Motion

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Motion

• Chapter 2
• Part 1

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What kind of motion will this car undergo?
3
Motion is Relative

• Even things that appear to be at rest move. They
  move with respect to, or relative to, the sun and
  stars.

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Speed

• Speed (v ) The measure of how fast something is
  moving.
• Distance / Time
• For example 25 km/h
• or 25 kilometers / per one hour
• Units for speed are (m/s) and (km/h)

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Differences in words

• Displacement how far you got from your starting
  point as measured in a straight line.
• Distance how far you actually travelled.

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Instantaneous Speed

• Instantaneous Speed The speed at any instance.

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Average Speed

• Average speed
• If we travel 240 kilometers in 4 hours, what is
  our average speed?
• 60 km/h

Total distance covered
v

Time interval
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Velocity

• Speed and Velocity are not interchangeable terms.
  
• Velocity is speed in a given direction.
• A car traveling 60 km/h only expresses speed, but
  a car traveling 60 km/h going north expresses
  velocity.

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Constant Velocity

• Constant Velocity requires both constant speed
  and constant direction.
• In order to have constant direction, the object
  must be moving in a straight line!

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Changing Velocity

• Changing Velocity If either speed or the
  direction (or both) is changing, then the
  velocity is changing.
• You can drive in a circle at constant speed, but
  your direction is continuously changing.

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Acceleration

• Acceleration The rate _at_ which velocity is
  changing.
• acceleration

? v
a

? t
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Acceleration

• In physics, the term acceleration applies to
  decreases as well as increases in speed.
• Typically in a college physics class you would
  use the term negative acceleration instead of the
  common term deceleration.
• a refers to a ? in direction as well as a ? in
  v.

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Acceleration
Equation is

• acceleration

? v
time interval
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Acceleration

• Suppose a car moving in a straight line steadily
  increases its speed each second, first from 35 to
  40 km/h, then from 40 to 45 km/h, then from 45 to
  50 km/h.
• What is its acceleration?

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Acceleration

• Answer We see that the speed increases by 5 km/h
  during each 1-s interval.
• The acceleration is therefore 5 km/hs during
  each interval.

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