CH. 2 Notes

1
CH. 2 Notes

• Abbreviated

2
Distance vs. Displacement

• Distance how far an object travels (meters)
• Displacement straight line path between two
  points.

3
Speed

• Speed is the distance an object travels per unit
  time.
• 55 mph or 10 m/s
• Metric (SI) unit is meters/second
• Calculating speed

4
Distance-Time graphs

• Distance Always y-axis
• Time Always x-axis
• Slope of the line speed
• ?y / ?x slope
• Horizontal line no motion
• Steep line greater speed

5
Velocity

• Velocity is speed with a direction
• Ex. 55 mph North
• Because velocity depends on direction as well as
  speed, the velocity of an object can change even
  if the speed of the object remains constant.
• The speed of this car might be constant, but its
  velocity is not constant because the direction of
  motion is always changing.

6
Acceleration

• Acceleration is the rate of change of velocity.
  When the velocity of an object changes, the
  object is accelerating.
• A change in velocity can be either a change in
  how fast something is moving, or a change in the
  direction it is moving.
• Acceleration occurs when an object changes its
  speed, its direction, or both.

7
Speeding Up and Slowing Down
If the acceleration is in the same direction as
the velocity, the speed increases. Acceleration
is positive.
If the speed decreases, the acceleration is in
the opposite direction from the velocity, and the
acceleration is negative.
8
Changing Direction
Any time a moving object changes direction, its
velocity changes and it is accelerating.
9
Calculating acceleration
10
Practice

• A runner covers the last straight stretch of a
  race in 4 s. During that time, he speeds up from
  5 m/s to 9 m/s. What is the runners acceleration
  in this part of the race?
• a 9m/s 5 m/s
• 4s
• a 1m/s/s or 1 m/s2

11
speed-time graphs

• graph shows acceleration
• positive slope (going up) increasing
  acceleration
• negative slope (going down) decreasing
  acceleration
• speed _at_ 0 no motion
• horizontal line constant speed (velocity)