Chris Maloney

 

Chapter 1 Answers

Review Questions:

1.    A.  According to Aristotle,  Natural motion is what an object does because of its nature.  For instance, the nature of earth is to be at  rest at the center of the earth. Thus 'earthier' things fall the fastest (according to Aristotle/remember that without air resistance, all objects fall with the same acceleration towardthe center of  the earth as Galileo found).  It  was 'natural' for heavenly bodies to move in circular paths.  Forced or violent motion is caused by a push or a pull for Aristotle. 

2.    Since the natural state of earthly objects is rest in their proper 'home'; Aristotle taught that rest is  the rule and motion (any  kind) is  the exception to the rule.  Therefore any kind of motion required a cause or explanation.

4.    The authors probably  wanted you to say 'experiment' judging from what they say on  pages 15 and 16.  While largely true, this isn't the whole picture.  Galileo made use of  mathematics (geometry), experimentation, and philosophical dialogue in order to extend knowledge.  Some of his most important scientific conclusions are found in  two long philosophical dialogues called 'The Two New Sciences' and 'Dialogue concerning the two chief world systems:  Copernican and Ptolemaic'.  Galileo was deliberately fitting in with the western philosophical tradition by writing up his results this way.   Modern scientific papers are no longer written in this style.  The way that scientific results are communicated is at least as important as how the scientist arrives at them.   Galileo wasn't the first to use experiment to determine scientific  truth.  However, his careful work and his emphasis on the importance of experimentation set a new standard for the role  of experiments in science.  For this and other reasons, he is given credit  as one of the founders of modern science.

5.    Inertia

7.    My weight (and yours) would be greater on  the moon, all other things being equal.  Our masses, however, would remain the same.

9.    Less (about one sixth as much or about 1.7 m/s2)

11.   Magnitude and direction

13.   20 N

16.   They are equal but opposite in direction.  Note:  this is not due to Newton's 3rd law but is because your body is in static equilibrium!

19.  Frictional force increases with the velocity  of the object.

*  For exercises 22-30 I chose to select only three to answer here:

22.  Velocity means speed in a given direction.   For example, 50 miles per hour to the east is a velocity while 50 mils per hour is  only a speed.

29.  It might help to think of the units of acceleration as being in meters per second each second instead of m/s2 though both ways of expressing it are correct.  For example, the acceleration due to gravity is 10 meters  per  second each second since a free-falling object speeds  up by 10 m/s each second that elapses.

30.  By 10 m/s!  See #29!

 

 

Exercises  

12.   150 N

23.   Wrong:  the dragster cannot be moving at a constant velocity if it is changing direction.  It can, however, be moving at a constant speed

24.  2 km/h

25.   Not at all:  his speed relative to the bank in this case will  be zero!

32.  zero!  Read the question again ;-)

Problems

1.    a)  50 N   b) 10 N or -10N depending on which force is thought to act in the + direction.

2.    a) zero    b)  100 N

3.   1000 N up the pole

4.   2000 years

5.  -10 km/h/sec  or -2.8 m/s2