Newtons First Law of Motion

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Newtons First Law of Motion
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Newtons First Law

• An object at rest remains at rest, and an object
  in motion continues in motion with constant
  velocity, unless acted upon by a net external
  force.

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Newtons First Law

• Inertia the tendency of an object to continue
  in its state of motion.
• Newtons First Law is also known as Newtons
  Law of Inertia.

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Newtons First Law

• Acceleration is determined by net external force.
• Net External Force the total force resulting
  from a combination of external forces on an
  object sometimes called the resultant force.

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Newtons First Law
Although there are several forces acting on this
car, the vector sum of the forces is zero, so the
car moves at a constant velocity.
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Newtons First Law

• Mass is a measurement of inertia.
• Objects in motion tend to stay in motion.

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Newtons First Law
Sample Problem 4A Derek Leaves his physics book
on top of a drafting table that is inclined at a
35? angle. The free-body diagram shows the
forces acting on the book. Find the net external
force acting on the book, and determine whether
the book will remain at rest in this position.
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Newtons First Law
Given Fgravity on book 22 N Ffriction 11
N Ftable on book 18 N Unknown Fnet ?
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Newtons First Law
Select a coordinate system, and apply it to the
free-body diagram. (If the book moves, it will
slide down the ramp.)
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Newtons First Law
Find the x and y coordinates of all
vectors. Ffriction is on the x-axis. Ftable on
book is on the y-axis. Fgravity on book is at
angle ? with the x-axis, therefore, ? 90-35
55?
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Newtons First Law
Find the x and y coordinates of all vectors.
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Newtons First Law
Find the sum of all x and y vectors.
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Newtons First Law
Find the net external force.
The net external force is acting along the
x-axis. The book slides down the ramp.
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Section 4 - 2Newtons First Law

• Assignment
• Practice 4A p 133 1-4
• Section Review p 135 1-5