Motion Unit

1
Motion Unit

• Chapter 10

2
Measuring Motion

• Motion is the change in an objects position.
• Reference point is a stationary object that is
  used to compare an objects motion.
• Displacement is the change in position of an
  object.
• Straight line.
• Must be in a particular direction.

3
Speed

• Speed is how fast an object moves.
• v d t
• Common unit for measuring speed is m/s
• distance
• time
• Speed is illustrated in a distance-time graph.
• Time on the x-axis
• Distance on the y-axis
• Horizontal line indicates that the object is not
  moving.

4
Types of Speed

• Constant speed is speed that does not change.
• Average speed is the distance traveled by an
  object divided by the time the object takes to
  travel that distance.
• Instantaneous speed is speed measured in an
  infinitely small time interval.

5
Velocity

• Velocity is speed and direction.
• Common unit for velocity is m/s north
• distance
• time
• direction

6
Acceleration

• Chapter 10, section 2.

7
Acceleration is the rate at which velocity
changes over time

• Speed changes
• Increasing
• Decreasing
• Direction changes
• If you travel in a circle at a constant speed,
  youre accelerating because you are constantly
  changing directions.

8
Centripetal Acceleration

• Centripetal acceleration is the acceleration that
  occurs in uniform circular motion

9
Calculating Acceleration

• acceleration vfinal-vinitial/time or a ?v/t
• Small acceleration, velocity is increasing very
  gradually
• Large acceleration, velocity is increasing more
  rapidly
• Positive acceleration always means a the objects
  velocity is always increasing

10
Negative Acceleration

• Negative acceleration means the objects velocity
  is decreasing

11
Graphing acceleration

• Plot the time on the x-axis
• Plot the velocity on the y-axis
• A straight line indicates positive acceleration
• Positive slope represents speeding up
• Negative slope represents slowing down
• Slope is zero if the acceleration is zero

12
Balanced and unbalanced forces

• A force is an action exerted on a body in order
  to change the bodys state of rest or motion
• A force has a magnitude and direction
• The net force is the combination of all of the
  forces acting on the object
• The object accelerates in the direction of the
  net force.
• The object will not accelerate if the net force
  is zero.

13
Balanced and unbalanced forces

• Balance forces do not cause an object at rest to
  start moving
• Net forces are zero
• Unbalanced forces cause the object to move in the
  direction of the greater force
• Net forces are greater than zero

14
Force of friction

• Friction is a force that opposes motion between
  two surfaces that are in contact
• The rougher the surface, the greater the friction
• Static friction is the force that resists the
  initiation of sliding motion between two surfaces
  that are in contact and at rest

15
Force of friction

• Kinetic friction is the force that opposes the
  movement of two surfaces that are in contact and
  are sliding over each other
• Sliding friction occurs when objects pass each
  other
• Rolling friction occurs when a round object rolls
  over a flat surface

16
Force of friction

• Static friction is usually greater than kinetic
  friction
• Fluid friction is the friction between air and
  the surface of the moving object
• Air is displaced as an object moves
• Air resistance increases as the speed of the
  object increases
• Designing a shape of a car to displace less air
  is called streamlining

17
Friction and motion

• Friction is necessary, but sometimes harmful
• Friction can be reduced by lubricants
• Friction can be increased by making surfaces
  rougher
• Hydroplaning occurs when water is trapped between
  the tires of a car and the road.

18
Review Questions

• What do you call a stationary object that is used
  for a comparison to detect motion?
• (reference point or reference frame)
• What do you call the distance between the
  starting point to the final destination?
• (displacement)
• What describes how fast an object moves?
• (speed)
• What is the type of speed when equal distances
  are covered in equal time?
• (constant speed)
• What is graphed on the x-axis of a speed graph?
• (time)
• What is graphed on the y-axis of a speed graph?
• (distance)

19
Review Questions

• What do you call the total distance the object
  traveled divided by the total time it took for
  the object to move that distance?
• (average speed)
• What is speed measured in infinitely small time
  intervals?
• (instantaneous speed)
• What do you call speed with direction?
• (velocity)
• What is the formula for calculating speed?
• (v d/t)
• What is the formula for calculating acceleration?
• (a (vf vi)/t
• What do we call the rate in change of velocity?
• (acceleration)

20
Review Questions

• What do we graph on the y-axis of an acceleration
  graph?
• (speed)
• What type of forces causes change in motion of an
  object?
• (unbalanced forces)
• What type of forces causes no change in the
  motion of an object?
• (balanced forces)
• What is a force?
• (a push or pull)
• What do we call the force that resist a surface
  moving over another surface?
• (friction)
• What is the type of friction where everything is
  stationary?
• (static friction)

21
Review Questions

• What type of friction involve moving objects?
• (kinetic friction)
• What are the two types of kinetic friction?
• (sliding friction rolling friction)
• What type of friction is air resistance?
• (fluid friction)
• What reduces friction?
• (lubricants)

22
Review Questions
23
Review Questions
24
Review Questions