - force - relationship - stretch -

weight of an object is the amount of_______ that gravity exerts on the mass of the object. When an object is weighted on a spring scale, the pull of __________ on the object causes the spring scale to __________. A relationship exists between the amount of _______ (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____________ 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 stretched, compressed, bent, or twisted. The electrical forces between atoms in the object resist these changes. When the applied force is removed, the electrical forces return the objects to its original shape.

PROCEDURE:

STEP1: Attach the spring to the top of the stand.

STEP2: Attach the mass holder to the free end of the spring. Note carefully the position of the bottom 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).

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. (that is your extension).
GIVE THE TEACHER A BREAK: DO NOT PLAY WITH THE SPRING AND DO NOT OVER STRETCH IT.
DO NOT USE IS AS A SLING SHOT. (that will mean a 0%)

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 weight is ________________ to the stretch (or elongation)..

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

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

5) To find the spring constant K, convert your slope (N/cm) to (N/m) K = _____________.

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

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 shows the average elongation for three trials with each force.

y = Force (N)	x = 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 = 0.01 along the y-axis : 2 squares = 1.00 N
you can use your TI.

B) Draw the line of best fit. Find the slope of the line. slope = ___N/m

C) find the spring constant. K = _____ N/m

2) A spring has a spring constant of 25 newtons per meter (K). Determine the magnitude of the minimum force required to stretch the spring 0.25meter from its equilibrium position.
hint: use F = K x

3) The graph below shows the relationship between the elongation of the spring and the force applied to the spring causing it to stretch.

What is the spring constant for this spring ? (it is a tricky question !!!)

hint: F = K X with X being the elongation and K the spring constant. So X = (1/K) F or elongation (y) = (1/K) x force (x)
to if you plot elongation vs force, the slope is _______ m/N but the spring constant K = ________ N/m.

4) When stretch or compressed, springs store potential energy, ready to be used. More stretched (or compressed) more energy the spring stores. The potential energy stored in such spring is Energy = 0.5 K x².
K(N/m) is the spring constant and x is the change in length (m). The unit for energy is joule.
A force of 0.2 newtons is needed to compress a spring a distance of 0.02 meter. THe potential energy stored in this spring is:
E = _____________ J.

5) A spring with a spring constant of 2 10² newtons per meter (the spring constant) is stretched 0.2 meter. How much potential energy is stored in the spring ?
E = ______________J.

6) Base your answer on the following graph, which represents the relationship between the force applied to a spring and its elongation.

A) Find the spring constant K (N/m)

B) How much energy the spring stores when the elongation is 0.4 m (use A))
hint: energy = 0.5 K x²

C) Use the graph to find how much force you need to exert to get an elongation of 0.35 m
Check your answer using the equation F = K x and solve for F.