Download Forces File


Force: A push or a pull
 Describes why objects move
 Defined by Sir Isaac Newton
Newton’s Laws

Newton’s First Law:
 An object at motion stays in motion unless
acted upon by a net force
 In other words: no net force means no
change in motion.

Newton’s 2nd Law:
F = ma
 Measured in Newton’s
○ 1 N = 1 kg * m/s2

Newton’s 3rd Law:
 When an object exerts a force on a second
object, the second exerts a force equal in
magnitude but opposite in direction to the
first.
○ Action-reaction forces
Types of Forces

Gravity: considered to be straight
downward.
 Symbolized Fg or W
 Also called Weight
 Fg =

Normal Force: force perpendicular to
the surface of contact between two
surfaces.
 The force of contact between 2 surfaces.
Net Force

Net force is the sum of all forces acting on
an object in a particular direction.

Fnet = mass of object * actual acceleration
of the object in that direction

No acceleration means net force = 0 N
 Constant velocity, object at rest
 Equilibrium
Free-Body Diagrams

Simple sketches that show all forces
acting on an object.

You and a friend push a large box
across the floor. You push with a force
of 100 N, your friend pushes with a force
of 85 N. The force of friction on the box
is 40 N. The box has a mass of 60 kg.
Draw a free body diagram showing all
forces acting on the box. Determine the
net force acting on the box. What will be
the acceleration of the box? How far will
the box have moved after 3 seconds?
Finding net force/acceleration

A 14 kg box is being pulled up a ramp
inclined at 27 degrees above the
horizontal with a force of 140N. The
force of friction acting on the box is 35
N. What will be the acceleration of the
box?
Homework
Pg. 124 #1-2 Practice A
 Pg. 128 #1-3 Practice B
 Pg. 129 #1-5 Section Review


Friction: the force that opposes motion
between 2 surfaces.