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PHY 121 Ch 4 Lecture

# PHY 121 Ch 4 Lecture - Lecture 5 Tuesday January 24 1 A...

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1 Lecture 5 Tuesday, January 24

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2 A force of 10 +6 N is close to A. The sun’s gravitational force on the Earth. B. The weight of a blue whale. C. The weight of a medium apple. D. The electric attraction between the proton and the electron in the hydrogen atom.
3 While an object is in motion, the net force acting on it disappears A. The object immediately stops. B. The object continues moving at a slower speed for a while, and eventually stops. C. The object may slow down or speed up, depending on the direction of the net force. D. The force continues moving at constant velocity. The final constant velocity is the velocity it had at the time the net force vanished.

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4 The net force acting on an object and the object’s acceleration: A. have the same direction. B. have the same direction only if the object starts from rest. C. have the same units. D. none of the above.
5 In an action-reaction force pair the action component A. is the force exerted by the largest mass. B. is the force exerted by the smallest mass. C. is the strongest of the two forces. D. cannot be identified.

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6 Forces The reason why the world is interesting is that objects interact . In physics, the interaction is characterized by forces . • A force is a push or a pull that acts on an object. This force is always caused by some other object. • Mathematically,a force is a vector with magnitude and direction.
7 Force diagrams Represent the object as a particle.

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8 Force diagrams II Draw the force vector as an arrow pointing in the proper direction and with a length proportional to the size of the force.
9 Force diagrams III Place the tail of the force vector on the particle.

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10 Force diagrams IV Place the tail of the force vector on the particle.
11 The net force ! F 1 F 2 ! F ! ! F ! = ! F 1 + ! F 2 + ! F 3 + ...

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12 Mass Every object has a property called mass.
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