1. N3 – Forces from Motion
Get a spring
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2. The Kinematic Chain
A particle moves along the x axis according to the equation x = t t2 where x is in meters and t is in seconds. At t=3.00 s, find (a) the position of a particle, (b) its velocity, (c) its acceleration.
The object that is sliding only, will be moving with a faster velocity at the bottom. The ball is rolling and thus, some energy from the gravitational potential energy changes the translational kinetic energy and the rotational energy.
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3. Graphical Analysis of Motion
v(t) is slope of r(t) graph
a(t) is slope of v(t) graph
Derivative is slope, so we can link r, v and a graphically as well as mathematically
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4. Net Force Diagrams Construct a free-body diagram.
Copy the force arrows from the diagram in sequence (tip-to-tail).
Draw a double-line arrow to show the vector sum.
b) Superimpose circle centered on P; divide circumference of circle into an equal number of spaced units; how many units does the angle span
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5. Qualitative Example Skier going down slope (Fig N3.1) FKF FD FN Fg
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6. Practice Problem
N3B.1 Draw a free-body diagram and a net-force diagram for a moving motorboat whose motor has just run out of gas. D
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7. Third-Law Pairs
When objects A and B interact, the force the interaction exerts on A is equal in magnitude and opposite in direction to the force it exerts of B.
Force pairs connected by Newton’s 3rd Law:
Each force in the pair must act on a different object.
Each must reflect the same interaction.
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8. Second-Law Pairs Ex: Normal force and weight, when object is at rest.
Force pairs connected by Newton’s 2nd Law:
Act on the same object
Arise from different interactions
Act along same axis
Are = b/c a=0 along that axis
Ex: Normal force and weight, when object is at rest.
What if object is accelerating, like box in an elevator??
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9. Coupling Forces
Compare the forces exerted by the blocks on each other as they move on a table with some friction. Draw free-body diagram for each block. Determine if A block A exerts a greater force B block B exerts a greater force C the forces are equal
Solve together with class. Compare to FBD of mtot=mA + mB.
Should get C
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10. Coupling Forces
Compare the forces exerted by the blocks on each other as they move on a table with some friction. Draw free-body diagram for each block. Determine if A block A exerts a greater force B block B exerts a greater force C the forces are equal
Ditto
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11. Third Law Pair Activity
Equipment
Wired force probe
Wireless force probe
Open Logger Pro
Select Connect Interface, Wireless, and select the name of your wireless probe
In the top right corner you will see two tabs, one for each probe. Click on each tab and select zero sensor from the calibrate menu. On one of the sensors, select change direction.
Connect the hooks on the force probes together and pull and push until the values are different. Record your results.
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12. Group Problems N3B.4 N3B.6 N3B.9 N3S.2 N3S.5 Unit IV, Worksheet 4
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