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Motion And Forces
SC-05-1.2.1 & SC-06-1.2.1
May the force be with you!
Mass vs. Weight

Mass is the amount of “stuff” in an object, or the
measure of inertia of an object.

Weight is the pull of gravity on an object.
– An object’s mass is the same throughout the
Universe, but your weight changes depending on
what planet your on.
– Because the gravitational pull on Mars is less than
Earth, you weigh less on Mars, but your mass is the
same at both locations.
Motion
Motion
is the change in
position of an object,
measured by distance and
time.
Force
A
force is any push or pull on an
object.
– Forces give energy to objects.
– Forces cause a change in the motion of
an object.
Frame of reference

The point from which movement is
determined.
– To measure movement, some point must be
considered as nonmoving.
– Earth is the most common frame of reference.
Speed

The distance traveled by a moving object
per unit of time.
– To calculate speed, use the equation:
Speed = distance/time
- Speed only gives distance and time.
Average Speed
The speed of a moving object is not
always constant
 Average speed = total distance/total time

Velocity

Velocity is the speed of an object in a
given direction.
– Velocity gives distance, time and the direction
of travel.
Acceleration

Is the change of speed over time.

Deceleration occurs when the change in
speed, or acceleration, is in the negative
direction.
– Commonly used to mean a decrease in speed.
Sir Isaac Newton

An English mathematician and physicist
who discovered one of the most important
relationships in physics: the relationship
between the force on an object, its mass,
and its acceleration.
Newton’s First Law of Motion

An object will stay at rest, while an object
in motion will stay in motion, unless acted
upon by an unbalanced force.
* In other words, unless you apply a force
to an object, it tends to keep doing what it
was doing in the first place.
Inertia

Newton was the first to use the term
inertia to describe the tendency of object
to remain in motion or stay at rest. Inertia
comes from the Latin word iners, which
means lazy.
Newton’s Second Law of Motion

The acceleration of an object is directly
related to the force acting on it and
inversely related to the object’s mass.
 Force = mass x acceleration
– In other words, force causes an object to
accelerate, while the object’s mass resists
acceleration.
Newton’s Third Law of Motion

For every action, there is an equal but
opposite reaction.

In other words, all forces act in pairs
Friction

Friction is a force that opposes motion.
– Friction always works against the motion that
produces them.
– There are 3 types of friction:
 Fluid Friction
 Sliding Friction
 Rolling Friction