PURPOSE:
To expose the student to new equipment and lab procedures. And to observe the relationship between angle of force and torque.

INTRODUCTION:
In physics, torque (or often called a moment) can informally be thought of as "rotational force" or "angular force" which causes a change in rotational motion. A metal hanger and meter stick will be acted upon by gravity to create a force. The meter stick is attached to a vertical rod at its left end (see picture below) and pivots from that attachment. A metal weight hangs from that meter stick. The Force based on the meter stick can be calculated using the equation:

F = m x g

where m = mass of the meter stick, and g = 9.8 m/s². The torque that this meter stick creates can be calculated using the equation:

Torque_meter = 1/2r x F x sin(angle)

where r = the lever arm length(1 meter), sin(90)=1[since gravity is acting perpendicularly] and Force as calculated above. Notice that since the meter stick is attached at one end to the vertical rod, only 1/2 of the radius is used.

The force due to the metal weight = m x g x sin(angle) also [once again gravity is perpendicular]. The torque produced by the metal weight can be calculated by :

Torque_weight = r x F

where r = the lever arm length(distance from the pivot point to where the weight hangs from the meter stick) and Force as calculated above. The total torque is thus:

Torque_total = Torque_weight + Torque_meter

In the picture a Newton spring scale holds the meter stick with weight in a horizontal position. As it hangs, the Force it shows is:

F = Torque_total / [r x sin(angle)]

where r = the lever arm length(distance from the pivot point to where the scale attaches to the meter stick), and the angle refers to the angle the scale makes in relation to the horizontal meter stick. During this lab you will adjust the angle and lever arm lengths and observe the results.

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The lab will be conducted on a meter stick with its left end attached to a support rod. The stick can pivot around this point. From the stick a metal weight is hung and the meter stick is supported from above by a Newton spring scale.

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If you get into trouble and perform some procedure that causes the lab to fail(lab equipment will no longer operate), you can press the "Reset" button and the simulation will return to the starting position.

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PROCEDURE:

1) You can adjust the background shading by clicking on the "Special" button to the right and selecting "Background". Click on the "Special" button and select "Print Blank Report" to obtain a web page that can be printed and used as a lab report. (the program will not be interrupted)

Phase 1: moving hanging mass position

2) Record the mass(in kg) of the meter stick as shown on the screen. Pick up the gray metal weight and place it on the electronic balance. Record its mass. Place the weight on the meter stick. Move the weight so that it hangs on the 0.90 meter mark on the meter stick. Move the blue Newton spring scale(grab the body) so it is also on this same mark. If you have changed the angle of the spring scale, set it back to 90 degrees. Record the force shown on the spring scale. Leave the spring scale in place and move the weight to the 0.80 m mark and record the force. Repeat this for a 0.70 m, 0.60 m and 0.50 m setting recording the force for each.

Phase 2: changing scale angle

3) Set the hanging mass on 0.90 m again, slide the scale to the 0.90 meter mark also. Record the force (it should match that first recorded above). Grab the protractor and set the bottom edge just in line with the top of the meter stick. Place the red dot (lower right corner of the protractor) on the point where the scale connects with the meter stick. Your protractor angle should read 90 degrees. Grab the top hook of the scale and slowly move it to the left. The scale should now start to angle down to the left. Adjust the angle until it reads 80 degrees on the protractor. Record the force. Record the force, without shifting the position of the weight or scale, at 70, 60 and 50 degrees.

Phase 3: moving scale position

4) Set the hanging mass on 0.90 m, slide the scale to the 0.90 meter mark and adjust the angle of the scale back to 90 degrees. Record the force (look familiar). Slide the scale to the 0.80 m mark and record the force(keep the scale at 90 degrees). Record the force when the scale is on the 0.80, 0.70, 0.60 and 0.50 m mark.

5) Calculate the requested values asked for on the lab sheet and any given by your teacher. For help on these values click on the "Special" button and select "View Data & Hints". Select "File Report" to send a copy to be viewed by your teacher.