Motion

1
Motion

• To describe motion accurately and completely, a
  frame of reference is necessary.
• A frame of reference is a system of objects that
  are not moving with respect to one another.
• Relative motion is the motion in relation to the
  frame of reference.
• Bus and bus stop.

2
Is Seeing Believing?

• Reference point is the point from which movement
  is determined.
• To measure movement, some point must be
  considered as nonmoving.
• Earth is the most common frame of reference
• However
• Earth rotates on its axis at almost 1100
  miles/hour.
• Earth moves around the sun at over 68,000
  miles/hour.
• The whole galaxy is rotating at about 490,000
  miles/hour

3
Measuring Distance

• Distance is the length between two points.
• The SI unit for distance is a meter.
• Longer distances kilometer (km)
• Shorter distance centimeter (cm)
• Displacement is the direction from the starting
  point and the length of a straight line from the
  starting point to the ending point.
• Vector

4
Combining Displacements

• When you have two displacements in the same
  direction you add them together.
• When you have two displacements in opposite
  directions you subtract them.
• If you have a displacement in two directions, it
  is the distance and direction from the starting
  point to the ending point. This is the resultant
  vector.

5
Speed

• Speed is the ratio of the distance an object
  moves to the amount of time the object moves.
• Speed (m/s) distance (m) v d
• time (s) t
• Average speed is computed for the entire
  duration, and instantaneous speed is measured at
  a particular instant.
• Average speed total distance (m) v d
• total time (s) t
• - Instantaneous speed is the speed at a given
  moment. Example cars speedometer

6
v d/t

• Example below
• Total distance is 5 miles
• Total time is 0.2 hrs
• Average speed 25 mph (miles per hour)
• http//www.glenbrook.k12.il.us/g
  bssci/phys/Class/1DKin/U1L1d.html

7
Graphing Speed

• The slope of a distance-time graph is the speed
  of an object.
• m y2 y1 v d2 d1
• x2 x1 t2 t1
• Green Constant
• Blue Acceleration
• Red Changing speed

8
Velocity

• Velocity is a description of both speed and
  direction of motion.
• Velocity is a vector.
• A vector is a quantity that has direction. It is
  represented by an arrow. (?) Longer an arrow the
  greater the vector.
• A change in speed or direction is a change in
  velocity.
• You can have a constant speed but a different
  velocity.

9
Acceleration

• Acceleration can be described as a change in
  speed, changes in direction or both.
• A change in velocity
• Acceleration is a vector.
• Acceleration velocity final velocity original
• Time
• a vf vi
• time
• Unit m/s2

10
Types of Acceleration

• Positive acceleration speeding up
• Free fall is a positive acceleration towards the
  earth due to gravity. (9.8 m/s2)
• Negative acceleration slowing down
• Deceleration
• Centripetal acceleration is towards the center of
  the circle.
• Constant acceleration is a steady change
  in velocity.
• Instantaneous acceleration is how fast
  the velocity is changing at a given
  moment

11
Graphing Acceleration

• In a distance-time graph the acceleration of an
  object is represented by a curved line.
• In a velocity-time graph the acceleration of the
  object is the slope of the line. It is
  represented by a straight line.