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Forces
First we need to define the word
FORCE:
•The cause of motion (what causes
objects to move)
•Two types of forces
- Pushes
- Pulls
Forces are measured in Newtons
• SI unit of force
• Symbol: N
• Measured by using a spring scale
Forces may be balanced or
unbalanced
• Balanced forces – all forces acting on
an object are equal
-There is NO MOTION
• Unbalanced forces – one or more
forces acting on an object are stronger
than others
-There is MOTION
A NET FORCE
Friction
Force that slows down motion.
There are three different types of
friction:
1. Rolling Friction
2. Sliding Friction
3. Fluid Friction
Rolling Friction
The friction that exists when a wheel turns
on a surface.
Sliding Friction
When two objects are rubbing against each
other.
Fluid Friction
The friction on a solid object as it moves
through water.
Gravity
• Force that attracts all objects toward each
other
• More mass = more gravity
• Acceleration because of gravity is 9.8 m/s/s
• All objects accelerate at the same rate
Newton’s Laws
• First Law – Inertia
• Second Law – Acceleration, Force &
Mass
• Third Law – Action-Reaction
First Law
• Inertia
– An object at rest [not
moving] remains at rest
unless acted on by a force
[push or pull]
– An object in motion
remains in motion unless
acted on by a force [push
or pull]
First Law
• Inertia & Mass
– Mass is the amount of matter in an object
– The more MASS an object has, the more INERTIA
the object has.
– Bigger objects are harder to start & stop
Second Law
• Acceleration & Force
– The more force placed on an object, the more it
will accelerate [change its motion]
• Acceleration & Mass
– The more mass [or inertia] an object has, the
more force it takes to accelerate the object
Third Law
• Action – Reaction
–Forces are always produced in pairs
with opposite directions & equal
strengths
–For every force there is an equal and
opposite force