Download Chapter 4 Motion

Lesson 1
What Factors Affect Motion?
Fast Fact
Giant Tops This spinning-ring ride seems to defy gravity when it's moving. Carnival
rides like this one are based on NASA training equipment. An astronaut trainee can
turn in all directions: up and down, left and right, and sideways. In the Investigate,
you will observe the way an air bubble moves when you apply force from different
directions.
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Changes in Motion
Materials
 clear, l-L plastic bottle with cap
 water
 small piece of soap
Procedure
1. Fill the bottle with water, but leave just enough space for a small air bubble. Add a
small piece of soap. Cap the bottle tightly.
2. Lay the bottle on its side on a flat surface. You should see one small bubble in the
bottle. Hold the bottle steady until the bubble moves to the center of the bottle and
stays there.
3. Predict what will happen to the air bubble if you turn the bottle to the left or right.
Turn the bottle, and observe what happens. Record your observations.
4. Repeat Step 3, but this time, move the bottle forward at a steady speed.
5. Repeat Step 4, but this time, increase the speed.
Draw Conclusions
1. Compare the results of all these types of movement with one another. Were they
similar to or different from one another?
2. Inquiry Skill Scientists often form inferences to explain why something happened.
Infer why the bubble moved the way it did.
Investigate Further
Hypothesize what will happen to the air bubble if the bottle is moving at a steady
speed and its direction changes. Plan and conduct a simple investigation to test
your hypothesis.
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Reading in Science
VOCABULARY
position p. 144
speed p. 146
velocity p. 146
acceleration p. 148
SCIENCE CONCEPTS
 how different kinds of force affect motion
 how motion is measured
READING FOCUS SKILL
MAIN IDEA AND DETAILS Look for details that describe forces and motion.
Forces and Motion
Have you ever been sitting in an unmoving car when the car next to you started to
move? Did you feel as if you were moving forward or backward? When you looked
at the street you realized you weren't moving at all! In order to determine if an
object is moving, you must have a frame of reference. Your frame of reference is
the moving object and a background that isn't moving. If you were at the park
watching the girls on the swings, the trees and ground would help you determine
that the girls were changing their position.
You can tell the difference between a moving object and one that's still. But how would
you define motion? An object is in motion when its position changes. Position is
the location of an object in space, and it is always relative to a frame of reference.
We use many words to express position, such as east, west, above, below, and
beside.
Forces can make objects change their position. All forces—from gravitational force to
magnetic force to friction—are pushes and pulls. What force is making the girls on
the swings move?
---see picture
You know these girls are moving, because their positions are changing.
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Gravitational force is the force that attracts two objects. Gravitational force increases as
the objects' masses increase. Mass is the amount of matter in an object. If you get
out of a chair and walk around the room, your chair stays where it is, because Earth
is very large—the gravitational force it exerts i! strong.
Friction is a force that opposes motion. It either prevents motion or slows it down.
Friction acts between two surfaces. The smoother the surface is between two
objects, the less friction there usually is between them. This is why you slip on ice.
The smooth ice and the soles of your shoes don't produce much friction when they
slide past each other.
Often, several forces act together on an object. Think about an airplane in flight. Drag
from the air slows the plane. Thrust works against drag. Thrust is the forward force
produced by the plane's engine. Lift is the force that "pulls" the plane up, into the
sky. Gravity opposes lift. For the plane to fly, the forces of lift and thrust must be
equal to or greater than the opposing forces of gravity and drag.
MAIN IDEA AND DETAILS Why does a skydiver fall to the ground when she
jumps out of a plane?
---see pictures
Gravity pulls the girls down the slide. Friction slows their motion.
A maglev train doesn't have wheels. It uses magnetic force—the pull between
magnetic objects—to float above the track.
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Speed and Velocity
What makes a roller coaster so much fun? Many people think that it's the roller coaster's
speed. Speed is the distance an object travels in a certain amount of time. Speed
tells you how quickly or slowly something is moving.
An object's speed is an important property of its motion. Suppose you read that a certain
roller coaster zooms along 853 m (2800 ft) of track. Does that make you want to
ride it? Maybe. You read on and learn that the top speed of the roller coaster is 193
km/hr (120 mi/hr). It's the fastest roller coaster in the world. Now, that sounds like
fun!
You can calculate speed by using this formula.
speed = distance/time
If you walk 5 km (3.1 mi) in 1 hour, your speed is 5 km/hr. What is your speed if you
walk 10 km in 2 hours?
Sometimes you need to know the direction of an object as well as its speed. Suppose
some friends are meeting you at the park at 3:00. Will they be there on time? Yes—
if they're moving fast enough and in the right direction. In other words, your friends
must travel at the correct velocity. Velocity is the measure of an object's speed in a
particular direction.
Suppose your friends are walking southeast at a speed of 5 km/hr. Their velocity is 5
km/hr, southeast. Now suppose they pass another group of people walking 5 km/hr
in the opposite direction. The two groups are moving at the same speed but at
different velocities.
Math in Science Interpret Data
Vehicles and Record Speeds
The table shows world-record speeds for cars, planes, and boats. About how many
times as fast as the car is the plane? About how many times as fast as the boat
is the plane?
World's fastest car Thrust SSC, 1228 km/hr (763 mi/hr)
World's fastest plane X43-A, more than 10,800 km/hr (6800 mi/hr)
World's fastest boat Spirit of Australia, 511 km/hr (317.6 mi/hr)
The Thrust SSC is the world's fastest car. It set the world speed record for a car by
traveling at a speed of 1228 km/hr (763 mi/hr).
