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Physics Section 4.1
Define and apply forces
A force is a physical
quantity that can affect an
objects state of rest or
motion.
Forces can cause objects to:
a. Start moving
b. Stop moving
c. Change velocity/direction
The SI unit of force is the
Newton (N)
One Newton is the force
that will cause a mass of
one kilogram to accelerate
at a rate of one m/s2.
N = kg∙ m/s2
Weight is expressed in Newtons,
because weight is the force
exerted on an object due to
gravity. A one kilogram mass
weighs 9.8 Newtons.
Types of Forces
1. Contact forces- result
from physical contact.
(push, pull, etc…)
Draw a force diagram to
represent the forces acting
on a block with a weight of
5.0 N while it is being pulled
forward with a force of 4.0 N
on a frictionless surface.
2. Field forces- does not
involve physical contact.
(gravity, magnetism,
electrical, etc…)
Forces have both magnitude and direction. They are
vector quantities.
• Assignment:
• Page 124
• Problems 1 - 5