Transcript 4.1 The cause of forces

Motion and Force
Chapter Four: Forces
• 4.1 Forces
• 4.2 Friction
• 4.3 Forces and Equilibrium
Investigation 4A
What is a Newton?
• What is force and
how is it measured?
4.1 The cause of forces
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A force is a push or pull, or any action
that has the ability to change motion.
The key word here is action, force is an
action.
4.1 The cause of forces
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Fundamentally, forces come from the
interaction between atoms and energy.
4.1 Units of force
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When you measure weight in pounds on
a scale, you are measuring the force of
gravity acting on the object.
The word “pound” comes from the Latin
word pondus, which means “weight.”
4.1 Units of force
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The newton (N) is
a metric unit of
force.
A force of 1 newton
is the exact amount
of force needed to
cause a mass of 1
kilogram to speed
up by 1 m/s each
second.
4.1 Converting newtons and
pounds
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One pound of force equals 4.48 newtons.
4.1 Gravity and weight
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The force of gravity on an object is called
weight.
Mass and weight are not the same thing!
4.1 Gravity and weight
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A 10-kilogram rock has a
mass of 10 kilograms no
matter where it is in the
universe.
A 10-kilogram rock’s
weight however, can
vary greatly depending
on where it is.
4.1 Calculating weight
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The weight equation can be rearranged
into three forms to calculate weight, mass,
or the strength of gravity.
4.1 The force vector
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A force vector has
units of newtons, just
like all forces, but
also includes enough
information to tell the
direction of the force.
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Positive and negative numbers indicate
opposite directions.
4.1 Addition of vectors
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It is sometimes helpful to show the strength
and direction of a force vector as an arrow.
When drawing a force vector, you must choose
a scale.
If 1 cm = 1 N, how many newtons
of force does this line represent?
4.1 Forces in springs and ropes
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Tension is a force that acts in a rope,
string, or other object that is pulled.
Tension always acts along the direction
of the rope.
In what
direction will
each boy go?
4.1 Forces in springs and ropes
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When you apply a
compression force to
a spring, it collapses
to become shorter.
The force created by
stretching or
compressing a spring
always acts to return
the spring to its
natural length.