Torque

1
Torque

• A force causes a linear change in motion
  (acceleration).
• A torque causes a change in rotational motion
  (rotation).

2
TORQUE

• If you want to make a stationary object move,
  apply a force.
• If you want to make a stationary object rotate,
  apply a torque.

3
TORQUE

• Torque is a product of how much force is applied
  (FORCE) and how far from the axis of rotation
  that force is applied (LEVER ARM).
• Torque Force x Lever Arm

4
TORQUE

• Imagine a see-saw. If the two kids at each end
  are of different mass, explain how they can still
  keep the see-saw balanced.
• We know that the heavier kid needs to sit closer
  to the center of the see-saw. Why?

5
TORQUE

• Imagine a see-saw. If the two kids at each end
  are of different mass, explain how they can still
  keep the see-saw balanced.
• We know that the heavier kid needs to sit closer
  to the center of the see-saw. Why?
• In order for the see-saw to balance, there must
  be no rotation. This means that there cannot be
  any unbalanced torques acting on the see-saw.

6
TORQUE

• In order for the see-saw to balance, there must
  be no rotation. This means that there cannot be
  any unbalanced torques acting on the see-saw.

7
TORQUE

• In order for the see-saw to balance, there must
  be no rotation. This means that there cannot be
  any unbalanced torques acting on the see-saw.
• The heavier kid has more weight (force) so must
  have a smaller lever arm in order to make the
  product of force and lever arm (torque) equal
  that of the smaller kid sitting further from the
  axis.

8
TORQUE

• In order for the see-saw to balance, there must
  be no rotation. This means that there cannot be
  any unbalanced torques acting on the see-saw.
• The heavier kid has more weight (force) so must
  have a smaller lever arm in order to make the
  product of force and lever arm (torque) equal
  that of the smaller kid sitting further from the
  axis.
• When torques are balanced, there can be NO
  ROTATION

9
Stability

• Stand up
• Touch your toes
• No big deal right?

10
Stability

• Stand up
• Touch your toes
• No big deal right?
• Now, stand with your heels and butt in contact
  with a wall
• Try to touch your toes

11
Stability

• Stand up
• Touch your toes
• No big deal right?
• Now, stand with your heels and butt in contact
  with a wall
• Try to touch your toes
• Interesting that you CANNOT do it!

12
Stability

• Your center of gravity (any objects center of
  gravity) is that point in your mass that the
  earth pulls on. While it is true that the earth
  pulls on each and every part of your mass, we can
  mathematize your mass down to a single point.
  Yours happens to be somewhere in the vicinity of
  your belly button.

13
Stability

• What is interesting is that you can actually move
  your center of gravity (CG) outside of your body.
  If you change your shape (please see Figure 8.31
  on page 142), you can cause your CG to move
  forward.

14
Stability

• What is interesting is that you can actually move
  your center of gravity (CG) outside of your body.
  If you change your shape (please see Figure 8.31
  on page 142), you can cause your CG to move
  forward.
• If you draw an imaginary straight line between
  the center of the earth and your own CG, and that
  line falls within the support base of your feet,
  your considered to be balanced and in equilibrium.

15
Stability

• If you move your CG so that the imaginary line
  representing the earth pulling on your CG falls
  outside your feet (support base), you have
  created a lever arm

16
Stability

• If you move your CG so that the imaginary line
  representing the earth pulling on your CG falls
  outside your feet (support base), you have
  created a lever arm
• A lever arm means a torque and a torque means a
  rotation. This is why you fall forwardbecause
  you begin to rotate with the tips of your toes
  acting as the axis of rotation.

17
Centripetal Force

• We discussed the idea of tangential speed and
  what a tangent is.
• Consider a stopwatch being whirled in a circle at
  the end of a rope. Ask yourself What will
  happen of the rope breaks?

18
Centripetal Force

• We discussed the idea of tangential speed and
  what a tangent is.
• Consider a stopwatch being whirled in a circle at
  the end of a rope. Ask yourself What will
  happen of the rope breaks?
• The watch will fly off, not in the same circle,
  but in a straight line that is tangent to the
  circle that it had been prescribing the instant
  before the rope broke.

19
Centripetal Force

• We can then see that the rope provided something
  that brought the watch into a circle. The rope
  forced the watch to move in a circle. This force
  is called centripetal force and is considered a
  center-seeking force. This simply means that
  any force that can be characterized as
  centripetal has a vector pointed toward the axis
  point.