Transcript Forces - Home | South McKeel Academy

Forces
Forces
A force is a push or pull that causes
changes in motion.
It can speed things up, slow things
down, or make things change
direction.
There are different kinds of forces:
friction, gravity, and magnetic force.
Nothing changes direction, speed, or
position without force.
Friction
A force that works against
motion.
It can make things slow
down or stop, or it can
keep things from moving
at all.
Whenever surfaces touch
you have friction.
Friction makes heat (rub
your hands together; there
is friction).
Can cause you not to slide
down a surface smoothly.
Gravity
The attraction
between you and the
Earth.
Pulls us to the Earth.
Causes things to
speed up as they fall.
Gravitational force
states that all objects
pull on each other.
Magnetic Force
An object that attracts
iron is a magnet.
Magnetic force is the
force that is exerted
by a magnet.
Magnets can attract,
repel, or push each
other away.
Compasses use
magnetic force to help
us navigate.
Balanced Forces
Balanced forces act on
an object but balance
each other out (think
about 2 teams playing
tug of war, when
neither team can pull
the other team down
you have a balanced
force).
Forces are balanced as
long as they are not
moving.
Unbalanced Force
When unbalanced
forces act on an
object, motion
changes.
The object may
start, change
direction, speed
up, or stop.
Example of Balanced and Unbalanced
forces working together
A seesaw shows
balanced and
unbalanced forces.
If the weight on one
end of the seesaw is
heavier than the
other, the heavier side
goes down (they are
unbalanced), if the
weight is the same the
forces are balanced
and the seesaw does
not move.
Net Force
The combination of all
forces acting on an
object.
When forces are
balanced the net force
is 0.
If 2 children are
pulling a toy and one
pulls the toy away
from the other then
the net force is
unbalanced.
Buoyant Force
Upward force.
Acts in the opposite
direction then weight.
Helps objects float.
If an object’s weight is
greater than the
buoyant force than
the object sinks.
Ships float because
they are not solid and
they are filled with air.
Work
Using force to
move an object
through a distance.
Work=Force X
Distance
You know that
work has been
done when
something moves a
distance
Machines and Work
Machines make work easier.
A simple machine is a tool that makes a task
easier by changing the strength or direction of a
force.
A lever is a bar that makes it easier to move
things. They have two parts; the lever arm
which moves and the fulcrum or the balance
point. The fulcrum supports the arm but doesn’t
move.
A wheel-and-axle helps you open a door.
A pulley is a wheel with a groove for a rope.
An inclined plane is a ramp. A wedge is made
up of 2 inclined planes.
Levers
Wheel-and-Axle
A doorknob is a
wheel-and-axle.
The knob is the wheel
and the rod that goes
through the door is
the axle.
Includes a wheel and
an axle.
A potter’s wheel uses
a wheel-and-axle.
Pulley
A flagpole uses a
pulley to raise and
lower the flag.
Inclined Plane
Ramps
Simple Machines
Building a house
involves using
simple machines.
Screws are inclined
planes.
Nails are wedges.
Hammers are
levers.
Compound Machines
Made up of two or
more simple
machines.
Make work easier.
Sailors and movers
use block and tackle
machines to move
heavy loads.
Examples are a push
lawn mower (wedge
and wheel-and-axle)
and hand operated
can opener (wedge
and wheel-and-axle).
Compound Machines
Shovels ( the blade
is a wedge and the
handle acts as a
lever).
Questions
What forces affect objects on Earth
every day?
What are balanced and unbalanced
forces?
What is work, and how is it
measured?
What is the purpose of a machine?
Name four types of simple machines.