Introductory lesson on describing motion for the 9th grader.

1. Describing Motion
Chapter 2: section 1
Tuesday 9/26/13

2. 2 Goals for this lesson
1. Describe motion
2. Perform calculations to determine speed

3. Motion and Position
• A reference point is needed to determine the
position of an object
• Motion occurs when an object changes its
position relative to a reference point
– Ex: How do people in a car know they are moving?
– Ex: Throw a ball, how do you know it moved

4. Distance vs Displacement
• Distance - how far an object has moved
– meter (m)
– Ex: It takes 4 laps around a 400m track to make
approximately a 1 mile race. What is the total
distance in meters?
• Displacement – the distance and direction of
an object relative to the starting point
– Ex: a person walks 20 m North, turns walks
10 m West, and then 20 m South, What is
the displacement?

5. Speed
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•
•
•
•
Speed = s
Distance = d
Time = t
Most common unit = meters per second (m/s)
speed=Total distance traveled ÷ total time
Distance
Speed
Time
• This picture will help with solving
problems mathematically without
knowing Algebra!!

6. Practice problems
1. A passenger elevator travels from the first
floor to the 60th floor, a distance of 210 m, in
35 sec. What is the elevator’s speed?
2. How far does a car travel in 0.75 hours if it is
moving at a constant speed of 88 km/hour?
3. A motorcycle is moving at a constant speed
of 40 km/h. How long does it take to travel
10 km?

7. Homework
Speed worksheet
Tomorrow – Motion detector lab

8. Monday 9/30/13
• Pick up – 9.30 Reinforcement section 1

9. Goals for the lesson
1. Define speed terms
2. Interpret a position time graph
3. Perform calculations to determine velocity

10. Opener for Monday 9/30/13
1. Describe how the skier’s
velocity changes during
the race.
2. Why does the skier’s
velocity increase as he
races downhill?
3. How does being in a tuck
position affect a skier’s
motion?

11. Speed Terms
• Constant speed – if you maintain the same
speed over a time interval
• Changing speed – speed up or slow down over
a time interval
• Average speed - describes the speed of
motion when speed is changing
• Instantaneous speed – the speed at a given
point in time

12. Graphing Motion
• Time is plotted on the x axis
• Distance traveled is plotted on the y axis
• Slope of a distance-time graph = velocity (speed)
– Steeper line = faster
– Horizontal line = not moving, no speed
• Connect the dots with a straight “best fit” line not
a dot-to-dot line
– Easier to extrapolate data in between points

13. Position (m)
Interpreting a graph
• When is the object stopped? How do you know?
• When is it moving the fastest? slowest? Explain

14. Velocity
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•
•
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Velocity symbol = v
Displacement = x
Time = t
Includes the speed of an object but also the
direction of its motion.
• displacement ÷ total time = velocity
Displacement
Velocity Time

15. Homework
• Reinforcement sec 1
• Quiz Wednesday
– speed and velocity calculations
– interpreting graphs
– describing motion