Transcript Part III - Otterbein

Pool Billiard can be viewed as elastic
collision in 1D if balls are hit head on.
Professional tables have balls of equal
mass. What happens if the white ball
hits the 8 ball head on (ignore friction)?
• White ball slows down, both balls move after collision
• White ball stops, 8 ball moves with white ball’s velocity
• White bounced back ( neg. velocity), 8 ball moves forward
slowly
• White ball stops, 8 ball moves forward with less than white
ball’s velocity
Pool Billiard can be viewed as elastic
collision in 1D if balls are hit head on.
Bar tables have a heavier white ball.
What happens if the white ball hits the 8
ball head on (ignore friction)?
• White ball slows down, both balls move after collision
• White ball stops, 8 ball moves with white ball’s velocity
• White bounced back ( neg. velocity), 8 ball moves forward
slowly
• White ball stops, 8 ball moves forward with less than white
ball’s velocity
Collision Problem Solving
• Choose your system
• Is momentum conserved, i.e. are only internal forces
acting on the system’s constituents?
• Draw two diagrams: initial and final situation
• Choose a coordinate system, in particular + and –
directions
• Apply monetum conservation equations
• If elastic collision: apply kinetic energy conservation
equation
• Solve for unknowns
• Check results (reasonable?)
Example: Inelastic collision
• Two balls of clay with velocities v1 and v2
collide. After collision they are stuck
together, what is their velocity?
Example: Elastic collision
• A white billiard ball of 100g and v=2m/s
collides head-on with the 8-ball of 90g at
rest.
• What are the velocities of the balls right
after the collision?
Example: Collision in 2D
• Neutron hits Helium target elastically with
v=6.2 10^5 m/s and Helium off at an angle
of 45 degrees.
• What are the velocities (vectors!) of the
protons after the collision?
A ladybug sits at the outer edge of a
merry-go-round, and a gentleman bug
sits halfway between her and the axis of
rotation. The merry-go-round makes a
complete revolution once each second.
The gentleman bug’s angular speed is …
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… half the ladybug’s.
… the same as the ladybug’s.
… twice the ladybug’s.
… impossible to determine.
A ladybug sits at the outer edge of a merry-goround, that is turning and slowing down. The
vector representing her angular velocity is in
the …
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•
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-z direction
+z direction
+y direction
zero
z
y
x
A ladybug sits at the outer edge of a merrygo-round, that is turning and slowing down.
At the instant shown, the radial component of
the bug’s (Cartesian) acceleration is in the …
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•
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-x direction
+y direction
+z direction
Zero
z
y
x
A ladybug sits at the outer edge of a merry-goround, that is turning and slowing down. At
the instant shown, the bug’s angular
acceleration is in the …
•
•
•
•
-z direction
-y direction
+y direction
+z direction
z
y
x
A ladybug sits at the outer edge of a merry-goround, that is turning and slowing down due to
a force exerted on its edge. At the instant
shown, the torque on the disc is pointing in …
•
•
•
•
-z direction
-y direction
+y direction
+z direction
z
y
F
x
A ladybug sits at the outer edge of a merry-goround, that is turning and slowing down due to
a force exerted on its edge. The angular
momentum of the bug is pointing in …
•
•
•
•
-z direction
-y direction
+y direction
+z direction
z
y
F
x
What is A x A ?
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Zero
A
-A
A2