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A car traveling down a straight highway at a constant speed has constant velocity. This
means that the car is moving steadily in the same direction. It doesn't speed up or
slow down. It doesn't turn. It only moves in a straight line.
We can also describe velocity as changing. In this case, the object's speed is changing or
its direction is changing—or both. A car driving at a steady speed in a circle has a
changing velocity. The car's speed is constant, but its direction changes every
moment as it turns along the circle. When anything speeds up, slows down, stops,
starts, or turns, its velocity changes.
MAIN IDEA AND DETAILS What are four ways the friends walking to the park
can change their velocity?
Insta-Lab
What's the Speed?
Use a meterstick and tape to mark off a certain distance. Time the movement of several
objects (such as a marble, a wind-up toy, and a toy car) from start to finish. Then
calculate their speeds. Which moves the fastest?
Speed =110 km/hr (68.4 mi/hr)
Velocity = 110 km/hr (68.4 mi/hr), east
Velocity is a more complete way to describe an object’s motion. It includes the
object’s speed and its direction.
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Acceleration
A car's velocity changes slowly as it backs out of a parking spot. But its velocity
changes quickly if the driver slams on the brakes. Motion can be described by how
quickly an object changes velocity, or accelerates. Acceleration is the rate at which
velocity changes over time.
You can calculate acceleration by using this formula.
acceleration = change in velocity/time
Suppose you see an ad for a sports car that accelerates to 100 km/hr (62 mi/hr) in 5
seconds. What is its acceleration? Subtract the starting speed from the final speed
to find the change in speed. Divide the change in speed by the time it takes for the
speed to change. Use a for acceleration.
---see formula
The car is constantly accelerating by 20 km/hr during each second. At the end of one
second, the car's speed is 20 km/hr (12.4 mi/hr). After two seconds,
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the car is going faster. Now its speed is 40 km/hr (24.9 mi/hr). What is the car's speed
after three seconds?
The sports car also accelerates when it slows down or stops. Remember that
acceleration is the rate of change in the velocity. Velocity involves speed and
direction. So acceleration can happen through a change in either speed or
direction—or both.
Several parts of a car control its acceleration. The gas pedal causes the car o gain speed.
The brake slows down the car or stops it. The steering wheel changes he car's
direction.
An object has a large acceleration when it changes its velocity quickly. For example, a
motorcycle can have a lesser acceleration than a child's tricycle. Suppose the
motorcycle is zipping down a highway n a straight line at a constant speed. Its
acceleration is zero. But a tricycle in a driveway is accelerating as the rider slows
town, speeds up, or turns.
MAIN IDEA AND DETAILS What two properties of an object's motion can
change when it accelerates?
See pictures pgs 148 & 149
The whale thrusts the performer into the air with great force. As a result, the
performer's velocity changes—he accelerates.
A roller coaster car is almost always accelerating during a ride because its speed
and its direction are almost always changing.
A jet plane has limited runway space to land on the deck of an aircraft carrier.
The plane must come to a stop very quickly, so the acceleration of the plane is
large.
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Momentum
A truck and a car are cruising down a highway. They have the same speed, the same
velocity, and the same acceleration. Are the motions of the two vehicles the same?
The motion of the car differs from that of the truck in one important way—momentum.
Momentum is a property of motion that describes how hard it is to slow down or
stop an object. Momentum also describes how an object will affect something that
it bumps into. Momentum depends on mass and velocity. You can calculate
momentum by using this formula.
momentum = mass x velocity
In the example, the truck has a far greater mass than the car. So the momentum of the
truck is much greater than the momentum of the car. The truck will be harder to
stop or slow down. If the truck bumps into something, it will cause more damage
than the car.
However, objects with different masses can have the same momentum if the object with
less mass has more velocity. Momentum increases if either mass or velocity
increases.
Consider two football players. One is big and heavy, and the other is small and light.
Suppose the large player runs slowly and the smaller player runs quickly. They
could each have the same momentum. Each player could be equally hard to stop.
And each player could have an equally crushing effect on the other team!
MAIN IDEA AND DETAILS What two factors determine an object's momentum?
---see picture
A big truck moving at a fast speed has a lot of momentum. How much momentum
does this small car have?
1. MAIN IDEA AND DETAILS Copy and complete this graphic organizer.
2. SUMMARIZE Use your completed graphic organizer to write a lesson summary.
3. DRAW CONCLUSIONS A car is moving in a straight line at a constant speed of
40 km/hr. Is it accelerating?
4. VOCABULARY Use the vocabulary terms in this lesson to create a crossword
puzzle with answers.
Test Prep
5. Critical Thinking The speed of a ball falling from a high shelf to the floor is 9.8
m/s. What is its velocity?
6. A motorcycle is accelerating at a rate of 1 km/hr/s. If its speed is 20 km/hr after 5
seconds, what is its speed after 6 seconds?
A. 20 km/hr
B. 21 km/hr
C. 100 km/hr
D. 120 km/hr
Writing
Narrative Writing
Write a short story that features world records for fast movers. You might choose
animals, human runners, or vehicles. Use the vocabulary you have learned in this
chapter.
Math
Solve a Problem
Find the speed of a motorcycle that travels 32 km in 16 minutes. Show the formula you
used as well as your work.
Social Studies
Multicultural Studies
Compare the numbers of bicycles and cars in other countries with the numbers of these
vehicles in the United States. Write a report explaining your findings.
For more links and activities, go to www.hspscience.com
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