Representing Motion Linear motion: motion in a single dimension (in a line). A rate tells how quickly something happens. Rate: A quantity divided by time

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Representing MotionLinear motion motion in
a single dimension (in a line).A rate tells how
quickly something happens. Rate A quantity
divided by time
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Motion is Relative

• Frame of Reference point of view of the
  observer
• If something is relative, it depends on the frame
  of reference.
• When we discuss the motion of something, we
  describe its motion relative to something else.
• Usually, when we discuss the speeds of things on
  Earth, we mean the speed with respect to the
  Earths surface.

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Speed

• Speed is a measure of how fast something is
  moving.
• the rate at which distance is covered.
• Speed the distance covered per unit of time.
• SI unit m/s
• Ex 100 km/hr, 55 mph, 30 m/s
• Equation v d / t
• v speed (m/s)
• d distance (m)
• t time (s)

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• Instantaneous speed
• the speed at any given instant
• Ex speedometer
• Average speed
• the total distance covered divided by the time
  interval
• Average speed does not indicate changes in the
  speed that may take place during a trip.
• BOTH instantaneous and average speeds indicate
  the rate at which distance is covered.

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Physics Problem Solving Strategy

1. List your variables
2. Givens
3. Unknown variable
4. If need be, convert variables to SI units
5. Choose the equation that matches your variables
6. Substitute variables in to the equation
7. Solve

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Check Your Understanding

• If a cheetah can maintain a constant speed of 25
  m/s, it covers 25 meters every second. At this
  rate, how far will it travel in 10 seconds?
• d ?
• v 25 m/s
• t 10 s
• v d /t
• 25 m/s (d) / (10s)
• d (25 m/s)(10s)
• d 250m

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Check Your Understanding

• In one minute?
• d ?
• v 25 m/s
• t 60s
• Convert minutes ? seconds
• v d / t
• 25 m/s (d) / (60s)
• d (25 m/s)(60s)
• d 1500m

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Velocity

• When we say that a car travels 60km/hr, we are
  indicating its speed. When we say that a car is
  traveling 60km/hr to the north, we are indicating
  its velocity.
• Velocity the speed in a given direction
• SI unit m/s
• Ex 100 km/hr East, 55 mph North, 30 m/s
  Southwest
• Equation v d / t
• Speed is a description of how fast an object
  moves velocity is how fast it moves AND in what
  direction .

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Check Your Understanding

• The speedometer of a car moving northward reads
  100 km/h. It passes another car that travels
  southward at 100 km/h. Do both have the same
  speed? Do they have the same velocity?
• Both cars have the same speed, but they have
  opposite velocities because they are moving in
  opposite directions.

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• Constant Velocity
• Constant velocity requires both constant speed
  and constant direction.
• Motion at constant velocity is in a straight line
  at constant speed.
• Changing Velocity
• Constant speed and constant velocity are not the
  same thing.
• A body may move with constant speed around a
  curved path, but it does not move with constant
  velocity because the direction changes at every
  instant.