1. C3 – Interactions transfer momentum
Finish C3 slides
Finish C2 and C3 Lecture Worksheet
C4 - Particles and Systems
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2. Solutions to HW Download ProbViewer 1.4 Password for daily HW problems
Password for daily HW problems
phys130cn
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3. Quiz Problem 1 – C4X.1
Consider a system consisting of two billiard balls on a pool table. If the balls collide, is the interaction between the ball an internal or external interaction?
A. Internal
B. External
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4. Two Minute Problem – C4T.1 mod
Which of the following things does NOT qualify as being an “extended object”?
A. An electron
B. An atom
C. A rock
D. A human being
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5. Force Rate at which momentum flows General Physics Stopped here
Did the C2-C3 lecture worksheet. Most students completed 2 or 3 of the problems. Needed help with first one.
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6. Impulse Questions
In terms of impulse and momentum, why do airbags in cars reduce the chances of injury in accidents?
When jumping from a significant height, why is it advantageous to land with you knees bent?
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7. Mass and Weight
In physics, mass and weight are completely distinct concepts
Where
m = mass (does not = weight), a scalar
= is the gravitational field vector
= weight, a force and vector
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8. Momentum flow and motion - 1
Multitap
The initial arrow show the ball’s initial momentum.
The taps represent the impulse being delivered to the ball due to the gravitational interaction.
You add the tap impulse to the initial impulse to get the momentum after the tap.
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9. Momentum flow and motion - 2
Reservoir
Momentum is only changing in the z direction because there is only a gravitational interaction acting on the ball. The x reservoir and y reservoir don’t change. The x has a positive value for momentum because the ball has a horizontal initial velocity. No interactions act in the x-direction.
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10. Conservation of Momentum
A system’s total momentum is the vector sum of the momenta of its constituent particles
The total momentum of an isolated system is conserved; that is, it does not change with time
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11. Center of Mass is the system’s center of mass
are the positions of the system’s N particles
are the masses
is the system’s mass
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12. Center of Mass, Example Both masses are on the x-axis
The center of mass is on the x-axis
The center of mass is closer to the particle with the larger mass
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13. Center of mass - column vector notation
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14. Think-Pair-Share – C4B.2
Consider a system consisting of two point particles A and B. The particles are 25 cm apart, and the distance between particle A and the system’s center of mass is 5 cm. What is the mass of particle B compared to the mass of A?
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15. Think-Pair-Share – C4B.3
In a certain reference frame, a 0.20-kg point particle lies 22 cm due north of the origin, another 0.15-kg particle lies 38 cm due west of the origin, while a 0.40-kg particle lies at the origin. Locate the center of mass of this system in this reference frame.
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16. Center of mass activity - 1
You will need
Meter stick
Fulcrum
Mass hangers
masses
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17. Center of mass activity - 2
Use column vector notation for two examples
Same mass
Different masses
Find location of and compare to experimental result
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18. System’s Momentum
A system’s center of mass responds to its external interactions exactly as a point particle would respond to those interactions
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19. Think-Pair-Share
A uniform piece of sheet steel is shaped as shown. Compute the x and y coordinates of the center of mass of the piece.
Use column vectors – good Matlab problem
Rcm = (1/M)*((3M/6)[15 5] + (M/6)[5 15] + (2M/6)[10 25])
Rcm = [ ]
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20. Motion of the Center of Mass
A projectile is fired into the air and suddenly explodes
With no explosion, the projectile would follow the dotted line
After the explosion, the center of mass of the fragments still follows the dotted line, the same parabolic path the projectile would have followed with no explosion
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21. Center of Mass
Dick Fosbury introduced a new high jump technique - the Fosbury Flop - at the 1968 Olympics. Raised world record 30 cm!
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22. Inertial Reference Frames
How do we distinguish between an inertial and noninertial reference frame?
Test Newton’s first law
An object in motion stays in motion and an object at rest stays at rest
A reference frame attached to a truck that starts and stops is not an inertial reference frame
Earth and space station okay if we ignore gravitational interaction
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23. Interacting with the earth
Consider the interaction of you and the earth.
If you jump up, you receive an upward impulse from the earth and the earth receives a downward impulse from you.
Using a reference frame attached to the center of mass of the system of the earth and you, the earth does move, but the distance is too small to detect.
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