8.1 - An object’s
inertia causes it to continue moving the way it is moving unless it is acted
upon by an (unbalanced) force to change
its motion. An unbalanced force is a net force.
"Every
object remains in a state of rest or of uniform motion in a straight line
unless acted upon by an outside force." (An outside force is a net force.)
Inertia is the resistance to changes in motion.
Inertia is proportional to mass. Big masses resist changing their motion more
than smaller masses.
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Objects at rest remain at rest unless acted on by a net force. |
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A lot of inertia! The large train resists changing its motion. |
Very little inertia. The small baby carriage has very little resistance to changes in motion. |
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Since the train is so huge, it is difficult to change its speed. In fact, a large net force is required to change its speed or direction. |
Since the baby carriage is so small, it is very easy to change its speed or direction. A small net force is required to change its speed or direction. |
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Objects in motion remain in motion in a straight line (unless acted upon by an outside force). |
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A lot of inertia! |
Very little inertia |
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Since the train is so huge, it is difficult to stop it once it is moving. It is difficult to change its speed. In fact, a large net force is required to change its speed. |
Since the soccer ball is so small, it is very easy to stop it once it is moving. A small net force is required to change its speed. |
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What is the difference between inertia and momentum? |
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Inertia is proportional to mass. It is a measure of the resistance to changes in velocity. |
Momentum = mass x velocity |
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Inertia is a property of mass and cannot change. Momentum changes as an object changes its velocity. |
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Some
other types of inertia:
Gyroscopic Inertia = "A body that is set spinning
has a tendency to keep spinning in its original orientation."
For example, a top or gyroscope will not fall over when it is
spinning.
Rotational Inertia = the property of an object
that resists any change in its state of rotation. If at rest, it tends to
remain at rest; if rotating, it tends to remain rotating and will continue to
do so unless interrupted. For example, think of a metal ring and a solid
disk experiment. The metal ring has its mass at the perimeter and therefore has
more rotational inertia than the solid disk. This is why a ring resists rolling
from a state of rest.