Download Balanced Forces

Newton’s Laws
of Motion
Sir Isaac Newton says:
“In order to move an object with mass,
you need to apply a force”
The greater the mass = The greater inertia => more force is needed
Force
• Force – A push or pull that
causes an object to accelerate
1000 kg
Balanced vs. Unbalanced
Forces
• Balanced Forces - no acceleration in
any direction
• Unbalanced Forces – one force is
greater than the other causing
acceleration in a direction
Balanced Forces
5N
Object
5N
Equal Pushing
Forces will cancel each other and
produce NO ACCELERATION!
Balanced Forces
If these football players push
on each other equally as hard,
will either one move?
Balanced Forces
Ground pushes up
Gravity pulls down
Gravity pulls down on you, the ground pushes
back up, KEEPING YOU WHERE YOU ARE!
Unbalanced Forces
10 N
Object
5N
Not Equal Pushing
Forces will not cancel each other out and
produce ACCELERATION!
Unbalanced Forces
Forces will not cancel each other out and
produce ACCELERATION!
Balanced vs. Unbalanced
Forces
Video
First Law of Motion
• Inertia – An object’s resistance to a
change in its motion.
• Newton’s 1st Law of Motion:
– an object at constant speed stays at constant speed unless
acted upon by an outside force
– An object at rest stays at rest unless acted upon by an outside
force
The 1st Law is known as the Law of Inertia.
Newton’s First Law and You
Because of inertia, objects (including you)
resist changes in their motion. When the car
going 80 km/hour is stopped by the brick
wall, your body keeps moving at 80 m/hour.
Second Law of Motion
• The acceleration of an object is proportional
to the Force acting on the object, but
inversely proportional to the object’s mass.
• Force = mass  acceleration (F = m  a)
• More Force = More Acceleration
• More Mass = Less Acceleration
Second Law of Motion
• If you apply
more force to
an object, it
accelerates at
a higher rate
Second Law of Motion
• If the same
force is applied
to an object with
greater mass,
the object
accelerates at a
slower rate
because mass
adds inertia
Second Law of Motion
Second Law of Motion
• A car rolls down a ramp with a force of 2
newtons. The car has a mass of 0.5 kg.
What is the acceleration of the car?
• F=ma
• (2 N)  (0.5 kg) = 4 m/s2
Third Law of Motion
• When one object exerts a force on a second
object, the second exerts an opposing force
with equal value and in the opposite
direction on the first.
Upward
motion
Downward
force
Third Law of Motion
• Third law forces are often called
Action-Reaction Pairs.
F12 = – F21
These forces do NOT
act on the same object!
Third Law of Motion
Third Law of Motion