Ch. 2 Linear Motion

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2
Relative motion

• All objects in the universe move with respect to
  something.
• We say that motion is relative because there is
  no point in the universe that is standing still.

3
What is speed?

• A quantity divided by time is called a rate. Ex.
  speed, acceleration, velocity
• Speed is any distance divided by time. There are
  many ways to express speed miles/hr, meters/sec,
  etc.

4
Average and instantaneous speed

• Speed can be either instantaneous or average.
• Instantaneous speed is the speed of an object at
  a particular instant.
• Average speed is the total distance divided by
  the total time.

5
What is velocity?

• Velocity is an objects speed in a given
  direction.
• A car rounding a curve with the speed control on
  has a constant speed but changing velocity.

6
What is acceleration?

• Acceleration is the rate at which speed is
  changing or velocity divided by time, av/t.
• Acceleration can be positive, speeding up or
  negative, slowing down (decelerating).

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Acceleration due to gravity

• Gravity causes all objects to accelerate towards
  the earth. The longer they fall, the more speed
  they acquire.
• A brick that breaks loose from the top of a
  building falls farther the last second than the
  first.

8
Atmospheric friction

• We live on a planet with a thick atmosphere. This
  causes objects falling through it to slow down.
• Without air objects will experience constant
  acceleration. (Ex. On the moon)

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What is g ?

• Objects falling near the Earth experience an
  acceleration of 9.8 m/s2 (32 ft/s2)
• This is called g and is often rounded to 10 m/s2

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Useful Formulas

• Vd / t
• d v x t
• t d / v
• v a x t
• d ½ at2
• V avg v f v0 / 2
• Vvelocity, aacceleration, ttime, ddistance