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.

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Vector and Scalar Quantities

• Scalar a quantity that requires magnitude only
• Number and units ONLY
• Ex Speed, mass, time
• Vector a quantity that requires both magnitude
  AND direction
• Number, units, AND direction
• Ex Velocity, acceleration, force

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Check Your Understanding

• Is height a scalar or vector quantity?
• Scalar. Height only includes magnitude (how big
  the number is) only and NOT direction. You are
  58 tall, not 58 to the east.

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Adding Vectors

• An arrow is used to represent the magnitude
  direction of a vector quantity.
• The length of the arrow indicates the magnitude
  of the vector quantity.
• The direction of the arrow represents the
  direction of the vector quantity.
• When more than one vector combines together, both
  the magnitude AND the direction matter.
• The sum of 2 or more vectors is called the
  resultant.

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• Arrows that point in the same direction are added
  together to find the resultant.
• 4 m/s N 3 m/s N 7 m/s
• Arrows that point in opposite directions are
  subtracted to find the resultant.
• 4 m/s N 3 m/s S 1 m/s
• When arrows are at right angles to each other,
  the diagonal of a rectangle will determine the
  resultant.
• Use the Pythagorean theorem a2 b2 c2
• (4m/s N)2 (3 m/s E)2 16 9 25 (5 m/s NE)2

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Check Your Understanding

• A boy is riding his bike down the street at a
  speed of 10 m/s. A gust of wind came out of
  nowhere headed towards the boy. If the wind is
  traveling 3 m/s, what will the boys new speed
  be?
• Since the boy and the wind are moving in opposite
  directions, we need to subtract their speeds to
  find the resultant.
• 10 m/s 3 m/s 7 m/s

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Position - Time graphs

• Position-Time graphs show the distance covered
  over an elapsed time
• Aka Distance-Time graphs and Displacement-Time
  graphs
• Time is always the independent variable

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• Position (distance) is always the dependent
  variable
• The slope of a Position-Time graph is equal to
  velocity
• Slope rise/run
• Slope position / time
• Velocity position / time
• The steeper the slope, the faster the velocity
• A positive slope is forward motion
• A negative slope is moving backwards
• A zero slope is NOT moving at all

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Check Your Understanding

• Which person is moving faster, the red or blue
  jogger?
• The red jogger. The red joggers line has a
  steeper slope and therefore a faster speed.

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Check Your Understanding

• Are both joggers moving forwards or backwards?
• Forwards. The slope is positive, meaning that
  the distance increases over time.

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Check Your Understanding

• At what time does Person B pass Person A?
• At 45 seconds. The lines intersect at this time
  and both runners are at the same position at the
  same time.