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
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A push or pull on an object.
Described by:
•STRENGTH
•DIRECTION
A force gives an object energy to:
•STOP MOVING
•START MOVING
•CHANGE DIRECTION

Contact Force

Non Contact Force

Contact
How do these relate to
the title of this lesson?
(Gravity and Friction?)

Noncontact
Contact = friction
Noncontact = gravity


A push or pull on one object by another that
is touching it.
Contact forces can be:
 Strong
OR
 Weak


A force that one object can apply to another
object without touching it.
Examples Include:



Gravity
Magnetic Force
Electric Force




ARROWS can be used to show forces.
LENGTH
The
of an arrow shows the
STRENGTH of the force.
The DIRECTION
that the arrow points
shows the direction in which the FORCE WAS
APPLIED
The stronger the force the LONGER the
arrow.

The SI unit for force is the NEWTON

The symbol for Newton is N


One Newton = about the force you exert to
lift a lime.
Named after: Sir Isaac Newton (founder of
physics)



An attractive force that exists between all
objects that have mass.
On EARTH the force of gravity = 9.8 m/s2
All objects fall to the Earth at an acceleration
of 9.8m/s2 due to the force of gravity.

Sir Isaac Newton (1600’s)

The law states:

Factors Affecting Gravity
All objects are attracted to each
other by a gravitational force. The
strength of force depends on the
MASS of each object and the
DISTANCE between them.
•MASS
•DISTANCE

The amount of matter in an object.



When the mass of one or both objects INCREASES
the gravitational force between them also INCREASES
Regardless of the amount of mass an object has
the FORCE ARROWS will be the SAME SIZE
Each object exerts the
other object.
SAME
attraction on the
The attraction between objects DECREASES
as the DISTANCE between the object INCREASES


The gravitational force exerted on an object.

Weight is measured in NEWTONS

Near Earth’s surface the object’s weight is the
FORCE DUE TO GRAVITY

Weight and mass are related, but ARE NOT the
same.

Weight can
CHANGE due to GRAVITY

Mass DOES NOT change
FORCE = MASS x ACCELERATION
F= MxA
Weight on Earth = MASS x 9.8m/s2 (acceleration
due to the force of gravity)


What would an object with a mass of 10 kg
weigh?
If your mass was 50kg, what would your
weight be?


The combination of all the forces acting on an
object.
To calculate the net force:
◦ If the forces act in the same direction they are
added together.
◦ If forces act in opposite directions they are
subtracted.



Forces acting on an object that combine and
form a net force that is not zero.
Unbalanced forces cause an object to move.
Forces moving in the same direction are
ADDED

Forces moving in the opposite direction are
SUBTRACTED

Forces acting on an object that combine and
form a net force of ZERO. NO change in
motion.


A force that resists the motion of two
surfaces that are touching.
Types of friction
•STATIC FRICTION
•SLIDING FRICTION
•FLUID FRICTION
Friction that acts
on objects that
are not moving.

When solid objects
slide over each other.

A force produced by a fluid (gases or liquids)
Examples: engine oil, grease


Air resistance
•a type of fluid friction
•Upward force exerted on falling objects.

Air resistance is affected by: •SHAPE
•SIZE
•MASS
*objects with more surface area have more air resistance**
2 causes of friction
 When microscopic dips and bumps that cover
surfaces slide past another surface with dips and
bumps they catch on to one another.
 When a positive charge slides by a negative
charge attraction occurs.