Velocity

1
Velocity
2
Describing Motion

• Describing an objects motion with only its
  starting and stopping point (displacement),
  doesnt describe the motion very well.
• Knowing the speed of the object is also important

3
Average Velocity

• The average velocity of an object is defined as
  the displacement divided by the time interval.
• This value is normally expressed in meters/second
• This formula is extremely important in our study
  of motion.

4
Average Velocity

• The average velocity of an object can be positive
  or negative depending on the sign of the
  displacement.
• In this case if you take a trip to a friends
  house 370km to the west (negative direction)
  along a straight highway and the trip took 5
  hours, your average velocity would be 74km/hr.

5
Average Velocity

• This value is an average.
• You probably didnt travel 74 km/hr for every
  second.
• At times you might have stopped or slowed down.
• That means at other times you were traveling
  faster to make up for these delays.

6
Speed and Velocity

• In every day language, speed and velocity are
  used interchangeably.
• In physics, however, there are some distinctions
  between the two
• Speed is a scalar measurement because it only has
  a magnitude.
• Velocity is a vector measurement because it has
  both a magnitude and a direction (positive or
  negative)

7
Problem

• During a race on level ground, Andra runs with an
  average velocity of 6.02 m/s to the east. What
  distance does Andra cover in 137 s?

8
Solution

• If we rearrange the formula for average velocity,
  we can find the distance (displacement) that
  Andra runs.
• Solving we get
• ?d 6.02m/s x 137s
• ?d 824.74m East

9
Significant Digits

• Lets look at the problem we just finished.
• We see that our v is 6.02 m/s(3 digits)
• And our time is 137 s(3 digits)
• There is only one rule of significant digits that
  I would like you to use.
• Your answer needs to have the same number of
  significant digits as your givens (if possible)
• Therefore, we would give 825 m East as an answer

10
Significant Digits

• Sometimes it is not convenient to use this rule
• For example, if our time would have been 99
  seconds (2 sig.figs.), the calculator would give
  a value of 595.98.
• Using two significant digits would be difficult
  so three would work 596 m East