Transcript newton`s_first_law_of_motion

Newton’s First Law of Motion
Summary of Newton’s 3 Laws:
• 1st Law – An object at rest will stay at rest,
and an object in motion will stay in motion at
constant velocity, unless acted upon by an
unbalanced force.
• 2nd Law – Force equals mass times
acceleration.
• 3rd Law – For every action there is an equal
and opposite reaction.
First we need to define the word
FORCE:
• The cause of motion (what causes objects
to move)
• Two types of forces
– Pushes
– Pulls
Slide from www.science-class.net
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
Balanced Force
Equal forces in opposite
directions produce no motion
Unbalanced Forces
Unequal opposing forces
produce an unbalanced force
causing motion
Demonstrating Force
• Slide a book across a
table and watch it slide
to a rest position.
• What force brings the
book to rest?
1st Law:
Objects at Rest or in Motion
• Objects at rest tend to
stay at rest unless acted
upon by a force. [push
or pull]
• Newton described this
tendency as inertia.
• Inertia can be
described as the
tendency of an object to
keep doing whatever’s
it’s doing.
Mass & Inertia
Which vehicle has more
inertia?
• 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
Slide from www.science-class.net
Newton’s 1st Law
(also known as the law of inertia)
• A moving object moves in a straight line with
constant speed unless a force acts on it.
• The tendency of an object at rest to remain
at rest and an object in motion to remain in
motion unless acted upon by an unbalanced
force.
• Objects do not change their motion unless
a force acts on them
Newton Saves Your Life
Newton’s 2nd Law
Checking for Understanding
1. What acceleration will result when a 12 N net force applied to a 3
kg object? A 6 kg object?
2. A net force of 16 N causes a mass to accelerate at a rate of 5
m/s2. Determine the mass.
3. How much force is needed to accelerate a 66 kg skier 1
m/sec/sec?
4. What is the force on a 1000 kg elevator that is falling freely at
9.8 m/sec/sec?
Demonstrating Newton’s 2nd Law
Newton’s 3rd Law
For every action there is an equal and
opposite reaction.