Transcript Chapter 8 Motion and Forces - Mrs. Cavanaugh's PbWiki

Chapter 8 Motion and Forces
SPEED
DESCRIBES HOW FAST AN OBJECT MOVES
How do you determine speed?
Take the distance traveled by an object and the time
it takes to travel that distance
SI UNIT FOR SPEED:
meters/second or m/s
What is constant speed?
When an object covers equal distance in
equal amounts of time
EQUATION
d÷t
What is the difference between
speed and velocity?
Velocity describes both speed and
direction
Velocity changes
if speed
or
direction
Change
Or both
d
v
t
Warm up problems
1.Anna swims exactly 220 m toward the shore
in 62 s. What is her velocity?
2.Daniel throws a baseball 32 m/s from third
to first base in 1.2 s. What is the distance
from first to third for the ball?
3. Bilal is an olympic skier who finished his
first 5.2 km race at an average velocity of 56
m/s downhill. What was his time in
seconds?
What is momentum
• Product of an object’s mass and its
velocity
What happens to the momentum as the
mass increases?
So does its momentum
What is the law of Conservation of
momentum?
The total amount of momentum in a
system is conserved.
Comparison of velocity and
momentum
Equation for momentum
p=m x v
P
M
V
Warm up problems for
momentum
1. Katara with a mass of 63.o kg runs with a
constant forward velocity of 1.50 m/s. What is
her momentum?
2. Ben hits a baseball with a momentum of 5.06
kg.m/s away from home plate after being hit.
The ball weighs 1.35 kg. What is the velocity
of the ball?
3. What is the mass of a toddler who is riding
in a car moving east at 89 km/h with a
momentum of 220 kg/m/s east.
What is acceleration?
Change in velocity divided by the time interval
in which the change occurs
What is the acceleration equation for straight
line motion?
acceleration = final velocity – initial velocity
time
Or
a = ∆v
t
Examples of Si units of
measurement that follow …….
Mass (m)= kg (g or lbs or ounces)
Distance (d)= m or km (miles, ft,
inches)
Time (t) = s or hr (minutes, days, yrs)
Velocity (v) = m/s or km/hr (ft/s, mph)
Momentum (p) = kg. m/s
Warm up problems for acceleration
1. Natalie accelerates her bike along a
straight path for 0 m/s to 4.0 m/s in 2.5 s.
Find her final acceleration
2. A cyclist travels at a constant velocity of
5.0 m/s westward, then speeds up with a
steady acceleration of 2.0 m/s2. Calculate
the cyclist speed after acceler. for 5.0 s.
3. A flowerpot falls off a second-story
windowsill with a velocity of 14.7 m/s. The
acceleration for this fall due to gravity is
9.8 m/s2. How long does it take for the pot
to hit the sidewalk?
What is Force?
The cause of acceleration or change in an
object’s velocity.
What is Net Force?
The combination of all
forces acting on an
object
•
How does force affect the motion of
an object?
force will cause on object to change its velocity or
acceleration.
Distinguish between balanced and
unbalanced forces?
Balanced forces: equal amount of force
exerted so net force is zero
No movement…..cancel each other
Unbalanced forces: forces acting on
object do not have same strength, so
greatest force will cause the object to
accelerate in that direction.
What is the difference between
balanced and unbalanced forces?
Balanced forces: equal amount of
force exerted so net force is zero
No movement…..cancel each other
Unbalanced forces: forces acting on
object do not have same strength,
so greatest force will cause the
object to accelerate in that
direction.
How does friction affect the motion
of an object?
unbalanced force that acts
against an objects direction
of motion
Also provides the force
needed to balance the force
of gravity on an object that
isn’t moving.
What is air resistance?
A form of friction that opposes an ojbects
motion
This is caused by the interaction between
the surface of a moving object and the
air molecules.
What affects air resistance
The size of the object
The shape of the object
Speed the object moves
What is gravity?
The attraction
between two
particles of matter
due to their mass.
What affects gravitational force?
• Mass and distance
• The greater the mass of an object=the larger
the gravitational force it exerts on the other.
• If the distance between two objects is
doubled, the gravitational force bewteen
them decreases to ¼ its original value
• If the distance is tripled, the gravitational
force decreases to o1/9 its original value
What are Newton’s three laws of
motion
1st law: an object at rest remains at
rest and an object in motion
mantains its velocity unless acted
upon by an unbalanced force
2nd law: The unbalanced force acting
on an object equals the object’s mass
times its acceleration
3rd law: For every action force, there is
an equal and opposite reaction force.