Transcript Forces and Motion - SharpSchool Redirect

Forces and Motion
4.05 Determine factors that affect motion including:
• Force
• Friction.
• Inertia.
• Momentum
Position and Direction
• The motion of any object can be described
by its position and how that position
changes over time. If an object moves
slowly, its position will also change slowly.
• Position is the location of an object.
• You can describe the motion of an object
by describing its original position and its
final position.
• Motion can also be described using the
directions north, south, east, and west.
• All motions can be described in terms of
position and direction.
• Position and direction are very helpful for
describing motion. However, motion also occurs
over time.
• Speed is a measurement of distance over time.
• Velocity measures distance over time but also
includes direction.
• For example, a soccer ball that moves 20 meters
in 2 seconds is moving with a speed of 10
meters per second. The velocity of that ball is 10
meters per second east.
Describing Motion
• Scientists use many tools to measure
motion. A compass will measure the
direction of a motion. A meterstick will
measure position. A stopwatch will
measure time. Scientists can then
calculate speed by dividing distance by
time.
• What is the speed of a baseball that
moves 40 meters in 5 seconds?
8 meters per second.
• Why is a compass a useful tool for
describing motion?
It describes direction.
Forces Change Motion
• A force is a push or pull on an object.
Forces cause objects to move or to stop
moving. There are many kinds of forces.
The motion of any object can be
understood by looking at all of the forces
that are acting on that object.
• Nothing can move without a force being
applied to it.
• The mass of an object tends to make the
object resist being set into motion. That’s
why objects with more mass are set into
less rapid motion by a certain amount of
force.
• The tendency of an object to resist a
change in its state of motion is called the
object’s inertia.
• Galileo, an Italian scientist, figured out
how inertia affects the motion of objects.
• He observed that pendulums swing back
and forth to the same height. He reasoned
that a ball rolling down one ramp and up
another would roll to the same height on
any ramp.
• Just as it takes a force to set an object in
motion, it also takes a force to slow or
stop a coasting object. Without any such
force, the object will coast forever in a
straight line.
• Friction opposes the motion of one object
moving past another. If the friction is taken
away, no force is needed to maintain
motion at a steady rate. An object’s inertia
is all that is needed to keep it moving.
• Forty-five years after Galileo died, Sir
Isaac Newton published a complete
description of the concept of inertia. This is
Newton’s first law of motion: Objects at
rest remain at rest and objects traveling at
a steady rate in a straight line continue
that way until a force acts on them.
• Newton’s first law of motion -- the law of
inertia -- tells us that the state of motion of
an object does not change until a force is
applied to it. That means, if an object is
traveling at a steady rate in a straight line,
it will continue to do so until a force is
applied to it. Newton’s law also means that
if the object is sitting at rest, it will continue
to be at rest until a force is applied to it.
• An object’s velocity changes if either its
speed or its direction changes.
• There are two forces that can affect an
object’s velocity:
1. Friction, a force that opposes the
motion of one object moving past
another.
2. Gravity, keeps the Earth moving in a
circular path about the sun.
• As long as an object travels in a straight
line at a steady speed, its velocity is
constant.
• Without the force of gravity, Earth would fly
off in a straight line into deep space.