Download Chapter 9 Motion and Energy

Chapter 9 Motion and Energy
Chapter Preview Questions
1. Is a moving bus a good reference point from which to
measure your position?
a. No, because it is often late.
b. No, because it is not a stationary object.
c. Yes, because it is very large.
d. Yes, because it can travel very far.
Chapter 9 Motion and Energy
Chapter Preview Questions
1. Is a moving bus a good reference point from which to
measure your position?
a. No, because it is often late.
b. No, because it is not a stationary object.
c. Yes, because it is very large.
d. Yes, because it can travel very far.
Chapter 9 Motion and Energy
Chapter Preview Questions
2. To describe a friend’s position with respect to you, you
need to know
a. Your friend’s distance from you.
b. The direction your friend is facing.
c. Your friend’s distance and direction from you.
d. Your friend’s distance from a nearby object.
Chapter 9 Motion and Energy
Chapter Preview Questions
2. To describe a friend’s position with respect to you, you
need to know
a. Your friend’s distance from you.
b. The direction your friend is facing.
c. Your friend’s distance and direction from you.
d. Your friend’s distance from a nearby object.
Chapter 9 Motion and Energy
Chapter Preview Questions
3. Two cars traveling in the same direction pass you at
exactly the same time. The car that is going faster
a. moves farther in the same amount of time.
b. has more mass.
c. has the louder engine.
d. has less momentum.
Chapter 9 Motion and Energy
Chapter Preview Questions
3. Two cars traveling in the same direction pass you at
exactly the same time. The car that is going faster
a. moves farther in the same amount of time.
b. has more mass.
c. has the louder engine.
d. has less momentum.
Chapter 9 Motion and Energy
Chapter Preview Questions
4. To describe an object’s motion, you need to know its
a. position.
b. change in position.
c. distance.
d. change in position over time.
Chapter 9 Motion and Energy
Chapter Preview Questions
4. To describe an object’s motion, you need to know its
a. position.
b. change in position.
c. distance.
d. change in position over time.
Chapter 9 Motion and Energy
How can you describe an object’s motion?
You are in a stationary car
and another car passes you.
How would you describe the
motion of the other car?
Chapter 9 Motion and Energy
Section 1: Describing Motion
Standard 8.1.a Students know position
is defined in relation to some choice of a
standard reference point and a set of
reference directions.
Chapter 9 Motion and Energy
Section 1: Describing Motion
When is an object in
motion?
An object is in motion if it
changes position relative to a
reference point.
reference point
A place or object used for
comparison to determine if
something is in motion.
Chapter 9 Motion and Energy - Describing Motion
Relative Motion
Whether or not an
object is in motion
depends on the
reference point you
choose.
Chapter 9 Motion and Energy
Section 1: Describing Motion
What is the difference
between distance and
displacement?
vector
Distance is the total length of
the actual path between two
points. Displacement is the
length and direction of a
straight line between starting
and ending points.
A quantity that consists of both
a magnitude and a direction.
Chapter 9 Motion and Energy
Distance and Displacement
Section 1 Quick Quiz
When an object’s distance from another object is
changing,
A.it has a high velocity.
B.it is accelerating.
C.it is in motion.
D.it is moving at a constant speed.
Answer – C – it is in motion
Section 1 Quick Quiz
A place or object used for comparison to determine if
something is in motion is called
A.velocity.
B.a reference point.
C.a position.
D.a constant.
Answer – B – a reference point
Chapter 9 Motion and Energy
Section 2: Speed and Velocity
Standard 8.1.b Students know that average
speed is the total distance traveled divided by
the total time elapsed and that the speed of an
object along the path traveled can vary.
Standard 8.1.c Students know how to solve
problems involving distance, time, and average
speed.
Standard 8.1.d Students know the velocity of an
object must be described by specifying both the
direction and the speed of the object.
Chapter 9 Motion and Energy
Calculating Speed
How do you calculate
speed?
speed
To calculate the speed of an
object, divide the distance an
object travels by the amount of
time it takes to travel that
distance.
The distance an object travels
per unit of time.
Speed = Distance
Time
Chapter 9 Motion and Energy
Calculating Speed
If a distance runner runs
10 miles in one hour,
what is her speed?
The runner’s speed is 10 miles
per hour.
Speed = 10 miles
1 hour
Instantaneous speed
The rate at which an object is
moving at a given instant in
time.
Chapter 9 Motion and Energy
Calculating Speed
How do you calculate
average speed?
A cyclist travels 32
kilometers during the
first 2 hours. Then he
travels 13 kilometers
during the next hour.
What is his average
speed?
To calculate average speed (v),
divide the total distance
traveled (d) by the total time (t).
Average Speed = Total Distance
(v)
Total Time
v = 32 km + 13 km = 45 km
2h+1h
=3h
v = 15 km/h
Chapter 9 Motion and Energy
Velocity
How can you describe
changes in velocity?
Changes in velocity may be due
to changes in speed, changes in
direction, or both.
