Physical Science Ch 11

1
Physical Science Ch 11

• Motion

2

• To describe motion, you must state the direction
  the object is moving as well as how fast the
  object is moving.

3

• Motion - a change in position
• How do you know something has moved?
• You also need a frame of reference.
• A frame of reference is a system of objects that
  are not moving with respect to one another.
• People on a train platform see a train moving
  rapidly past them
• The people on the train look at one another and
  they dont seem to be moving at all.

4

• Distance - the length of a path between two
  points.
• SI Unit is meter (m)

5

• Displacement - the length from the starting point
  to the ending point
• Vector - a quantity that has magnitude and
  direction. Displacement is an example.

This is a vector. It shows displacement from A
to B. Its magnitude can be size, length or
amount. We use arrows to represent vectors. The
length of the arrow shows the magnitude
6

• When two vectors have the same direction, you can
  add their magnitudes.
• When displacement vectors are in opposite
  directions, the magnitudes subtract from each
  other.

These vectors are in different directions. The
resultant vector (ab) shows the displacement.
7

• Speed - the ratio of the distance (d) an object
  moves to the amount of time (t) the object moves
• Unit is meter per second (m/s)
• Vd/t
• Average speed computed for the entire duration
  of the trip
• Instantaneous speed measured at a particular
  instant
• Velocity (V) the speed and direction an object
  is moving.

8

• Graphing speed
• Distance on y-axis
• Time on x-axis
• Slope of Distance-Time graph tells me speed!
• Horizontal part tells me the object stop moving
• Curved parts tells me object is increasing and
  decreasing speed
• Straight portions tell me constant speed
• Greater the slope the higher the speed, vice versa

9
These are distance/time graphs. The green line
indicates fast, steady speed. The red line
indicates a steady speed, the object stopped, and
returning to the start. The blue line indicates
that the object is speeding up. (accelerating)
10

• Acceleration - rate at which velocity changes
• changes in speed
• changes in direction
• changes in speed and direction
• unit is meter per second per second(m/s2) Vf
  Vi or ?V
• t t
• ? Greek symbol delta, means change in
• Vf final velocity
• Vi initial velocity

11

• If velocity is increasing, then acceleration is
  positive.
• If velocity is decreasing, then acceleration is
  negative.

12

• Graphing acceleration
• Speed on y-axis
• Time on x-axis
• Slope of Speed-Time graph tells me acceleration!
• Horizontal part tells me object is at constant
  speed
• Slope downward tells me object is slowing down
  (decelerating)

13
Constant increasing acceleration, velocity is
increasing at a steady rate
Constant decreasing acceleration, velocity is
decreasing at a steady rate.
Car accelerates from rest, travels with a
constant velocity, accelerates to overtake then
drops back to the steady velocity before braking
to a halt
Acceleration increasing, velocity is increasing
at an increasing rate