Transcript CHAPTER 8

CHAPTER 8
MOTION AND FORCES
8.1 MOTION
SPEED • 65 mi/hr
CONSTANT SPEED TIME
DISTANCE
0
0
1
15
2
30
3
45
4
?
AVERAGE SPEED SPEED = DISTANCE / TIME
(v = d/t )
TIME
DISTANCE
1
2
3
5
20
100
AVERAGE
20
25
Graphing Speed
• What does a
straight line
indicate about the
speed?
• What does the
slope of a line
indicate?
• Draw another line
showing speed that
is changing.
CHECKER AUTO PARTS 500
• http://www.nascar.com
/
• SPEED = DISTANCE
TIME
DISTANCE = 315 laps
TIME = 3 hours
SPEED = ?
Track length = 1 mile
VELOCITY • The speed of these racers
may not have
changed…Explain why
their velocity has changed.
• List some examples of how
change of direction may be
stated:
– North, south, east, west
– 280 degrees (on a compass)
– Up, down…
MOMENTUM • Momentum = mass x
velocity
( p = mv )
How does mass influence
momentum?
How does speed influence
momentum?
SUMMARY
MOTION
SPEED
VELOCITY
MOMENTUM
DISTANCE and TIME
SPEED and DIRECTION
VELOCITY and MASS
8.2 ACCELERATION AND
FORCE
ACCELERATION –
ACCELERATION = FINAL VELOCITY – INITIAL VELOCITY
TIME
What evidence of acceleration
do you see in these pictures?
(read page 260)
boat speeding up
car slowing down
ACCELERATION (continued)
What evidence of acceleration can be
seen in this picture?
(changing direction)
ZERO ACCELLERATION •
Identify two conditions that
must be met for these joggers to
be at zero acceleration.
(page 261)
1. No change of direction.
2. No change (increase/decrease)
in speed.
FORCE –
IS THE CAUSE OF ACCELERATION
• Examples of FORCES:
– Gravity
– Engines
– Rubber band
–
• BALANCED FORCES do not
change motion.
• UNBALANCED FORCES
change motion.
FRICTION A. SURFACE FRICTION –
depends on roughness of surface.
Ways to INCREASE friction:
1. Sandpaper
2.
Ways to DECREASE friction:
1. Oil
2.
FRICTION (continued )
B. AIR FRICTION (resistance)
- depends on the size,
shape, or speed of an object.
Ways to INCREASE
friction:
1. Larger surface area
2.
Ways to DECREASE
friction:
1. Smaller surface area.
2.
GRAVITY • Gravity is exerted by all
objects on each other.
• Depends on mass of
objects.
– MORE mass = MORE
gravity
• Depends on distance
between objects.
– MORE distance = LESS
gravity
Which law of gravitational attraction
is illustrated by this cartoon?
8.3 NEWTON’S LAWS OF
MOTION
WEIGHT Is the gravitational force an object
experiences due to its mass.
Is dependent on ones’ location.
May be described in an equation:
weight = mass x free-fall acceleration( g
= 9.8 m/s2 )
The metric unit of measurement is the
NEWTON and is measured with a
SPRING SCALE.
MASS Is a measure of the amount of matter in an object.
Is not dependent on location.
The metric unit of measurement is the GRAM and is
measured with a BALANCE.
FIRST LAW ( INERTIA) Objects at rest stay at rest and
objects in motion stay in
motion unless an unbalanced
force acts on them.
(This law describes what
happens when forces on an
object are BALANCED and
the net force is zero.)
EXAMPLES:
SECOND LAW (ACCELERATION) A. This law describes the relationship between force,
mass, and acceleration and may be stated as an
equation:
force = mass x acceleration
( f = ma )
• (This law describes what happens when forces on an
object are UNBALANCED and the net force is not
zero.)
B. Acceleration and
EQUAL FORCE • When the forces are
equal, less massive
objects accelerate
faster than more
massive ones.
• EXAMPLES:
C. Acceleration and
EQUAL MASS • When the masses are
equal, a greater force
provides greater
acceleration.
• EXAMPLES:
FREE FALL • When gravity is the
accelerating force.
• Acceleration due to gravity is
9.8 m/s/s ( g = 9.8 m/s2 )
• Gravity accelerates all objects
at the same rate!
Acceleration due to GRAVITY
TERMINAL VELOCITY • Force of air resistance
equals
the gravitational force
(weight)
Object stops accelerating
Terminal velocity for a
human body is about
200 mph.
TERMINAL VELOCITY
and AMUSEMENT PARKS
• New ride at Wisconsin
Dells – Terminal
Velocity.
• 100 foot free fall drop
• 70 mph
• 140 foot tower
• $40 first time…$25
second time
THIRD LAW (ACTION = REACTION)
• Every action force has
an equal and opposite
reaction force
• FxD=fxd
– (action = reaction)
• EXAMPLES:
THE THIRD LAW AND
• Unbalanced forces inside
the engine compartment
allow a rocket to move.
ROCKETS
Newtons Laws of Motion
First Law
Second Law
Third Law
INERTIA
ACCLERATION
ACTION = REACTION
BALANCED FORCES
UNBALANCED FORCES
FORCES ACT IN PAIRS
STUDY FOR THE TEST
• VOCABULARY
• SPEED / VELOCITY / ACCELERATION
• IS IT A BALANCED OR UNBALANCED
FORCE
• 1ST, 2ND, OR 3RD LAW EXAMPLES
• THE MOTION LABS