Download Force

Force
A push
or pull
exerted
on an
object.
Forces…

Forces are vectors
– Have both magnitude and directions

Net Force
– Vector sum of all forces acting on a body

When the net force on an object is zero,
the object is in equilibrium
– In otherwords, the acceleration is zero.
Force & Motion

Forces cause accelerations
– Change in velocity
 Speed and/or direction
Consider the book
on the table. In
order for the book
to move, an
unbalanced force
has to act on the
book.
Systems
When considering how a force
affects motion, it is important to
identify the object of interest.
This object is called the system.
Everything around the object
that exerts forces on it is called
the external world.
The identifiable cause is called
an agent.
Contact Forces
•
A contact force exists when an object from
the external world touches a system and
thereby exerts a force on it.
Friction
Tension
Normal
Applied
Field Forces

Field forces are exerted without contact.
– Also known as non contact forces or action at
distances forces
Gravitational
Electrical
Magnetic
Free Body Diagram
Free Body Diagram: a physical model that
shows all the forces acting on the system.
Each force is drawn as a vector
leading away from the object.
*Must be drawn for every problem
FBD Example

A car accelerating to the right
experiencing friction.
Normal
Applied
Friction
Weight
Newton’s First Law

An object in motion, stays in motion; an
object at rest stays at rest unless acted on
by a net force.
Also known as the law of inertia!!!
Inertia…
Inertia
An object’s resistance to change its state
of motion.
 An object’s mass is a measurement of the
object’s inertia.

– The more mass an object has, the more
resistance it will have to change its state of
motion.
Mass vs. Weight

Mass
–
–
–
–

Amount of matter present in an object
Constant – same everywhere in the universe
A measurement of an object’s inertia
Measured using a BALANCE
Weight
–
–
–
–
Force due to gravity
W = mg
Changes as the acceleration due to gravity changes
Measured using a SCALE
Newton’s

nd
2
Law
Acceleration is directly proportional to the
net force acting on the object and
inversely proportional to the object’s mass.

F = force
– Measured in Newtons

m = mass
– Measured in kilograms

a = acceleration
– Measured in m/s2
Newton’s

rd
3
Law
For every action force there is an equal
and opposite reaction force.
Interactions
All forces result from interactions between
objects.
 Action-Reaction force pairs act on different
objects.

– Action-Reaction forces do NOT cancel out
because they act on different objects.