Hopefully the motion lab helped you to solidify your understanding of motion. By moving in a controlled fashion and observing the characteristics of a graph of that motion you can make connections. What happens when you increase your speed? How does a graph of position versus time appear if the velocity is constant?

This week we will continue to work with the quantities that we use to describe motion and again our emphasis will be on the graphical representations of these quantities. This week, however, we will be using a computer simulation. The simulation will accurately describe the motion of a ball on an inclined plane without frictional energy losses. You probably have found that it was difficult to mimic some of the features found on the motion graphs. It is especially hard to move with a constant acceleration. A ball on an inclined plane experience a downward force that guarantees uniform acceleration so long as the incline plane angle is constant and the energy losses due to the frictional forces (e.g. wind resistance) are negligible. The simulation program graphs and track is therefore ideal for studying uniform acceleration.

Some Tips:

On possible area of confusion is the use of the + and - sign. To get the sign correct:

  1. Establish what +x means. You must choose a direction as the positive direction and an origin (x=0 location). Whenever an object is at a location that is on + side of zero it has a positive value. This is usually obvious to the student.
  2. A positive velocity means that the object is moving in the positive x direction. The final x is always more positive that the initial. If you are observing the motion for a brief period it ends up in a more positive location than when it started. Students often get confused on this point so be sure it is clear. The main difficulty arises when dealing with negative values for position. If something starts at location -10 and ends up at location -8 they are moving in a positive direction. Point you arm in the direction of motion. If you are pointing towards + infinity you have a positive velocity.
  3. The most difficult quantity is acceleration. My advice is to imagine a string tied to the moving object. How would you pull on the string to get the observed motion. If you need to pull in the positive direction then the acceleration is positive. If you need to pull in the negative direction you have a negative acceleration. Here are some examples:
Increase speed in the + direction positive pull moving faster in + direction has a positive acceleration
Slow down while going in + dir negative pull moving slower in the + dir is a negative acceleration
Slow down while going in - dir positive pul moving slower in the - direction is positive acceleration
Speed up in the - direction negative pull moving faster in the - direction is negative acceleration
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  • Notice that both getting faster and getting slower can be a sign of positive acceleration.
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    ALSO

    This week we will begin working with spread sheets. Our goal will be to use the equations for uniformly accelerated motion in one direction to generate graphs. We will define cells, use formulas, generate graphs. If you want to get a head start you can begin the spreadsheet work described in the lab manual before coming to lab. If you bring a disk with your work saved then you can copy any work done before lab to the lab computers.

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    This weeks quiz. Read the lab in the manual and be sure you glance at any materials that are available for this week's lab on the web.

    USE BLACKBOARD