•Like displacement, velocity is a
vector.
•It has magnitude and direction.
A jet airplane’s velocity could
be described as 700 miles per
hour to the east.
Chapter 9 Motion and Energy
Graphing Speed
How can you interpret
graphs of distance
versus time?
The slope of a distance-versustime graph represents speed,
that is, the rate that distance
changes in relation to time.
• Time is shown on the
horizontal axis, or x-axis.
• Distance, or position, is shown
on the vertical axis, or y-axis.
• A point on the line represents
the distance an object has
traveled from the origin or a
reference point at a particular
time.
Chapter 9 Motion and Energy
Graphing Motion
You can use distance-versus-time graphs to interpret motion.
Section 2 Quick Quiz
Speed equals distance divided by
A.size.
B.time.
C.velocity.
D.motion.
Answer – B - time
Section 2 Quick Quiz
When you know both the speed and direction of an
object’s motion, you know the
A.velocity of the object.
B.distance the object has traveled.
C.acceleration of the object.
D.average speed of the object.
Answer – A – velocity of the object
Section 2 Quick Quiz
Average speed is
A.equivalent to velocity.
B.the total distance traveled divided by the total time.
C.the rate at which an object is moving at a given
instant.
D.the rate at which a slope changes.
Answer – B – the total distance traveled divided by the
total time
Section 2 Quick Quiz
If the speed of an object does NOT change, the object
is traveling at a
A.increasing speed.
B.decreasing speed.
C.constant speed.
D.average speed.
Answer – C – constant speed
Section 2 Quick Quiz
If a bicyclist travels 32 miles in 4 hours, her average
speed is
A.8 mi/h.
B.4 mi/h.
C.16 mi/h.
D. 128 mi/h.
Answer – A – 8 mi/h
Section 2 Quick Quiz
If an object moves in the same direction and at a
constant speed for 8 hours, which of the following is
true?
A.The object accelerated during the 8 hours.
B.The object decelerated during the 8 hours.
C.The object’s speed changed during the 8 hours.
D.The object’s velocity did not change.
Answer – D – The object’s velocity did not change.
Section 2 Quick Quiz
If you know a car traveled 250 miles in 5 hours, you can
find its
A.direction.
B.average speed.
C.velocity.
D.acceleration.
Answer – B – average speed
Section 2 Quick Quiz
A car travels 100 km in the first hour of a trip. The car
continues to travel for 4 more hours and travels 350 km.
What was the average speed of the car for the trip:
A.95 km/h.
B.88 km/h.
C.90 km/h.
D.111 km/h.
Answer – C – 90 km/h
Section 2 Quick Quiz
In a graph of distance versus time, the slope represents
A.speed.
B.acceleration.
C.potential energy.
D.displacement.
Answer – A - speed
Section 2 Quick Quiz
The rise of a line on a distance-versus-time graph is
600 km and the run is 30 hours. What is the speed of
the object represented by this graph?
A.200 km/h
B.450 km/h
C.20 km/h
D.1800 km/h
Answer – C – 20 km/h
Chapter 9 Motion and Energy
Section 3: Acceleration
Standard 8.1.e Students know changes in
velocity may be due to changes in speed,
direction, or both.
Standard 8.1.f Students know how to interpret
graphs of position versus time and graphs of
speed versus time for motion in a single
direction.
Chapter 9 Motion and Energy
Changing Velocity
What kind of motion
does acceleration refer
to?
In science, acceleration refers
to increasing speed, decreasing
speed, or changing direction.
Just as objects can speed up,
they can also slow down. This
change in speed is sometimes
called deceleration, or negative
acceleration.
An object that is traveling at a
constant speed can be
accelerating if it is changing
direction.
Chapter 9 Motion and Energy
Changing Velocity
How do you calculate
acceleration?
To determine the acceleration of
an object, you must calculate its
change in velocity per unit of
time.
Acceleration = Final Velocity – Initial Velocity
Time
Chapter 9 Motion and Energy
Calculating Acceleration
To determine the acceleration of an object, you must
calculate its change in velocity per unit of time.
Chapter 9 Motion and Energy
Calculating Acceleration
As a roller-coaster car starts down a slope, its velocity is 4 m/s. But
3 seconds later, its velocity is 22 m/s in the same direction. What is
its acceleration?
Read and Understand
What information have you been given?
Initial velocity = 4 m/s
Final velocity = 22 m/s
Time = 3 s
Chapter 9 Motion and Energy
Calculating Acceleration
As a roller-coaster car starts down a slope, its velocity is 4 m/s. But
3 seconds later, its velocity is 22 m/s in the same direction. What is
its acceleration?
Plan and Solve
What quantity are you trying to calculate?
The acceleration of the roller-coaster car = __
What formula contains the given quantities and the unknown
quantity?
Acceleration = (Final velocity - Initial velocity)/Time
Perform the calculation.
