Mechanical Equilibrium
Force – a push or a pull
Equilibrium – equality on 2 sides of something
Thermal Equilibrium – a thermometer acquires
the same temperature as what it is measuring
Mechanical Equilibrium – the object is stable,
there are no changes in its motion
A force is needed to change an objects motion
Net Force
Most often, more than 1 force acts on an object
at the same time.
Net Force is the combination of all forces acting
on an object.
Tension – stretching force (springs, rubber
bands, etc.)
Weight – force of gravity pulling on the mass of
an object
Vector – an arrow that represents the
magnitude and direction of a quantity
Vector Quantity – needs both magnitude and
direction for a complete description
Force is a vector quantity
Scalar Quantity – can be described by
magnitude only, has no direction
Time, area and volume are scalar quantities
Exercises Worksheet:
2.1 Force
Mechanical Equilibrium – no physical changes
occur; it is a state of steadiness
Equilibrium Rule – When a net force is 0, the
object is in mechanical equilibrium
ΣF=0
(the sum of all of the forces is equal to zero)
Support Force
Support force is the upward force that acts
opposite the force of gravity.
Support force is often called normal force.
For an object to be at rest, the magnitude of
the support force has to be equal to the
magnitude of the object’s weight. The direction
of the 2 forces will be opposite.
Bathroom Scale
The mechanism of the
scale is calibrated to
measure the support force
in the compressed spring.
This support force is equal
to the person’s weight.
The state of rest (not moving ) is only one form
of equilibrium.
Equilibrium is the absence of a change in
motion – so, an object moving at a constant
speed and not changing direction is also in
equilibrium.
A hockey puck sliding in a straight line at a
constant speed along the ice is in equilibrium.
Static Equilibrium – objects that are at rest.
Dynamic Equilibrium – objects moving at a
constant speed and in a consistent direction.
Bad Physics Pick-up Line:
I was only scalar until you came along and gave
me direction.
The person suspended by the
rope has a weight of 300 N.
The tension on the scale,
therefore, reads 300 N.
If the person is hanging by one
rope, then it is going to have
tension equal to the person’s
weight.
But, if the person is hanging by
2 ropes, the tension is divided
between the 2 ropes, and so
on.
Combining Vectors
For Parallel Vectors:
If they are in the same direction, they add.
If they are in opposite directions, they subtract.
The sum of two or more vectors is called their
resultant.
Combining Vectors
For Non-Parallel Vectors:
Parallelogram Rule – construct a parallelogram
so that the 2 vectors are adjacent sides.
The vectors are
perpendicular.
The two vectors make
adjacent sides.
The resultant is the vector
at the center of the point
where the two vectors
meet.
Non-parallel and non
perpendicular vectors
Assignment