Transcript ch. 5 and 6 - Cobb Learning

Measuring
Motion
What is
Force?
Friction
Gravity
Newton’s
Laws and
Momentum
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What is an object that
appears to stay in place
and helps you detect
motion in another
object called?
Reference Point
How do you calculate
average speed?
Distance ÷ Time
What is the difference
between speed and
velocity?
Velocity includes a
reference direction.
How do you calculate
average acceleration?
Final velocity – starting velocity
Time it takes to change velocity
What is the average
acceleration of a subway
train that speeds up from
9.6 m/s to 12 m/s in 0.8 s
on a straight section of
track?
3
2
m/s
Which of the following may
happen when an object
receives unbalanced forces?
a. The object changes direction
b. The object changes speed
c. The object starts to move
d. All of the above
d. All of the above
The combination of all
of the forces acting on
an object is the
______.
Net Force
A boy pulls a wagon with a
force of 6 N east as
another boy pushes it with
a force of 4 N east. What
is the net force?
10 N east
A dog pulls a rope with a
force of 10 N to the left as
another dog pulls with a
force of 12 N to the right.
What is the net force on
the rope?
2 N to the right
When finding net force,
why must you know
the directions of the
forces acting on an
object?
If you don’t know the
direction of the forces you
won’t know if you should
add the forces or subtract
them to find the net force.
Which is an example of
friction that is helpful?
a.
b.
c.
d.
car engine parts wearing out
tires moving a car forward
holes developing in your socks
the erosion of soil by wind
b. Tires moving a car
forward
When a mover puts furniture on
wheels, which type of friction is the
mover using to make the job easier?
a. static friction
b. sliding kinetic friction
c. rolling kinetic friction
d. gravitational friction
Rolling kinetic
friction
Why does friction
occur?
Microscopic hills and
valleys between two
touching surfaces stick
to each other.
What are the two
different types of
friction?
Kinetic and Static
Friction
Describe a situation in
which static friction is
useful.
Ex. When you’re
leaning against a table
you don’t want it to
slide out from under
you.
What is the acceleration
due to gravity?
9.8 m/s/s or 9.8
2
m/s
How do you calculate
the change in velocity
of a falling object?
∆v = g x t
Will air resistance have
more effect on the
acceleration of a falling
leaf or the acceleration of
a falling acorn?
Air resistance will have
more of an effect on
the acceleration of a
falling leaf.
What gives an object in
projectile motion its
vertical motion?
The force of gravity
pulling it toward the
surface of the earth.
A rock at rest falls off a tall
cliff and hits the valley
below after 3.5 s. What is
the rock’s velocity as it
hits the ground?
2
m/s
3.5 s x 9.8
= 34.3
m/s
What does Newton’s
first law of motion say
about objects at rest
and objects in motion?
Objects at rest stay at
rest and objects in
motion stay in motion
unless acted on by an
unbalanced force.
What is the relationship
between the force on
an object and the
object’s acceleration?
The acceleration of an
object increases as the
force exerted on the
object increases.
What force is
necessary to accelerate
a 70 kg object at a rate
2
of 4.2 m/s ?
F = 70 kg x 4.2
294 N
2
m/s
=
What does Newton’s
Third Law of Motion
state?
rd
3
Newton’s
Law:
Whenever one object
exerts a force on a second
object, the second object
exerts an equal and
opposite force on the first.
What is the momentum of
a 6 kg bowling ball that is
moving at 10 m/s down
the alley toward the pins?
p = 6 kg x 10 m/s down the
alley = 60 kg●m/s down the
alley