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An Introduction to Forces:
More Practice
Draw a free-body diagram
for each of the following
objects:
(a) A car engine being lifted
from a car by a rope
attached to a pulley
An Introduction to Forces:
More Practice
Draw a free-body diagram
for each of the following
objects:
(b) an car moving with
constant velocity on a
level road
An Introduction to Forces:
More Practice
Draw a free-body diagram
for each of the following
objects:
(c) an apple hanging from a
tree branch
An Introduction to Forces:
More Practice
Draw a free-body diagram
for each of the following
objects:
(d) a skydiver being slowed
by a parachute
An Introduction to Forces:
More Practice
Ms. Rosebery is pulling across level snow a sled on
which is sitting her daughter Ivy. Tied to the
back of Ivy's sled is another tiny sled on which
Ivy's baby doll is sitting.
Draw the free-body diagrams for (a) Ms. Rosebery
An Introduction to Forces:
More Practice
Ms. Rosebery is pulling across level snow a sled on
which is sitting her daughter Ivy. Tied to the
back of Ivy's sled is another tiny sled on which
Ivy's baby doll is sitting.
Draw the free-body diagrams for (b) Ivy
An Introduction to Forces:
More Practice
Ms. Rosebery is pulling across level snow a sled on
which is sitting her daughter Ivy. Tied to the
back of Ivy's sled is another tiny sled on which
Ivy's baby doll is sitting.
Draw the free-body diagrams for (d) Ivy’s sled
An Introduction to Forces:
More Practice
Ms. Rosebery is pulling across level snow a sled on
which is sitting her daughter Ivy. Tied to the
back of Ivy's sled is another tiny sled on which
Ivy's baby doll is sitting.
Draw the free-body diagrams for
(d) Ivy’s doll’s sled
Newton’s 1st Law of Motion:
Learning Goal
The student will be able to state Newton’s 1st Law
and apply it in qualitative and quantitative terms
to explain the effect of forces acting on objects.
(B3.4)
st
1
Newton’s Law of
Motion
Net Force
The net force is the sum of all forces acting on an
object.
Example: A weightlifter holds a weight above his
head by exerting a force of 1.6 kN [up]. The
force of gravity acting on the weight is 1.6 kN
[down]. Draw a FBD of the weight. What is
the net force on the weight?
Net Force
FA=1.6 kN
Fg=1.6 kN
Net Force
FA=1.6 kN
Fg=1.6 kN
The net force is zero: 1.6 kN + (-1.6 kN) = 0
Newton’s First Law of Motion
If there is no net force acting on an object, the
object will remain at rest
Newton’s First Law of Motion
If there is no net force acting on an object, the
object will remain at rest
Newton’s First Law of Motion
If there is no net force acting on an object, the
object will remain at rest or will keep moving at
the same constant velocity.
Newton’s First Law of Motion
If there is no net force acting on an object, the
object will remain at rest or will keep moving at
the same constant velocity.
(Conversely, if an object is at rest or is moving at
constant velocity, there is no net force acting
upon it.)
Inertia
This is the principle of inertia, first articulated by
Galileo:
Inertia
“Inertia is a property
of matter.”
Inertia is the property of matter that causes it to
resist changes to its motion.
The greater the mass of an object, the greater its
inertia.
Newton’s First Law of Motion
Question: An object is being pushed along at
constant velocity by a force of 5 N [left]. What
is the force of friction acting on the object?
Newton’s First Law of Motion
Question: An object is being pushed along at
constant velocity by a force of 5 N [left]. What
is the force of friction acting on the object?
If the velocity is constant, there is no net force, so
the force of friction must be equal in magnitude
and opposite in direction to the applied force:
Newton’s First Law of Motion
Question: An object is being pushed along at
constant velocity by a force of 5 N [left]. What
is the force of friction acting on the object?
If the velocity is constant, there is no net force, so
the force of friction must be equal in magnitude
and opposite in direction to the applied force:
Ff = 5 N [right]
More Practice
Explaining Why with Newton’s 1st Law of Motion