Transcript Motion

Motion
Describing Motion
Motion
Occurs when an
object changes
position
Don’t have to
see to know
that it occurs
Motion
Motion can be
describe by
Speed, Velocity,
Acceleration of
an object.
Frame of Reference
Stationary (Not Moving)
Reference Point
Starting place
(where the zero value is)
Frame of Reference
Examples
Earth
Most common
frame of
reference
Tree
House
Stars
Frame of Reference
Teacher Domain
http://www.teachersdomain.org/resource/
lsps07.sci.phys.fund.frameref/
Distance
How far an
object has
moved
Displacement
Distance and
Direction of an
objects change
in position from
the starting point
to ending point.
Displacement
Flash Interactive
http://www.upscale.utoronto.ca/GeneralI
nterest/Harrison/Flash/ClassMechanics/
DisplaceDistance/DisplaceDistance.html
Distance and Displacement
A physics teacher
walks 4 meters East,
2 meters South, 4
meters West, and
finally 2 meters
North.
Distance and Displacement
 A physics teacher walks 4 meters
East, 2 meters South, 4 meters West,
.
1. What is the total
distance?
2. What is the
displacement?
and finally 2 meters North
Displacement
1. What is the displacement of the crosscountry team if they begin at the school,
run 10 miles and finish back at the
school?
Answer: zero because the displacement is
measured from the starting to ending
point.
Displacement and Distance
A student walks 3 blocks south, 4 blocks west,
and 3 blocks north. What is the displacement of
the student?
1. 10 blocks east
2. 10 blocks west
3. 4 blocks east
4. 4 blocks west
3 blocks north
Answer: 4 blocks west
3 blocks south
4 blocks west
Quick Review
1. A moving object passes a still object.
Which one is the frame of reference
moving or still object?
2. The ______ from point A to point B is
5 cm.
Rates
Rate – any change
over time
Different Rates
Speed/Velocity
Acceleration
Speed
Speed - The distance an object travels
per unit of time.
Rate – any change over time
distance
speed = time
d
s=
t
Types of
SPEEDS
Constant
Speed stays the same
Average
Total distance traveled divided by the
total time traveled
Instantaneous
Speed at a given point in time
Velocity
Speed in a given
direction
d
v
distance
velocity =
time
d
v=
t
t
Graphing Motion
Figure 1
Speed vs.
Velocity
Figure 2
Quick Write:
Which one of the
following figures
shows the car slowing
down? Explain why?
Speed vs. Velocity
Quick Write
1.
2.
The speed and direction in which an object is moving
is called?
What is the formula for velocity?
Example of Speed:
If a frog jumps a distance of 3 m in 6
seconds, what is its speed?
d = 3 m t = 6 sec
v =
d
t
v=?
v = 3 m / 6 sec = 0.5 m/sec
Example:
A toad jumped 3 km in 1 hour,
then jumped 1 km in 2 hours,
it rested for 1 hour,
and then jumped 5 km in 2 hours.
What was the toad’s average speed?
d = 3 km + 1 km + 5 km = 9 km
t = 1 hr + 2 hr + 1 hr + 2 hr = 6 hr
d
v =
v=?
t
v = (9 km) / (6 hr) = 1.5 km/hr
NOTE: The time the toad stopped is included in the
total time.
Average
Speed
d
v
t
A runner completed the 100.-meter dash in 10.0
seconds. Her average speed was
1. 0.100 m/s
2. 10.0 m/s
3. 100. m/s
4. 1,000 m/s
Answer: 10 m/s because v= d = 100m =10m/s
t
10s
Instantaneous Velocity
 Which of the follow sentences contains an
example of instantaneous velocity?
(A) “The car covered 500 kilometers in the first
10 hours of its northward journey.”
(B) “Five seconds into the launch, the rocket was
shooting upward at 5000 meters per second.”
(C) “The cheetah can run at 70 miles per hour.”
(D) “Moving at five kilometers per hour, it will
take us eight hours to get to the base camp.”
(E) “Roger Bannister was the first person to run
one mile in less than four minutes.”
Speed Practice Problems
1. What is the speed of a car that travels
180 km in 1.5 hours?
2.What is the average speed of a dog cart that
travels 2 km in the first 30 min., 0.5 km in the
next hour and 3 km in 30 min.?
3.If a car has a constant velocity of 80 km/hr,
how far will it travel in 5.5 hr?
4.If you walk at a speed of 2 km/hr, how long
will it take you to walk 18.8 km?
5.If a lion runs 40 km/hr for 120 min, how far
will it travel?
6.The train was traveling west at 200 km/hr.
How long will it take the train to go 3600 km?
Brain Pop Movie
Acceleration
http://glencoe.mcgrawhill.com/sites/0078802482/student_vie
w0/brainpop_movies.html#
Acceleration
The rate of change
of velocity
velocity
acceleration = time
v
a= t
vf - vi
a= t
Δv
a = Δt
Δ v = vf - vi
Δ v = change in velocity
vf = final velocity
vi = initial velocity
Units
m/sec
m/sec
m/sec
Δ t = tf - ti
Units
t = time interval
tf = final time
ti = initial time
sec
sec
sec
Types of Accelerations
Constant
Acceleration stays the same
Average
Total velocity divided by the total time
Instantaneous
Acceleration at a given point in time
Graphing Motion
Example of
Acceleration
v
a
t
A runner accelerates to a speed of 8.0 meters
per seconds in 4.0 seconds. What was her
acceleration?