Acceleration = (22 m/s - 4 m/s)/3 s = 18 m/s/3 s
Acceleration = 6 m/s2
The acceleration is 6 m/s2 down the slope .
Chapter 9 Motion and Energy
Calculating Acceleration
As a roller-coaster car starts down a slope, its velocity is 4 m/s. But
3 seconds later, its velocity is 22 m/s in the same direction. What is
its acceleration?
Look Back and Check
Does your answer make sense?
The answer is reasonable. If the car’s velocity increases by 6 m/s
each second, its velocity will be 10 m/s after 1 second, 16 m/s after
2 seconds, and 22 m/s after 3 seconds.
Chapter 9 Motion and Energy
Calculating Acceleration
Practice Problem
A falling raindrop accelerates from 10 m/s to 30 m/s in 2
seconds. What is the raindrop’s acceleration?
(30 m/s - 10 m/s) ÷ 2 seconds = 10 m/s2
Chapter 9 Motion and Energy
Calculating Acceleration
Practice Problem
A certain car can accelerate from rest to 27 m/s in 9
seconds. Find the car’s acceleration.
(27 m/s - 0 m/s) ÷ 9 s = 27 m/s ÷ 9 s = 3 m/s2
Chapter 9 Motion and Energy
Graphing Acceleration
You can use both a speed-versus-time graph and a distanceversus-time graph to analyze the motion of an accelerating
object.
Section 3 Quick Quiz
Which of these is an example of deceleration?
A.a car moving after a green light
B.a train coming in to its station
C.a roller coaster moving down a steep hill
D.an airplane following a straight flight path
Answer – B – a train coming in to its station
Section 3 Quick Quiz
The moon accelerates because it is
A.in a vacuum in space.
B.a very large sphere.
C.continuously changing direction.
D.constantly increasing its speed and orbit.
Answer – C – continuously changing direction
Section 3 Quick Quiz
If speed is measured in kilometers per hour and time is
measured in hours, the unit of acceleration is
A.kilometers.
B.kilometers per hour per hour.
C.kilometers per hour.
D.hours.
Answer – B – kilometers per hour per hour
Section 3 Quick Quiz
Which of the following is the correct equation for
acceleration?
A.acceleration = (final speed – initial speed)/time
B.acceleration = (final speed – initial speed) x time
C.acceleration = time/(final speed – initial speed)
D.acceleration = (initial speed – final speed)/time
Answer – A - acceleration = (final speed – initial
speed)/time
Section 3 Quick Quiz
In a graph showing speed versus time, a straight line
shows the acceleration is
A.decreasing.
B.increasing.
C.changing.
D.constant.
Answer – D - constant
Chapter 9 Motion and Energy
Section 4: Energy
Standard 8 Framework Students should begin
to grasp four concepts that help to unify
physical sciences: force and energy; the laws
of conservation;…
Chapter 9 Motion and Energy
Kinetic Energy
What factors affect an
object’s kinetic energy
and potential energy?
The kinetic energy of an object
depends on both its mass and
its speed.
Kinetic energy increases as
mass increases.
Kinetic energy also increases
when speed increases.
Kinetic Energy = ½ x Mass x Speed2
Chapter 9 Motion and Energy
Kinetic Energy
Kinetic energy increases as mass and speed increase.
Chapter 9 Motion and Energy
Exponents
An exponent tells how many times a number is used as a factor. For
example, 3 x 3 can be written as 32. You read this number as “three
squared.” In the formula for kinetic energy, speed is squared. For
example, you can calculate the kinetic energy of a 70-kg person moving at
a speed of 2 m/s by using the formula below.
KE = ½ x Mass x Speed2
= ½ x 70 kg x (2 m/s) 2
= 140 kg•m2/s2 or 140 joules.
Note:
1 kg•m2/s2 = 1 joule
Chapter 9 Motion and Energy
Exponents
Practice Problem
What is the kinetic energy of a 30-kg rock moving at a speed
of 10 m/s?
1,500 joules
Chapter 9 Motion and Energy
Potential Energy
potential energy
Stored energy that results from
the position or shape of an
object.
Chapter 9 Motion and Energy
Potential Energy
Gravitational potential energy increases as weight and height
increase.
Chapter 9 Motion and Energy
Transformations Between
Potential and Kinetic Energy
A pendulum continuously transforms energy from kinetic to
potential energy and back.
Section 4 Quick Quiz
The energy associated with motion is called
A.elastic potential energy.
B.gravitational potential energy.
C.nuclear energy.
D.kinetic energy.
Answer – D – kinetic energy
Section 4 Quick Quiz
Which of the following has kinetic energy?
A.a rock poised for a fall
B.an archer’s bow that is drawn back
C.a boat going downstream
D.a car waiting at a red light
Answer – C – a boat going downstream
Section 4 Quick Quiz
Potential energy that depends on height is called
A.mechanical energy.
B.elastic potential energy.
C.kinetic energy.
D.gravitational potential energy.
Answer – D – gravitational potential energy