Download Forces 2014-15 v2 - McKinney ISD Staff Sites

Forces of Motion
Force
• A force is a push or pull exerted
on an object in order to change
the motion of an object
• Force has two things
– Strength
– Direction
Units
• Force is measured in something
called Newtons
– Named after Isaac Newton
– Are in units of kg (m/s^2)
• Kg = Mass
• m/s^2 = Acceleration
• Force = Mass x Acceleration
Net Force
• Net Force is simply the combination
of all the forces acting on an object
• Ex) Two guys try to move a piano.
One guy is pulling with a force of 30
Newtons and another guy is pushing
with a force of 24 Newtons. What is
the net force on the piano?
24 N
30 N
=
Net Force
• A guy is trying to push a desk
across a carpet floor. He is
pushing with a force of 35
Newtons and the carpet’s friction
is slowing it down with a force 9
Newtons. What is the net force?
9N
35 N
=
Balanced Forces
• Balanced Forces are when the
forces on an object produce a net
force of 0 Newtons.
• In other words the balanced forces
will not cause a change in the
motion of a moving object or make
a non-moving object start moving
Unbalanced Forces
• When the net force on an object is
not 0 Newtons, the forces on the
object are said to be unbalanced.
• Unbalanced forces cause a
change in the motion of an object
and are necessary to get an object
to start moving
Balanced and Unbalanced
Forces
• If two teams of people are playing
tug of war and each team is
pulling the rope with a force of 12
Newtons. Is the rope balanced?
What is the net force?
Balanced and Unbalanced
Forces
• What if there is an elevator of people
with a force of 195 Newtons pulling
down and a tension force of 317
Newtons pulling up. Is the Elevator
balanced? What is the net force?
Types of Forces
• There are several types of forces
of motion
– Some increase motion
– Some oppose motion
Friction
• Friction is a force that opposes
motion between two surfaces that
are in contact
• Examples include
– Rubbing hands together
– Pushing a heavy object over a rough
surface
– Pouring sand on ice
Gravity
• A force of attraction between
objects due to their masses
• We consider gravity a downward
force on Earth, since everything is
pulled toward its center
Buoyancy
• Buoyancy is the force that pushes
objects that are less dense than
water upward
• Example
– Ships
– Person in water
– Block of wood
– Inner tube
Tension
• Tension is the pulling force
applied to a rope or a spring that
attempts to stretch it out
Tension
• If you walk your pet, you would
use a leash or a rope. There
would be a tension force in the
rope if it was trying to walk faster
than you
• Ex) Your pet pig pulls you down
the street with a force of 12
Newtons
Magnetism
• A magnetic force is found between
two magnets
• The magnetic force can be
repulsive or attractive
– Attractive force = a positive end
and a negative end
– Repulsive force = two positive ends
or two negative ends
Magnetic Force
• Each magnet has a positive and
negative end.
• Opposites attract, Same repels
Normal Force
• Normal Force is the force of an
object pushing back against an
object pushing on it.
• Ex) Person on a chair
Book on a desk
Box on the ground
The End