What is a Force? A force can cause a resting object to move, or
it can accelerate a moving object by changing the objects speed or
direction. Spring scale is used to measure force Force is measured
in Newton (N) 1N = 1Kg 1m/s 2
Slide 3
Representing force Can use an arrow to represent the direction
and strength of a force. The direction of the arrow represents the
direction of the force. The length of the arrow represents the
strength or magnitude of the force.
Slide 4
Representing Force Calculating Net Force from arrows If arrows
are in same direction they add together If arrows are in opposite
directions they subtract from each other A.4 N force down B.0 N
force C.4 N force left D.6 N force up
Slide 5
Friction Friction is a force that opposes the motion of objects
that touch as they move past each other. Friction acts at the
surface where object are in contact Four main types of friction:
static friction, sliding friction, rolling friction and fluid
friction.
Slide 6
Static Friction Static friction is the friction force that acts
on objects that are not moving. Static friction always acts in the
direction opposite to that of the applied force Prevents objects
from sliding.
Slide 7
Sliding Friction Occurs when there is enough force to overcome
the static friction Sliding Friction is a force that opposes the
direction of motion of an object as it slides over a surface. There
will be a net force in the direction of motion
Slide 8
Rolling Friction Rolling friction is the force that acts on
rolling objects. Rolling friction is about 100 to 1000 times less
than the force of static or sliding friction
Slide 9
Fluid Friction Fluid friction opposes the motion of an object
through a fluid. Fluid examples: air, water, quick sand, and cake
batter Air Resistance is the fluid friction action on an object
moving through the air.
Slide 10
Newtons Three Laws of Motion
Slide 11
Newtons First Law of Motion The state of motion of an object
does not change as long as the net force acting on the object is
zero. An object at rest remains at rest An object in motion remains
in motion Newtons first law is sometimes called the law of inertia
Inertia is the tendency of an object to resist a change in its
motion.
Slide 12
Newtons Second Law of Motion Newton also learned that the
acceleration of an object depends on its mass Mass is the measure
of the inertia of an object and depends on the amount of matter the
object contains. Newtons second law: the acceleration of an object
is equal to the net force acting on it divided by the objects mass
Example: doubling the mass of an objects cuts its acceleration in
half
Slide 13
Newtons Second Law of Motion The acceleration of an object is
always in the same direction as the net force. The unit of
acceleration is m/s 2 The units of acceleration N/kg and m/s 2 are
equivalent
Slide 14
Newtons Third Law of Motion According to Newtons third law of
motion, whenever one object exerts a force on a second object, the
second object exerts an equal and opposite force on the first
object. Called Action and Reaction Forces The force your bumper car
exerts on the other car is the action force The force the other car
exerts on your cars is the reaction force The two forces are equal
in size and opposite in direction.
Slide 15
Newtons Third Law of Motion Swimmer used arms to push against
the water and create an action force The water exerts an opposite
reaction force on the swimmer The reaction force acts on the
swimmer and pushes him forward through the water Not all action and
reaction forces produce motion.
Slide 16
Newtons Three Laws Summary First Law Motion wont occur (or
change) unless a force acts on object Second Law Acceleration = net
force/mass Third Law Action/reaction equal and opposite = 0 net
force If not equal and opposite a change in motion occurs
Slide 17
Which Law is it? 1.The law that states that the unbalanced
force acting on an object equals the objects mass times its
acceleration 2.The law that states that for every action force
there is an equal and opposite reaction force 3.The law that states
that every object maintains constant velocity unless acted on by an
unbalanced force 4.Describes action and reaction forces 5.States
that a comet wont stop moving until it hits something 6.States that
the more massive the object the more force needed to accelerate
it.
Slide 18
9/11/12 Ticket out the door Summarize Newtons Three Laws You
may use bullet or paragraph form Try and put them in your OWN
words