1. 0.50 m/s2
2. 2.0 m/s2
3. 9.8 m/s2
4. 32 m/s2
Answer: 2.0 m/s2 because a=v = 8m/s = 2 m/s2
t
4s
Example: What was the acceleration of a car that
went from 0 kph to 90 kph in 60 seconds?
a=
v
t
Δ v = vf - vi
a=?
vf = 90 kph vi = 0 kph
t = 60 sec = 1 min = 1/60 hr
Δv = 90 kph - 0 kph = 90 kph
a = (90kph) / (1/60 hr) = 5400 km/hr2
NOTE:
90 ÷ 1 = 90 x 60 = 5400
60
Acceleration Practice Problems
1.How long will it take a car to accelerate from
30 m/s to 90 m/s at a rate of 4 m/s2 ?
2.A truck is traveling at 90 kph suddenly slams on it
brakes. After braking for 2 minutes, the truck
reaches a speed of 30 kph. What is the trucks
acceleration?
3.What is the change in velocity of a car that
accelerates at 60 km/hr2 for 0.25 hr?
4. What is the final velocity of a truck that
accelerated at 40 m/sec2 for 60 sec and has
and initial speed of 30 m/sec?
5.How long will it take a skateboard traveling at
25 m/sec to stop if it accelerates at -4 m/sec2?
6.What is the acceleration of a ball that goes
from 0 m/sec to 60 m/sec in 15 seconds?
Force
Push or pull that
one body exerts on
another
A force can cause
an object to move
Different Types of Forces
Net Force=(Total Force)
Resulting combination of all forces acting
on an object
Balanced Forces (Equal Forces)
Forces that are equal in size and opposite
in direction
Unbalanced Forces (Unequal Forces)
Forces that are NOT equal in size or
opposite in direction
ALWAYS cause a change in motion
Quick Write
What are the three different
types of forces? Define each
forces.
F= ma
F
Force
Calculating force
F=ma
F = force
m = mass
a = acceleration
Units
kg·m/sec2 or N
kg
m/sec2
NOTE: one Newton (N) equal one kilogram
meter per second squared.
m
a
Friction
Friction is an opposing (opposite) force
in the direction in which the object is
moving.
Types of Friction
Static=not moving
Sliding
Rolling
Fluid
Example
How much force is exerted by a 2 kg
baseball that is accelerating at 400
m/sec2?
F = ? m = 2 kg a = 400 m/sec2
F=ma
F = (2 kg)(400m/sec2)
= 800 kg × m/sec2 = 800 N
Force Practice Problems
1. A 3 kg baseball accelerates at 250 m/sec2.
How much force is it exerting?
2. A 15 kg coconut hit the sand with 220
kg*m/sec2 force. What was the
coconut’s acceleration?
3. 2900 N force is exerted by a truck on a
compact car. If the truck has an
acceleration of 2 m/sec2, what is the
mass of the truck?
4. A car with a mass of 1000 kg accelerates
through a green light at 4 m/s2. What is
the net force on the car?
5. A person pushes a rock across the
ground with a force of 60 N. The rock
has a mass of 40 kg, what is the
acceleration of the rock?
Newton’s Laws of Motion
1st Law (Law of inertia)
An object moving at
constant velocity keeps
moving at that velocity
unless a net force acts on
it
V=20m/s
V=10m/s
F=10N
Newton’s Laws of Motion
I. Newton’s First Law of Motion
An object in motion remains in motion.
An object at rest remains at rest.
Also known as the Law of Inertia
Inertia
The tendency of an object to resist any change in
its motion
Law of Inertia
An object in motion will remain in motion unless
acted on by an outside force
An object at rest will remain at rest unless acted
on by an outside force
Newton’s Law of Motion
2nd Law (F=ma)
The net force acting on an object causes the
object to accelerate in the direction of the net
force
3rd Law
For every action there is an equal but
opposite reaction
Brain Pop Movie
Newton’s Three Laws
http://glencoe.mcgrawhill.com/sites/0078802482/student_vie
w0/brainpop_movies.html#
Gravity
Gravity a force between two objects.
Gravity causes an object to accelerate
towards Earth.
Weight
Force of gravity acting on an object
W=m*g
W=kg*m/s2
Quick Write
Name Newton’s Three Law’s of
Motion.
Calculating weight
F = mg
w
Fw
m g
FW = m g
FW = weight
m = mass
g = acceleration due to gravity
Units
N or kg · m/sec2
kg
m/sec2
NOTE: The acceleration due to gravity on Earth is 9.8
m/sec2.
Example:
What is the weight of a 100 kg man on Earth?
FW = m g
FW = ?
m = 100 kg
g = 9.8 m/sec2
FW = (100 kg)(9.8 m/sec2)
= 980 kg m/sec2 = 980 N
1. What is the weight of a 22 kg object on
Earth?
2. An apple drops from the tree with a
mass of 112kg. What is the weight of the
apple?
3. If an astronaut has a mass of 100kg,
what is his weight on Earth where the
acceleration due to gravity is 9.8m/s2.
4. An object on Earth is moving with a
weight of 10 N, what is the mass of the
object?
5. If an astronaut with a mass of 88kg
weighs how much in kg*m/s2.
Momentum
1. Relates to the amount of energy an
object has.
2. Relates to the force needed to stop an
object.
3. Depends on the mass and velocity of the
object.
Calculating momentum
p= mv
p
p=mv
Units
p = momentum
m = mass
v = velocity
m
kg × m/sec
kg
m/sec
NOTE: Units can vary.
v
Example:
What is the momentum of a 1000 kg car goin 90
km/hr?
p=mv
p=?
1000 kg
v = 90 km/hr
1 hr = 60 min
1 min = 60 sec
1 km = 1000 m
p = (1000 kg)(90 km/hr)(1 hr/60 min)
sec)(1000 m/1 km)
= 25000 kg m/sec
m=
(1 min/60