Describing Motion

1
Describing Motion

• Section 2.1

2
SC Standards Covered

• PS-5.1 Explain the relationship among distance,
  time, direction, and the velocity of an object
• PS 5.2 Use the formula vd/t to solve problems
  related to average speed or velocity
• PS 5.6 Represent linear motion of objects on
  distance time graphs

3
Motion

• Motion when an object changes its position
• Reference point- an indicator that orients
  you---the place from which you measure, record,
  or witness an event
• Distance how far an object has moved
• -measured in meters (m)
• Displacement distance and direction of an
  objects change of position from a starting point
  (see pg. 38-39 in text)

4
Displacement
5
Pythagorean Theorem

• Displacement
• a2 b2 c2
• Example Joe walks 4m North turns and walks 3m
  west. What is Joes distance and displacement?

6
Speed

• Speed the distance an object travels per unit
  time
• Speed distance d
• time t
• Units will always be some distance measurement
  divided by some time measurement

7
Types of Speeds

• Average speed total distance traveled divided
  by total time traveled

• Instantaneous speed speed at a given point in
  time.
• This is what is shown on a speedometer

8
Calculating Speed

• Example 1
• Suppose you ran 2 km in 10 min. What is your
  speed?
• s d
• t
• 2 km
• 10 min.
• 0.2km/min.

9

• Example 2
• Sound travels at 330 m/s. If a lightning bolt
  strikes the ground 2 km away from you, how long
  will it take for the sound to reach you?
• 2km 2000 m
• s d
• t
• 330 m/s 2000m
• t
• (330)(t) 2000
• (330)(t) 2000
• 330 330
• t 6.06 s

10
You Try ?

• A passenger elevator travels from the first floor
  to the 60th floor, a distance of 210 m, in 35 s.
  What is the elevators speed?
• A motorcycle is moving at a constant speed of 40
  km/hr. How long does it take the motorcycle to
  travel a distance of 10 km?
• How far does a car travel in 0.75 hr if it is
  moving at a constant speed of 88 km/hr?

11
Velocity

• Velocity speed of an object and the direction
  of its motion
• Speed can remain constant but if the direction of
  the object changes its velocity is changing
• Calculated the same as speed

12
Vector vs. Scalar

• Scalar- magnitude only
• Example distance or speed
• Vector- magnitude and direction
• Example displacement or velocity

13
Graphing Motion

• Graph distance on the y-axis and time on the
  x-axis

• Slope rise distance speed
• run time

14
Your turn!

• Suppose a bus is traveling along a highway. It
  travels 100 km in the first 2 hrs and 120 km in
  the second 2 hrs. It stops for one hour, then it
  finishes the trip by going 100 km in two hours.
  Draw a distance verses time graph of the buss
  motion.