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MASTERING PHYSICS CHAPTER 8 CONCEPTS

# MASTERING PHYSICS CHAPTER 8 CONCEPTS - 8.1 Visualize Solve...

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8.1. Visualize: Solve: Figure (i) shows a weightlifter (WL) holding a heavy barbell (BB) across his shoulders. He is standing on a rough surface (S) that is a part of the earth (E). We distinguish between the surface (S), which exerts a contact force, and the earth, which exerts the long range force of gravity. Figure (ii) shows the barbell, the weightlifter, and the earth separated from one another. This separation helps to indicate the forces acting on each object. Figures (iii) and (iv) are free body diagrams for the barbell and the weightlifter, respectively. Altogether there are four interactions. There is the interaction between the barbell and the weightlifter, the weightlifter and the surface of the earth (contact force), the barbell and the earth, and the weightlifter and the earth. The interaction between the barbell and the weightlifter leads to two forces: r F WL on BB and r F BB on WL . These are an action/reaction pair. The interaction between the weightlifter and the surface of the earth is a contact interaction leading to r n S on WL and r n WL on S . These two forces also constitute an action/reaction pair. The weight force r w E on BB has its action/reaction force r w BB on E , and the weight force r w E on WL has its action/reaction force r w WL on E .

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8.2. Visualize: Solve: Figure (i) shows a softball player (P) with a ball (B) in her hand that has come forward beside her head and is just about ready to release the ball. We have represented the earth (E) and its rough surface (S). Contact forces exist between the surface and the softball player. Figure (ii) shows the ball, the player, and the earth separated. This separation helps to indicate the various forces on each object. We have altogether 6 interactions. The action/reaction pairs of all the forces have been indicated by dotted lines. Figure (iii) shows the free-body diagrams for the ball and the softball player.
8.3. Visualize: Solve: Figure (i) shows the head-on collision of a bowling ball (BB) and a soccer ball (SB) on a hard surface (S) of the earth (E). There are 3 types of interactions in the present case: between the bowling ball and the soccer ball, between the earth and the balls (long-range force of gravity), and between the balls and the surface (contact force). Figure (ii) shows the bowling ball, the soccer ball, and the surface separated from one another. The force on the bowling ball due to the soccer ball r F SB on BB and the force on the soccer ball due to the bowling ball r F BB on SB make an action/reaction pair. The weights r w E on SB and r w SB on E are an action/reaction pair, and so are the weights r w E on BB and r w BB on E . The contact forces r n S on BB and r n S on SB have action/reaction forces in r n BB on S and r n SB on S , respectively. All the action/reaction pairs are indicated by dotted lines. Figure (iii) shows the free-body diagrams for the bowling ball and the soccer ball.

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8.4. Visualize: Solve: Figure (i) shows the mountain climber (C), the rope (R), the bag of supplies (B), the surface of the mountain (S), and the earth (E). To indicate the forces on each of the various objects, we have separated C, R, B, S,
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MASTERING PHYSICS CHAPTER 8 CONCEPTS - 8.1 Visualize Solve...

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