Forces and Motion

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Forces and Motion
5.1 Use measurement time-distance graphs to
represent the motion of an object in terms of its
position, direction or speed.
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Motion

• Motion is a change in position of an object with
  respect to time.
• The following terms are used to describe and
  measure motion.
• Position
• Direction
• Speed

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Position

• Position the location of an object. Change in
  position is measured by distance (length of the
  path) moved from one position (reference point)
  to another.
• What is a reference point?
• Class demonstration One volunteer and the rest
  of the class is split into two groups. This
  activity will illustrate the idea of a reference
  point.

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Reference Point is a place or object used for
comparison to determine if something is in
motion. An object is in motion if it changes
position relative to a reference point.
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Direction

• Direction is the relationship of the position
  of a moving object to another position.

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Speed

• Speed is the rate of change in position or
  rate of motion. How long it takes to move from
  point A to B.
• Speed does not necessarily mean that something
  is moving fast.

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Average Speed

• The average speed of an object tells you the
  (average) time at which it covers a given
  distance.
• Average speed is the result of the total distance
  divided by the total time taken.

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Calculating Average Speed(v d/t)

• v d/t where
• v is the average speed of an object
• d is the distance or length of the path of the
  object
• t is the time taken to cover the path
• Speed is measured using the following types of
  units
• meters per second (m/s)
• kilometers per hour (km/h)
• miles per hour (mph)

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What is the difference between speed and velocity?
Velocity is speed with direction
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Vd/t
td/v
dvt
d
v
t
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TO HELP SOLVE EQUATIONS, HERE IS A STEP BY STEP
GUIDE TO FOLLOW. G U E S S
G find your Givens U what is your Unknown
(trying to find) E what is the Equation you
need? S Substitute your givens S - Solve
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Examples

• Calculate the speed of an object using the
  following information
• t 35 s and d 50m
• Step 1 GUESS
• Givens are t 35 s and d 50 m
• Unknown v
• Equation v d / t
• Substitute v 50 / 35
• Solve v 50 divided by 35

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Examples

• Suppose a cyclist travels 32 kilometers during
  the first two hours of riding, and 13 kilometers
  during the next hour. Calculate the average
  speed
• -total distance 32km 13km
• -total time 2h 1h
• Average speed 45km/3h 15km/h or
• 15 kilometers per hour

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Examples

• Use the speed equation to determine how far an
  object traveled.
• v7m/s
• t3s
• How far did the object travel?
• Rearrange vd/t
• dvt
• d7m/s(3s)
• d21m

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• How long will it take to get to Atlanta, GA for a
  Falcons game from Greenville, SC (145 miles or
  233 km). You know you can travel about 70 mph?
• 2. If a bamboo plant grows 28 centimeters in 11
  days, what was the average speed the plant grew
  per day?
• 3. A soccer player was practicing on the soccer
  field last week. He ran back and forth on the
  field for a total of 750 yards. His average speed
  was 12 yards per second. How long did it take him
  to finish?

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Graphing Speed

• Do you think it is possible to represent speed
  using a graph?
• If so, what type of graph would you use?
• Line graph, bar graph, circle graph????

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• When graphing speed you would use a line graph.
• A line graph shows the relationship between
  distance and time and how it relates to speed.
• The slope of the line gives us information about
  the speed and direction of an object.

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• You graph speed by taking measurements of time
  and distance.
• For instance The following measurements were
  taken on how fast a turtle walks along a path.

Time (h) Distance (m)
0 0
1 5
2 10
3 15
4 15
5 15
6 10
7 5
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B
C
A
At position A, is the object moving away from or
towards the reference point? At position C, is
the object moving away from or towards the
reference point?
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The flatter the slope, the slower the speed.
The steeper the slope, the faster the speed.
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When the slope of the line is horizontal to the
x-axis, the speed is zero (the object is not
moving)
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Examples

• Lets graph the motion of a drag racer.

Time (s) Distance (m)
0 0
5 20
10 40
15 60
20 80
30 100
40 120
Have to allow for a 25 and 35 on your X axis!
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First, we need to label the data x and y.
X axis
Y axis
Time (s) Distance (m)
0 0
5 20
10 40
15 60
20 80
30 100
40 120
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Next, draw and label the graph.
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Now, you need to plot the points.
Time (s) Distance (m)
0 0
5 20
10 40
15 60
20 80
30 100
40 120
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Practice Problem

• Graph the speed of an object as it travels down
  hill.

Time (s) Distance (m)
0 0
1 2
2 5
3 9
4 15
5 20
Time (s) Distance (m)
0 0
1 10
2 8
3 5
4 3
5 1
Graph the speed of an object as it travels up
hill.