All matter in the universe is constantly in motion, from the revolution of Earth around the Sun to elections moving around the nucleus of an atom.

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Chapter 10

• Section 1

2
What is Motion?
1
Matter and Motion

• All matter in the universe is constantly in
  motion, from the revolution of Earth around the
  Sun to elections moving around the nucleus of an
  atom.

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What is Motion?
1
Changing Position

• Something is in motion if it is changing
  position.

• It could be a fast-moving airplane, a leaf
  swirling in the wind, or water tricking from a
  hose.

• When an object moves from one location to
  another, it is changing position.

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What is Motion?
1
Changing Position

• The runners sprint from the start line to the
  finish line.

• Their positions change, so they are in motion.

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What is Motion?
1
Relative Motion

• An object changes position if it moves relative
  to a reference point.

• Picture yourself competing in a 100-m dash.

• You begin just behind the start line.

• When you pass the finish line, you are 100 m from
  start line.

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What is Motion?
1
Relative Motion

• If the start line is your reference point, then
  your position has changed by 100 m relative to
  the start line, and motion has occurred.

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What is Motion?
1
Distance and Displacement

• Displacement includes the distance between the
  starting and ending points and the direction in
  which you travel.

• This figure shows the difference between distance
  and displacement.

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What is Motion?
1
Speed

• Speed is the distance traveled divided by the
  time taken to travel the distance.

• Speed can be calculated from this equation

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What is Motion?
1
Speed

• In SI units, distance is measured in m (meters)
  and time is measured in s (seconds).

• As a result, the SI unit of speed is the m/sthe
  SI distance unit divided by the SI time unit.

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What is Motion?
1
Average Speed

• Average speed is found by dividing the total
  distance traveled by the time taken.

• An object in motion can change speeds many times
  as it speeds up or slows down.

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What is Motion?
1
Average Speed

• The speed of an object at one instant of time is
  the object's instantaneous speed.

• If it takes you 0.5 h to walk 2 km to the
  library, your average speed would be as follows

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What is Motion?
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Average Speed

• Average speed, instantaneous speed, and constant
  speed are illustrated here.

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What is Motion?
1
Graphing Motion

• You can represent the motion of an object with a
  distance-time graph.

• For this type of graph, time is plotted on the
  horizontal axis, and distance is plotted on the
  vertical axis.

Click box to view movie.
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What is Motion?
1
Distance-Time Graphs and Speed

• Look at the graph.

• According to the graph, after 1 s student A
  traveled 1 m.

• Student B, however, traveled only 0.5 m in the
  first second.

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What is Motion?
1
Distance-Time Graphs and Speed

• So student A traveled faster than student B.

• The line representing the motion of student A is
  steeper than the line for student B.

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What is Motion?
1
Distance-Time Graphs and Speed

• A steeper line on the distance-time graph
  represents a greater speed.

• A horizontal line on the distance-time graph
  means that no change in position occurs.

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What is Motion?
1
Velocity

• If you are hiking in the woods, you want to know
  not only your speed, but also the direction in
  which you are moving.

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What is Motion?
1
Velocity

• The velocity of an object is the speed of the
  object and direction of its motion.

• This is why a compass and a map are useful to
  hikers.

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What is Motion?
1
Velocity

• Velocity has the same units as speed, but it also
  includes the direction of motion.

• The velocity of an object can change if the
  object's speed changes, its direction of motion
  changes, or they both change.

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Section Check
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Question 1
To determine whether something has changed
position, you need a _______.
A. compass B. global positioning system C. map D.
reference point
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Section Check
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Answer
The answer is D. If someone starts a car and
drives it 100 meters from its parking spot, the
parking spot can be used as a point of reference
to show that the car moved.
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Section Check
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Question 2
Displacement includes your _______ and _______ as
well as the _______ in which you have traveled.
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Section Check
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Answer
It includes your starting point, ending point,
and direction in which you have traveled. It is
possible to have traveled a great distance and
still have a displacement of zero if you traveled
in an enormous circle and ended right where you
began.
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Section Check
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Question 3
Speed equals distance divided by _______.
A. force B. mass C. time D. velocity
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Section Check
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Answer
The answer is C. The smaller the t value in
sd/t, the greater the speed.