Download 1.Type of Forces

Introduction to Forces
Force is a push or pull. It is a vector quantity measured
in Newtons (N) where one Newton is the amount of
force required to give a 1-kg mass an acceleration of 1
m/s/s. Thus:
1 Newton = 1 kg • m/s2
1.Type of Forces
Contact Forces
Action-at-a-Distance Forces
Frictional Force
Gravitational Force
Tension Force
Electrical Force
Normal Force
Magnetic Force
Air Resistance Force
Applied Force
Spring Force
Type of Force
(and Symbol)
Description of Force
Applied Force An applied force is a force that is applied to an object by a person
Fapp or Fa
or another object.
 e.g. If a person is pushing a desk across the room, then
there is an applied force acting upon the object.
The force of gravity is the force with which the earth or other
Gravity Force massively large object attracts another object towards itself.
Fgrav or Fg
On Earth all objects experience a downward force of gravity. The
(also known as force of gravity on earth is always equal to the weight of the
Weight, W) object, w:
Fgrav = m * g
where g = 9.8 N/kg (on Earth) and m = mass (in kg)
Do not confuse weight with mass. Mass (kg) is the amount of
matter that an object is made of. Weight (N) is the force of
gravitational attraction. Mass is constant throughout the universe
but weight changes depending on where you are.
Normal Force The normal force is the support force exerted upon an object
Fnorm or FN
that is in contact with another stable object.
 e.g. If a book is sitting on a table, then the table is
exerting an upward force upon the book in order to support
the weight of the book. This upwards support is the normal
force.
On a level surface, the normal force is equal in magnitude but
opposite in direction to the force of gravity. FN = - Fgrav
The normal force is perpendicular to the surface.
 e.g. If a person leans against a wall, the wall pushes
horizontally on the person.
Friction Force The friction force is the force exerted by a surface as an object
Ffrict or Ff
moves across it (sliding friction) or makes an effort to move
across it (static friction).
Friction depends upon the nature of the surfaces involved and
upon the degree to which they are pressed together. The
maximum amount of friction force that a surface can exert upon
an object can be calculated using the formula below:
Ffrict = µ • Fnorm
where µ = coefficient of friction (tables available)
Air Resistance Air resistance is a special type of frictional force that acts upon
Force
objects as they travel through the air. The force of air resistance
Fair or R
is often opposite to the motion of an object.
It is often negligible but is discussed for objects that travel at
high speeds (e.g., a skydiver or a downhill skier) or for objects
with large surface areas (e.g. hot air balloon).
Tension Force The tension force is the force that is transmitted through a
Ftens or T
string, rope, cable or wire when it is pulled tight by forces acting
from opposite ends. The tension force is directed along the length
of the wire and pulls equally on the objects on the opposite ends
of the wire.
Spring Force
Fspring or Fs
The spring force is the force exerted by a compressed or
stretched spring upon any object that is attached to it.
adapted from physics classroom
2. Drawing Free-Body Diagrams (Draw one for EVERY force question!)
1. Represent the object as a box
2. Represent all forces as arrows
 The arrows are vectors so their direction is critical
 Start in the centre and draw outwards
 The size of the arrow represents the magnitude of the force
1. A textbook sits motionless on a desk.
2. A car accelerates forwards from rest.
3. A block of wood slides down an incline.
Introduction to Forces
Force is a ______ or ______. It is a ___________
quantity measured in Newtons (N) where one Newton is the
amount of force required to give a 1-kg mass an acceleration
of 1 m/s/s. Thus:
1 Newton = 1 kg • m/s2
1.Type of Forces
Contact Forces
Action-at-a-Distance Forces
Frictional Force
Gravitational Force
Tension Force
Electrical Force
Normal Force
Magnetic Force
Air Resistance Force
Applied Force
Spring Force
Type of Force
(and Symbol)
Description of Force
Applied Force An applied force is a force that is ___________ to an object by
Fapp or Fa
a person or another object.
 e.g. If a person is pushing a desk across the room, then
there is an applied force acting upon the object.
The force of gravity is the force with which the earth or other
Gravity Force massively large object ___________ another object towards
Fgrav or Fg
itself.
(also known as On Earth all objects experience a downward force of gravity. The
Weight, W) force of gravity on earth is always equal to the weight of the
object, w:
Fgrav = m * g
where g = 9.8 N/kg (on Earth) and m = mass (in kg)
Do not confuse weight with mass. Mass (kg) is the ___________
_________ that an object is made of. Weight (N) is the
___________of gravitational attraction. Mass is
___________ throughout the universe but ___________
changes depending on where you are.
Normal Force The normal force is the ___________ ___________exerted
Fnorm or FN
upon an object that is in contact with another stable object.
 e.g. If a book is sitting on a table, then the table is
exerting an upward force upon the book in order to support
the weight of the book. This upwards support is the normal
force.
On a level surface, the normal force is equal in magnitude but
opposite in direction to the force of gravity. FN = - Fgrav
The normal force is ___________ to the surface.
 e.g. If a person leans against a wall, the wall pushes
horizontally on the person.
Friction Force The friction force is the force exerted by a ___________ as an
Ffrict or Ff
object moves across it (___________ friction) or makes an
effort to move across it (___________friction).
Friction depends upon the nature of the surfaces involved and
upon the degree to which they are pressed together. The
maximum amount of friction force that a surface can exert upon
an object can be calculated using the formula below:
Ffrict = µ • Fnorm
where µ = coefficient of friction (tables available)
Air Resistance Air resistance is a special type of ___________ force that acts
Force
upon objects as they travel through the air. The force of air
Fair or R
resistance is often opposite to the motion of an object.
It is often ___________ but is discussed for objects that travel
at high speeds (e.g., a skydiver or a downhill skier) or for objects
with large surface areas (e.g. hot air balloon).
Tension Force The tension force is the force that is transmitted through a when
Ftens or T
___________, ___________, ___________, or ___________
when it is pulled tight by forces acting from opposite ends. The
tension force is directed along the length of the wire and pulls
equally on the objects on the opposite ends of the wire.
Spring Force
Fspring or Fs
The spring force is the force exerted by a compressed or
stretched ___________ upon any object that is attached to it.
adapted from physics classroom
2. Drawing Free-Body Diagrams (Draw one for ___________ force question!)
1. Represent the object as a box
2. Represent all forces as arrows
 The arrows are vectors so their direction is critical
 Start in the centre and draw outwards
 The size of the arrow represents the ___________ of the force
1. A textbook sits motionless on a desk.
2. A car accelerates forwards from rest.
3. A block of wood slides down an incline.