Physics 105, Fall Term, 2009
Did you complete the reading assignment?
1) The direction of
torque is either clockwise or counterclockwise
2) Rotational equilibrium occurs when
torques are balanced
http://www.ngsir.netfirms.com/englishhtm/Torque.htm. The controls
can be a little strange at first. Look at the quick explanations below the
applet for how to use the controls. The most helpful view is the view that
shows the numbers rather than the pictures. It is often easier to to adjust
the position of the pivot point that it is to change the position of the
mass or spring scale. Click the box labeled 'Spring balance vertical, beam
horizontal'; this will force the beam to be in equilibrium in a horizontal
position and will change the force on the spring scale to make it physically
possible to be in rotational equilibrium.
Move the pivot point back and forth between the mass and spring scale while
observing the changes in the spring scale. Is the force applied by the
spring scale always the same as the force of gravity acting on the mass?
What happens to the force applied by the spring scale when the pivot point
is moved closer to the mass?
Force stays the same
What happens to the force applied by the spring scale when the force of
gravity acting on the mass is increased?
Two weights of equal mass are placed on opposite sides of a pivot point on a
beam. What must be true about the distances of the masses from the pivot point
for the beam to be in rotational equilibrium?
The masses must be equal distances from the pivot point.
To keep the beam in rotational equilibrium, would the direction of the
torque of the spring scale need to change if the spring scale was put on the
same side of the pivot point as the mass? Why or why not?
No, the direction of the torque caused by the spring scale would still need to be in a clockwise direction.
To keep the beam in rotational equilibrium, would the direction of the force
of the spring scale need to change if the spring scale was put on the same
side of the pivot point as the mass? Why or why not?
Yes, the direction of the force of the sprig scale would need to be up rather than down. This would allow the direction of the torque caused by the spring scale to remain in a clockwise direction and allow rotational equilibrium to still exist.
The comments entered in these last two boxes go into a big anonymous data file that I will use to guide the lectures of the day. That means two things:
1) If you have a specific question or concern and would like an individual
answer you will need to come by the office or send an email.
2) If you really want to get an anonymous comment to me before the lecture, it
must be submitted before 11am that day.
Was there anything that you didn't understand in the reading assignment?
What was confusing to you?