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If we want to calculate the average velocity of an object, we must know two things. First, we must know its displacement: the distance it has covered. Second, we must know the time it took to cover this distance. Once we are in possession of this information, the formula for average velocity is quite simple: average velocity = Δ position / Δ time. In other words, the average velocity is equal to the change in position (final position - original position) divided by the change in time (final time - original time). This calculation will indicate the amount of distance that was covered in each unit of time. Average velocity is a vector, though it will always have the same sign as the displacement (since time is always positive).
1. Which two pieces of information are required to calculate average velocity?
2. What does the symbol Δ mean?
3. What is the relation between the vector arrow in velocity and the direction of displacement?
4. If an object has traveled 6 miles in 30 seconds(not minutes), what is its average velocity?
5. If an object has an average velocity of 25 meters per second, and has been traveling for 12 seconds, how far has it gone?
Before Newton formulated his laws of mechanics, it was generally thought that some force had to act on an object continuously in order for it to move at a constant velocity. This seems to make sense: when an object is briefly pushed, it will eventually come to a rest. Newton, however, determined that unless some other force acted on the object (most notably friction or air resistance), it would continue in the direction it was pushed at the same velocity forever. In this light, a body at rest and a body in motion are not all that different, and, indeed, Newton's first law makes little distinction. It states that a body at rest will tend to remain at rest, while a body in motion will tend to remain in motion. One fact that emerges from this law is that if the net force on an object is zero, it will be possible to find reference frames in which the body has no acceleration.
6. Before Newton, what did physicists believe was necessary to maintain constant velocity?
7. Which of the following forces does NOT prevent an object in motion from remaining in motion?
8. In a total vacuum, what would you expect to happen if an object was given a slight push?
9. According to Newton's first law, there is little difference between the behavior of a body at rest and:
10. Given the context of the passage, what is a likely definition for 'reference frame'?
1. C. In order to determine average velocity, one must know both change in displacement and change in time.
2. B. In physics, the Δ (delta) symbol indicates 'change in.'
3. A. The direction of the vector and the direction of displacement are the same.
4. A. Divide the change in displacement by the change in time to determine average velocity.
5. A. Rearrange the equation for average velocity, so that by multiplying change in time by average velocity you find displacement.
6. A. Physicists did not realize that friction and air resistance were impeding the natural motion of the object.
7. B. Centripetal force would not prevent an object from moving.
8. C. With no resistance, an object set in motion would be expected to remain in motion forever.
9. D. For Newton, the difference between the two bodies is largely a matter of perspective.
10. A. The reference frame of an object is the set of objects to which it is viewed in relation.
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