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Use the Force!
Two forces combine to keep our planets
revolving around the sun; inertia and gravity.
Without these forces we would fly into space
traveling farther and farther from the sun! In
this investigation we will discover how these
forces combine to keep us at just the right
place in space.
Objective: Students will be able to define the forces of gravity and inertia
in order to describe how they combine to maintain the orbits of the planet.
Newton’s first law of motion states that an object in motion will stay in
motion in the same direction with the same speed unless acted on by another
force. This is known as the law of inertia. Inertia is the force resistant to
change. For example, if you have ever had to push a heavy object, it is
always hardest to get it moving. Once it’s moving the force of inertia helps
to keep the object moving making it easier to push. Keeping that in mind,
consider the following questions.
1. Raven’s quarterback, Joe Flacco, throws a pass to Todd Heap. However,
the object in motion, the football, does not stay in motion with the same
speed. Predict reasons why the football defies Newton’s first law of
motion and write them below.
2. If Flacco threw the pass to Todd Heap in space
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Everything that exists creates a force called gravity. Gravity is an attraction
force or pulling force. However, we are not sucked into the gravity of
lockers, students, or even buildings. Why do you think that is? The strength
of gravity is dependent on two things, distance from the object and mass
(weight) of the object. We can observe this on a scale. If we weighed an
infant on a scale and a full grown adult we would expect that the adult would
weigh more. That is because the more mass they have the stronger they are
attracted to Earth. Similarly, all objects in space are pulled into our sun
because they are too far away to be affected by our gravity.
Observe the pictures and circle the object that would have the greatest
amount of gravity.
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2. Circle the “X” that would be most affected by the flag’s gravity.
X
X
X
X
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Our elliptical orbits are caused by a combination of
forces, inertia and gravity. The sun’s gravity pulls the
planets inward and the inertia of the moving planets
pulls the planets in a perpendicular direction (see
image). Neither force is great enough to overcome
the other. Therefore, the planets are locked in orbit
around our sun.
Analysis
1. When researching our planets we noticed that the inner planets were
primarily made of heavy rocks and metals while the outer planets were made
of gasses. Using evidence from the investigation, explain why this may
have happened.
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