Transcript Newton`s Laws of Motion

Newton’s Laws of Motion
Miss Barnes
Sir Isaac Newton
 http://www.biography.com/articles/SirIsaac-Newton-194903
st
1 Law of Motion
 An object in motion will stay in
motion unless a force acts on it.
 An object at rest will stay at
rest unless a force acts on
it.
Define it!
 Science journals out!
 Write the word:
Inertia
 Write the definition:
The tendency of an object to resist any change
in motion.
st
1 Law of Motion
Objects with more mass will have more
inertia than objects with less mass.
Have you ever been forced against the
side of a car as it turns?
When the car is changing direction, your body
tends to keep moving straight.
The car is pushing on you during a turn.
st
1 Law of Motion
Think of a crash test
The car crashes and stops.
The dummy has inertia and wants to keep
going forward.
The seatbelt is what keeps the dummy from
continuing to move forward.
WEAR YOUR SEATBELT!!!
Keyword:
AccelerationThe rate at which the speed of an
object changes over time.
nd
2 Law of Motion
Mass, acceleration, and force are related.
The law indicates the stronger the force acting
on an object, the more the object will
accelerate.
A force will cause an object with small mass to
accelerate more than an object with a large
mass. (same force)
Acceleration due to a small force on a small
object can be the same as the acceleration of a
big force on a big object.
2nd Law of Motion
The greater the force pushing on the box,
the greater the acceleration of the box
The greater the mass of the box, the less
the acceleration will be.
3rd Law of Motion
When one object exerts a force on a second
object, the second object exerts a force on
the first object.
For every action there is an equal and
opposite reaction.
3rd Law of Motion
When a person leans on a wall they exert
force on the wall.
 The wall exerts an equal force on the person in
the opposite direction.
When two bumper cars collide, both drivers
feel the impact.
Each car gave off an equal and opposite force.
Balanced Force
Balanced forces do not cause a change in
motion. They are equal in size and opposite
in direction.
Push both of your hand together with the same
force.
The force is equal in size and opposite in direction,
therefore there is no motion.
Balanced Forces
In a balanced force the two forces cancel
each other out and therefore there is no
motion.
Think about arm wrestling or tug-o-war.
Unbalanced Forces
 Unbalanced forces always cause a
change in motion. They are not equal
and opposite.
Unbalanced Forces
Think again about the arm
wrestling match. Only this
time imagine that you are
competing against a
world famous body
builder. Chances are that
his force will be much
greater than yours. Your
arms will move in the
direction he is pushing
with a force that is equal
to his force minus your
force. It will look like this.
Unbalanced Forces
Unbalanced forces can also be exerted in the same
direction. For example, imagine that your family's car
breaks down on the road and you have to push it into a
parking lot. If you and your brother or sister both push on
the car, the resulting force on the car will be the sum of
your forces and of course be in the direction that you are
applying the force. The figure below shows how this would
work.